THE BOOK OF WIRELESS TELEGRAPH & TELEPHONE A . FREDERICKCOLLINS CORNELL UNIVERSITY LIBRARY FROM Cornell University Library arV18679 The book of wireless telXWh,^^^^^^^ 3 1924 031 228 012 olin,anx < THE BOOK OF WIRELESS TELEGRAPH AND TELEPHONE By A. Frederick Collins The Book of Wirelesa Telegraph and Telephone The Book of Stars The Book of Magic The Book of Electricity Gas, Gasoline and Oil Engines The Amateur Chemist The Amateur Mechanic How to Fly The Home Handy Book Keeping Up With Your Motor Car Motor Car Starting and Lighting D. APPLETON AND COMPANY Publishers New York THE BOOK OF WIRELESS TELEGRAPH AND TELEPHONE BEING A CLEAR DESCRIPTION OF WIRELESS TELEGRAPH AND TELEPHONE SETS AND HOW TO MAKE AND OPERATE THEM. TOGETHER WITH A SIMPLE EXPLANA- TION OF HOW WIRELESS WORKS BY A. FREDERICK COLLINS INVBNTOK OP THE W1RBLESs"tBLEPH0NB AUTHOB OF "WIBBLBSa TELEGBAPRY. ITS HISTOBT, THEOBT AKD PBACTZCB, DESIGN AND CONBTRUCTION OF INDUCTION COILS," "book op blectricitt," etc. FULLY ILLUSTRATED D. APPLETON AND COMPANY NEW YORK : : 1922 : : LONDON COFIHIGHT. 1915. 1922, BT D. APPLETON AND COMPANY Printed in the United States of Amerioa TO OSCAR A. DE LONG, JR. a MAE£3l OF GOOD WIBELBSS XHINOe Cornell University Library The original of tliis book is in tlie Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924031228012 A WORD TO THE BOY Wireless is a thrilling pastime. Fancy a boy sitting in his room at home with his fingers on a telegraph key and a telephone receiver to his ear listening-in to the news of the world as it is flashed out from the great coast stations or hy ships far out at sea ! It's a great experience. Yet thousands of boys are doing this wonderful thing every day and night of the year, and you, my young friend, can do it as easily as they, for any boy can own a real wireless station, if he really wants to. If you have sharp eyes, you will see everywhere you go webs of vrire spim from the housetops and barngables, or spanning backyards, and often frontyards, too. These wires are not clothes lines ; no, indeed ! They have a far higher and, I should say, as useful a purpose as clothes lines, for they are wireless wires. These wires are called aerials by wireless operators. The word aerial may sound a little hard at first, and there are some other words used in wireless that are hard for the outsider, but they get to be very common words to the boy who puts up his own station, for there is no lesson so easily learned as the one taught by the thing itself, and no school like that of doing things yourself. Some of these aerials have a stretch of only twenty to thirty feet of vnre, while others have upwards of 1,000 feet, the amount depending on the place, the pocket-book and the boy. But you don't need to spend a lot of money to put up a good wireless station, for I have many boy friends who made all the apparatus they use, except the telephone receiver, and their sta- tions work as well as those of some others I know who bought their outfits ready for use. yiii A WORD TO THE BOY To be a wireless boy and make your own apparatus is to hare the kind of stuff in you of which successful men are made — men who, if they were shipwrecked on a desert isle at daybreak, would have something to eat by noon, a spring bed to sleep on by night and a wireless station the next day sending out SOS to ships below the horizon, for help. In nearly every city there is an electrical supply store where you can get all of the different parts named in this book. If you live in a place where there is no dealer, then write to the Man- hattan Electrical Supply Co., 17 Park Place, New York City; the J. H. Bunnell Co., 32 Park Place, New York City; and the Interna- tional Brass and Electric Co., 176 Beekman Street, New York City, and they will quote you prices. For continuous wave telegraph and telephone sending and re- ceiving apparatus write the Radio Corporation of America, Wool- worth Building, New York City. A. Fredeeick Collins, "The Antlers," Congers, New York. CONTENTS PART I A DEMONSTRATION WIRELESS OUTFIT CHAPTER FAGIi I. The Sender 1 II. The Eeceiver 12 III. A Cheap Aerial Wire 23 IV. Learning the Morse Code 34 V. How Wireless Works 42 PART II A LONG DISTANCE WIRELESS SET I. The Transmitter 54 II. The Receptor 81 III. A Good Aerial Wire System 112 IV. Tuning Transmitters and Receptors .... 136 PART III CONTINUOUS WAVE WIRELESS TELEGRAPHY AND TELEPHONY I. The New Wireless 155 II. Vacuum Tube Receiving Sets 158 III. How Vacuum Tube Receiving Sets Work . . 175 rv. Vacuum Tube Transmitting Sets .... 182 V. How Vacuum Tube Transmitters Work . . . 198 VI. Useful Information 201 Appendices 204 Definitions of Some Words and Terms Used in This Book 209 Index 219 LIST OF ILLUSTRATIONS MG. 1.- 2.- 3.- 4.- 5.- 6.- Y.- 10.- 11.- 12.- 13.- 14.- 15.- 16.- 17.- 18.- 19.- 20.- 21A 21B 22.- 23.- 24.- 25.- 26.- 27.- 28.- 29.- 30.- 31.- 32.- 33.- 34.- 35.- 36.- 37.- 38.- 39.- 40.- -A dry cell .... -Binding post used on dry cells -A battery of dry cells . - -The strap key complete . -Brass strap for key -Brass strap bent . -The base as it looks when finished -Binding post used on key and spark-coil -Wood screw binding post -The spark-coil complete -Interrupter of spark-coil -Spark-gap on the coil . -Spark-gap made of zinc rod . rllow sender is connected up . -Base or block for switch -Top of base showing where holes are drilled -Contact leTer showing size and where holes are drilled -Contact lever with handle -Cross section view of switch -Switch complete . — Cross section of a simple crystal detector — Base of detector -The simple crystal detector complete -Telephone receiver taken apart -Receiver complete .... -Telephone cord .... -The receiving set connected up -Aerial suspended between house and bam -Spreader with holes -Porcelain insulator -Spreaders with insulators and wires -Eope through spreader . -Aerial completed and put up -Base of aerial switch -Lever of aerial switch -Strip of brass of lever . -Cross section of aerial switch -Brass strip for contact spring. -Contact spring .... -Aerial switch complete . -The sender, receiver and aerial wired up and ready for business 32 lines si LIST OF ILLUSTRATIONS no. 41. — ^Xntemational Morse Code 42. — First aid to remembering the code 43. — ^Length of dash .... 44. — Space between, two letters 45. — Space between two words 46. — ^Abbreviation in code 47. — A current of water flowing in a coil of pipe 48. — ^A current of electricity flowing in a coil of wire 49. — A bar of iron magnetized by current of coil 60. — Currents are set up in tbe secondary by magnetic 51. — ^How a rubber ball bounces .... 62. — ^Electric current in an aerial wire 53. — ^Electric waves around aerial 64. — ^Electric waves thrown off by aerial 55. — Magnet and diaphragm of telephone receiver 56. — A strong current pulls diaphragm to magnet 57. — When current stops diaphragm springs back 68. — The human ear shovidng ear-drum and auditory nerve 69. — Symbols used in wireless telegraphy 60. — ^Diagram of condenser, spark-gap and tuning coil 61. — ^Diagram of alternating current circuit 62. — Support for key 63. — Side view of key . 64. — Top view of key 65. — ^Key complete . 66. — Cross section view of water 67. — Top view of water resistance 68. — Cross section of collar . 69. — Cross section view of Leyden 70. — Spring of Leyden jar . 71. — Leyden jar complete 72. — Top view of Leyden jar condenser 73. — ^Leyden jar condenser complete 74. — Top view of spark-gap . 75. — Side view of spark-gap . 76. — End view of spark-gap . 77. — ^Adjusting screw support 78. — Adjusting handle .... 79. — ^Brass spark electrode 80. — Spark-gap complete 81-82. — Top and side view of tuning coil 83. — Top view of spring clip 84. — Side view of spring clip . 85. — Tuning coil complete 86. — ^Plan view of instruments on table 87. — Wiring diagram of connections . 88. — Transmitter complete and ready, for sending resistance ]ar LIST OF ILLUSTRATIONS xiii no. FAQB 89. — Wood core of tuning coil 82 90.— Cheeks of coil 83 91. — End view of tuning coil 84 92. — 'Cross section of tuning coil 84 93. — Binding post with wood screw 85 94. — Slides for tuning coil 85 95. — Brass plate for contact spring 85 96. — Contact spring finished 85 97. — Contact spring on slider 86 98. — Top view of tuning coil 87 99. — Receiving tuning coil complete 87 100. — ^How the loose coupler is made 89 lOlA. — Side view of crystal detector 91 lOlB. — Top view of crystal detector 91 lOlC. — -Diagram of a receptor with a loose coupler tuning coil 91 102. — Brass holder of crystals 92 103.— Brass finger contact 92 104. — Phosphor-bronze contact spring (plate) . ... 92 105. — Phosphor-bronze contact spring (bent) .... 92 106.— Brass collar . 93 107. — Brass arm for adjusting screw 93 108. — Adjusting screw ^ ... 93 109. — Brass spring 94 110. — Brass support rod 94 111. — Adjusting nut ■ 94 112. — Crystal detector complete 95 113. — ^Tin foil laid up with mica 96 114. — ^Dia^am showing how mica and tin foil are laid up . . % 115. — Condenser with soldered ends 97 116. — Condenser complete 97 117. — How the variable condenser is made 98 118. — Head telephone receivers ....... 101 119. — Top view of water potentiometer .... 102 120A. — Side view of water potentiometer 103 120B. — End view of water potentiometer .... 103 121. — Brass arm for water potentiometer .... 103 122. — Upper copper electrode - . 104 123.— Adjusting disk 104 124. — Lower copper electrode 104 125. — Water potentiometer complete 105 126. — Plan view of receptor table (aerial wires) . . . 105 127. — Wiring diagram of reception with potentiometer . . 106 128. — Wiring diagram of receptor with potentiometer . . 107 129. — Receptor complete and ready for receiving . . . 109 130. — Mast on top of the house 112 131. — The spreader for the ends 115 132.— The middle spreader 115 133. — Leading-in spreader 115 134. — Withe with two eyes 116 K5. — Electrose ball insulator IIS xiv LIST OF ILLUSTRATIONS FIG. PAGE 136.— S hook 114 137. — S hook linking ball insulator with withe . . . 114 138. — ^Brass spreader stop 115 139.— Thimble 115 140.— Shackle bolt 115 141.— Tackle block 115 142. — Joining the steel wire 116 143. — ^Insulated support for aerial wires .... 117 144. — Brass stops on aerial wire 118 145. — ^Leading-in insulator 119 146. — ^Leading-in insulator through window .... 120 147-148. — Top and side views of lighting switch . . . 120 149. — Angle contact plate 121 150. — Top view of anchor gap 121 151. — ^Anchor gap complete 122 152. — Base and contact supports for aerial switch . . 123 153. — Contact lever for aerial switch 124 154. — Side view of aerial switch ...... 125 155. — Aerial switch complete 126 156— The metal ground 127 157. — ^Plan view of transmitter, receptor and aerial switch connected together 130 158. — Wiring diagram of transmitter, receptor and aerial switch 132 159. — A pair of tuned pendulums 135 160. — ^A pair of tuned Leyden jars 136 161. — Non-tuned open oscillation circuit .... 139 162. — Strongly damped oscillations 140 163. — Tuned closed oscillation circuit 140 164. — Feebly damped oscillations 141 165. — Coupled open and closed oscillation circuits for trans- mitting 142 166. — Coupled open and closed oscillation circuits for re- ceptor 143 167. — ^Intermittent direct current produced from electric os- cillations 145 168. — ^Siniple hot-wire ammeter — ^top view .... 147 169. — Simple hot-wire ammeter complete .... 148 170. — Cheap hot-wire ammeter ...... 148 171. — ^Diagram of wave meter and sending tuning coil . . 149 172. — ^Fixed and movable plates of variable condenser . . 150 173. — The condenser complete 150 174. — The wave meter complete 151 175. — Oscillations of a spark discharge 159 176. — Development of the three-electrode vacuum tube detector 159 177. — Connections for a simple vacuum receptor . . . 161 178. — ^Parts for a simple regenerative receptor .... 163 LIST OF ILLUSTRATIONS xv hq. page 179. — Regenerative receptor with variometer .... 165 180. — ^Wiring diagram of resistance coupled amplifier receptor with crystal detector 169 181. — ^Two-step amplifier receptor with vacuum tube detector . 171 182.— The Arkay loud speaker 172 183. — ^The Magnavox loud speaker 173 184. — ^Wiring (hagram for heterodyne long wave receptor . . 174 185. — ^The conversion of damped oscillations into pulsating di- rect currents 178 186. — A demonstration C. W. wireless telegraph sending set . 185 187. — A demonstration wireless telephone sending set . . 187 188. — ^Parts of a 5- to 50-watt C. W. wireless telegraph sending set 188 189. — Wiring diagram of a 5- to 50-watt wireless telegraph send- ing set 190 190. — ^Parts of a 5- to 50-watt wireless telephone sending set . 194 191. — Wiring diagram of a wireless telephone transmitter . .196 192. — How the oscillations are formed in the oscillator tube . 199 193. — ^Brown and Sharpe wire gauge 204 194.— Vertical aerial 206 195. — Horizontal 1 (inverted L) aerial 206 196.— Horizontal T aerial 207 197.— Fan aerial 207 198.— UmbreDa aerial 207 THE BOOK OF WIRELESS EGRAPH AND TELEPHONE PART I A DEMONSTRATION WIRELESS OUTFIT CHAPTER I THE SENDEE Befare trying to make a wireless telegraph outfit to send and receive messages over long distances, it is better for a beginner to put up a small set first and learn how to work it and how it works. The very first thing to do is to get all of the parts of the sender and the receiver; connect them together, and put up an aerial. The next step is to learn the wireless code, that is how to use a telegraph key to make the dots and dashes which repre^ eent the letters of the alphabet and then — ^practice awhile. When you can send and receive five or ten words a minute it is time to get a larger set and when you are ready for a larger set, a larger set will no doubt be ready for you. All of the parts of the sets described in this book may be bought of dealers in electrical supplies, or they may be made at home. For the beginner it is, perhaps, better to buy certain parts ready made, especially the spark-coil, as the results will be surer. If, on the other hand, you want to make the parts of either of the sets described, drawings will be foimd with the sizes marked on them and if you will but follow as "well as you caii the simple directions which I have given you cannot go wrong. So now get busy. 1 THE BOOK OF WIRELESS CARBON BINDING POST BINDING ZINC Every wireless station is made up of three distract parts : (1) A sender, also called a transmitter, (2) A rfeceiver, also called a receptor, and (3) An aerial wire, also called an antenna, and a ground. The sender wiU be described in this chapter. There are four separate pieces of apparatus which go to make up this sender, and which with a suitable aerial and ground, will send messages over a distance of a quarter to half a mile. These pieces of apparatus are: (1) A battery, for pro- ducing a current of electricity, (3) A telegraph key, for making and break- ing up the battery current into dots and dashes, (3) A spark-coil, also called an induc- tion coil, which changes the current from the battery into high pressure electricity, and (4) A spark-gap, in which sparks are set up by the high • pressure electricity. The Battery. — A battery for producing a current of elec- ■tricity is made up of five or sis dry cells connected together with pieces of copper wire. A single dry cell is shown in Fig. 1. It is made up of a stick •of carbon set in a tall cup formed of sheet zinc, the space in be- tween beiag filled with a paste which acts upon the carbon and zinc and produces an electric current. Fig. 1. — A Drt Cell. THE SENDER 3 Look again at Fig. 1 and you will see that secured to the upper end of the carbon is a binding post and that to the upper edge of the zinc cup is fastened another binding post. Binding posts are used to make it easy to connect the ends of wiTes to the carbon and to the zinc. Fig. 2 shows the kind of binding post that is used on dry cells and is drawn full size. Five or six dry cells when con- nected together wiU give enough current to work the spark-coil. These cells are connected with each other as shown in Fig. 3, that is the zinc of one cell is con- nected with the carbon of the next ceU by a piece of copper wire about 3 or 4 inches long. Any kind of copper wire will do for the connections but the kind known as bell wire, that is copper wire No. 18 Brown and Sharpe gauge covered with cotton thread and soaked in paraffin. WIRE GOES HER SCREW FASTENED QN,Z1NC OR CARBON Fia. 2. — ^BiNDDTQ Post Used ON Dby Celi^. Fig. 3. — ^A Battery oy Dby Cblivs. such as is used for connecting up electric bells, may be bought for 10 or 15 cents a half-pound — about 75 feet — and a half-pound will be enough to connect up both the sender and the receiver. The Tel^rraph Key. — This need not be a regular telegraph key, but instead it may be a simple strap-key as shown in Fig. 4. A strap-key can be easily made by cutting a piece of spring sheet brass, or even tin will do, 4 inches long and ^ inch wide, as shown in Fig. 5, and drilling a hole i inch in diameter through THE BOOK OF WIRELESS BINDING POSTS STRAP BUTTON Fig. 4. — ^The Strap Key Complete. each end; then bend it at one end as shown in Fig. 6. This piece of brass is called a strap and from this comes the name, strap-key. Fig. 5. — ^Brass Stkap poe Kbt. For a button, cut off the head of a clothes-pin and screw it to the long end of the strap with a roimd-headed screw. Maka a wood base 4J inches long by 2^ inches wide and J inch thick Fio. 6. — Beass Strap B^nt. and driU three holes, each i inch in diameter, through the ham as shown in Fig. 7. Screw the short end of the strap to the board at the place THE SENDER 6 marked X so that the screw holding the button and the strap together will be directly over the hole at the other end of the base and which is marked contact screw. Put a machine screw having a nut on one end through this hole so that the head of the HOLE FOR BINDING POST SCREW —.^HOLEFOR •^^BINDING 30REW Fig. 7. — The Base as It Looks When Finishbd. HOLE FOR CONTACT-® SCH" Borew is on the bottom and the end sticks through the top of the board about VV of an inch and then screw on the nut. Next screw on two blading posts to the back of the board and THUMB SCREW WIRE GOES lUI UUIIIB-POST HERE WASHER MACHINE iSCRBW '' Fig. 8. — Binding Post Used on Ket and Spabk-Coik Fig. 9. — ^Wood Sc3iew BiNDiNQ Post. the key is ready to be wired up. These binding posts are a little different from those used on dry cells (see Fig. 2) in that they have holes drilled through them so that the ends of the wire can be slipped into the holes and are held tight when screwed down, as shown in Fig. 8 and Fig. 9. 6 THE BOOK OF WIRELESS Take some bell wire and connect tbe strap of the key, by bending one end of a wire around the screw, which holds it to the board, to one of the binding posts; then loop the end of another piece of wire over the screw and under the nut in front and connect with the other binding post. The dotted lines in Fig. 4 show how the key is connected up. The Spark-Coil. — The spark-coil, or induction coU, as it is often called, which is used to change the battery current into a Fig. 10. — The Spabk-Coil Complete. current of high pressure to make jump sparks is shown in Fig. 10. The coil, it will be seen, is mounted on top of a polished wood base, and is covered with a thin sheet of hard rubber or bookbinder's cloth. On top of the base at one end of the coil is mounted an interruptor — a device which makes and breaks the battery current several hundred times a minute. A full-sized view of the interruptor is shown separately in Pig. 11. Also at the right-hand end of the top of the base are two large binding posts, one for connecting in the wire from the bat- tery and the other for connecting in the key. Now every spark-coil, or induction coil, is formed of a little roU of soft iron wires, caUed a core, and around this core is THE SENDER 7 yroimd two or three layers of rather thick, insulated copper wire, that is wire that is covered with cotton thread ; this coil of wire is called the primary coH and the ends of this coil are connected to the large binding posts on the base through the interruptor. RMAruae ADJUSTIN^G SCREW VIBftATING SPRING VIBRATING „^^ SPRING POST ADJUSTING , SCREW POST CONTACT POINT BASE Fig. 11. — Intbbbuptob of Spabk-Coil. Around the primary coil is wound another coil of very fine in- sulated copper wire called the secondary coil. A glance at Fig. 10 shows another pair of binding posts on top of the coU. The ends of the secondary coil, in which the high pressure currents are set up by the current from the battery, are connected with these binding posts. The spark-coil shown in Pig. 10 is about 8 inches long, 4 inches wide and 5 inches high. When the coil is connected with a battery and two wires are screwed into the upper binding posts and the ends of these wires are drawn half an inch apart a bright, crackling spark will jump across the gap thus formed, and this is called a spark-gap. The Spark-Gap. — The spark is a very important thing in 8 THE BOOK OF WIRELESS wireless telegraphy, in fact the distance over which messages can be sent depends very largely upon the length and the kind of spark a coil gives. A thin, red spark has very little sending power, but a jot, snappy spark will send over long distances if the aerial and ground wires are right. Fig. 12. — Spabk-Gap on the Coil. For sending wireless messages a spark-gap formed of a pair of brass balls, or any other metal such as copper or zinc, and having a diameter of f inch or larger, is needed. Pieces of stiff brass wire 4 inches long and which will slip through the holes of the binding posts as shown in Fig. 12, must be screwed in, U 4" i ^ ^< Fig. 13. — Spark-Gap Made op Zinc Rod. or soldered to the brass balls. The wires are bent up to ke©p the spark away from the coil. I do not know of any maker of spark-coils who supply coils with spark-gap balls fitted to them. If brass balls are hard to get, or cost too much, another way to make a spark-gap is to cut off two pieces of brass or zinc rod having a diameter of at least f inch, and have each piece | inch long. Round the edges THE SENDER 9 oflE with a file and screw in, or solder on, the brass wires as shown in Fig. 13. This ends aU the work to make the spark-coil complete, and all that remains to be done is to wire up the different parts and connect the spark-coil with the aerial and ground wire. Connecting up the Parts. — Before connecting up the sender, the parts should be placed on the table or bench which is to be used for operating. The key should be placed on the right-hand comer nearest the operator; the battery near the right-hand comer away from the operator and the spark-coil a little to the left of the key and between the key and the battery. Fig. 14. — ^How the Sender is Connected Up The purpose of this plan is to have the key in the handiest position for the operator, the battery out of the way and the spark-coil where the adjusting screw of the interruptor is within easy reach. One of the wires of the battery is connected with one of the binding posts on the base of the spark-coil, and the other wire of the battery is connected with one of the binding posts of the key, while the other binding post of the key and remaining bind- ing post of the spark-coil are connected together, aU of which is clearly shown in the outline drawing. Kg. 14. After the aerial wire is put up it is connected with one of 10 THE BOOK OF WIRELESS the spark-gap binding posts while the other spark-gap linding post must be connected with a sheet of zinc, or of copper, buried in the earth, or if a water- or a gas-pipe is at hand the ground wire can be soldered to it as explained in Chapter III under the heading of Aerial Wires and Grounds. Adjusting the Sender. — Two adjustments will have to be made before messages can be sent and both of these are on the spark-coil. First set the spark-gap balls a half inch apart and then turn the adjusting screlv of the interruptor, which is shown in Fig. 10 to the right until the contact point just touches the vibrat- ing spring of the interruptor. Now press down the button of the key and if the interruptor is in adjustment a stream of sparks will jump between the brass balls of the spark-gap. Turn the adjusting screw of the inter- ruptor a little at a time until the sparks are white and crack clear and sharp. This done set the spark-gap balls so that they are only -J inch apart. The sender is now in adjustment and ready for operation. AU through this chapter I have told you what to do but there is one thing I must caution you not to do, and that is not to hold down the strap of the sending key any longer than it takes to make a dot or a dash. If you do not heed this warning your battery of dry cells wiU soon run down and you will have to buy new ones or else close up shop. Cost of Sendee When Bought op Dealers 6 Dry cells at 20e $1.20 Nickel-plated strap-key 50 Bell wire 10 Spark-coil, J-inch spark 6.00 Brass balls, per pair, J-inch diameter 50 Attaching brass rods to brass balls 25 Total $8.55 THE SENDER 11! Cost of Materials to "Miw, Sendee 6 Dry cells at 20c $1.20 Starap-key, brass, 10c; screws, 5c; 2 binding posts, 10c 25 Bell wire, 50 to 75 feet 10 Spark-coil, J-incb spark Interruptor 1.00 Secondary wire No. 32, Brown & Sharpe gauge 1.50 Primary wire No. 16, Brown & Sharpe gauge 25 Iron wire for coil 10 Tin foil for condenser 20 Brass rod for spark-gap 10 Attaching brass rod to brass balls 25 ^Binding posts 25 Shellac varnish 10 Total $5.30 CHAPTEB II THE BECEIVER A wireless telegraph receiver is a very simple affair and, with the exception of the telephone receiver which you will have to buy, the whole thing can be easily made and at a very small cost. The receiver I shall describe in this chapter will receive messages over far longer distances than the sender you have just n^de will send. In fact, it is much easier to make a receiver which will receive messages over long distances than it is to make a sender which will send over equal distances. Usually, when you have made your receiver and connected it up with your aerial, you will find there is a high power station somewhere within your range. There are four parts to this receiver, and with an aerial wire that is high enough and long enough, messages may be received from stations of from ten to fifty miles away, the distance, of course, depending largely upon the adjustment of your detector, and the power of the station that is sending. The various pieces of apparatus are : (1) A dry cell, for providing a current of electricity, (3) A switch, for cutting off the current from the dry cell when the receiver is not in use, (3) A detector, for changing the feeble electric waves, which strike the aerial wire from the sending sta- tion, into stronger electric currents produced by the dry cell, and i(4) A telephone receiver which changes the strong elec- tric currents from the dry cell into sound waves 60 that the ear can hear them as dots and dashes. 12 FiQ. 15. — ^Basb ok Biock fob Swrrca. Fia 16. — ^Top OF Babe Seownfo Wbebe Holes Aeb Dbillbd. 13 14 THE BOOK OF WIRELESS You don't need to bother Just now about how the difEerent parts of the receiver work, the main thing is to get the apparatus set up and in working order. The Dry Cell. — The dry cell is exactly like the one shown in Fig. 1, on page 2 ; one dry cell will give all the current needed to work the detector and the telephone receiver. The Switch. — To make a switch, saw out a block of wood 3 inches long, 2 inches 2" — O Q Li -1X- FiQ. 17. — Contact Lever SHowrNO Size AND Where Holes Are Drilled. wide and i inch thick, as shown in Fig. 15; the next dravnng, Fig. 16, shows the top of the board, or base, as it is called. Now drill two holes -J inch in diam- eter through the board 1^ inches apart at the places marked with the circles. In making this base and others for different parts of your wireless apparatus the sharp edges of the wood should be emoothed off with sandpaper as this not only makes the blocks look better but prevents their edges from getting dented. A coat of shellac varnish wiU also give them a more finished ap- pearance. The next thing to do is to cut a strip of sheet brass f inch wide and 2 inches long. This strip is called a contact lever for the reason that it makes contact with another part of the switch. Near the ends of the contact lever and at the places where the circles are drawn in Fig. 17, drill two holes IJ inches apart; make a little wooden knob or handle about f inch in diameter and ^ inch long and screw one end of the contact lever to it FlQ. 18. — Contact Lever Handle. With THE RECEIVER 15 WASHERS. HANDLE ROUNDHEAD I WOOD SCREW NU-C^ WASHERS' l_. nil, FLAT HEAD IS MACHINE SCREW FiQ. 19.— Cross Section View op Switch. S IIT"^-^''^'^ '^^^^ ^ooi screw; this will leave the round head of the screw projecting from the bottom of the brass lever. The lever with the handle is shown in Fig. 18. FiQ. 20.— Switch Compmitb. 1 1 inch long, put on a couple of brass washers to raise the lever 16 THE BOOK OF WIRELESS from the base a little; push the screw through one of the holes in the board; put on another washer, and last of all screw on a nut to keep the lever from working loose, but the lever must move smoothly back and forth. Through the hole in the base under the handle of the lever put a flat-headed machine screw f inch long and screw a nut on imdemeath the base. Now when the lever is brought . to the middle of the base the round head of the screw which holds the lever and the handle together and the flat head of the screw on top of the base wiU. meet exactly and so make contact with each other. A sectional view of the switch is shown in Fig. 19. The switch when it is finished looks a little different from the one shown in Fig. 20, for this is a picture of a switch that was bought ready made ; but they work just alike. A Simple Crystal Detector. — This is called a crystal detector, because a piece of galena, or other crystal, is used for one of the detecting elements. It is shown at A and B in Fig. 21. Make a base of hard wood § inch thick, 2 inches wide, and 3 inches long. Near one end bore a | inch hole and near the other end drill a | inch hole and screw in a binding post. Around the screw loop a Fig. 21A. — Cross Section of a Simple Crystal Detbctob. Fiq. 21B. — Base op Dbthctob. wire which is to connect with the ground. Cut off a piece of brass rod I inch in diameter and 1 inch long and drill a hole in one end I inch in diameter and to a depth of | inch. Heat the end of the THE RECEIVER 17 rod in an alcohol or a gas flame, and run it full of melted solder.* Force a bit of silicon or any other sensitive crystal into the solder so that when the solder is cold the silicon will be firmly imbedded in it. Solder a wire to the rod so that it can be connected with the aerial and force the rod down into the hole in. the base. Sharpen one end of a piece of phosphor-bronze wire. No. 28 or 30 Brown and Sharpe gauge, about 3^ inches long and bend the wire as shown in the cut; slip the blunt end of the wire through the BINDING PHOSPHOR BRONZE WIRE SILICON OLDER TOGROUNI TO AERIAL Fig. 22. — The Simple: Cbtstal Detectob Couflete. hole in the binding post. Now adjust the wire until the pointed end presses on the crystal and you will have what is called a cat- whisker detector. A battery is not needed to operate this detector with, as the electric oscillations that are set up in the aerial by the incoming waves supply the current. When a crystal detector is properly adjusted it is quite sensitive. The pointed end of the wire that presses against the crystal must not be too sharp and it must make good contact with the crystal. Besides silicon a large num- ber of other minerals can be used as the sensitive element. Iron ■ Wood^s Metal ie better because it melte at a temi>erature of boiling water. 18 THE BOOK OF WIRELESS pyrites OT fool's gold, as this kind of crystal is commonly known, makes a good detector, and galena, whose chemical name is lead sulfide, is largely used at the present time. Now take a common steel sewing-needle, about No. 9, and weight it by fastening a lead bullet to the middle of it with a drop of sealing wax and lay it across the leads. (See Appen- dix P.) The Telephone Receiver. — ^While there is not very much to a telephone receiver, yet it is a piece of apparatus that is hard to make, and especially one good enough to use for wireless work. It requires a skilled workman and jBne machine tools to make one good enough for even this small set. I shall not, therefore, encourage you, whether you are a beginner or an ex- pert operator, to try to make your own telephone receiver, but it is well to know the names of the different parts which form it. How it works will be told in Chapter V. A telephone receiver is formed of five chief parts, and these are: (1) A thin, round piece of sheet iron called a &ish, or diaphragm, (3) A small electromagnet, made of a magnetized steel bar and wound with very fine silk-covered copper wire, (3) A metal case which holds the electromagnet in place, (4) A cover, having a small hole in it and which screws on to the case and holds the iron disk, or dia- phragm, in place, and (5) A telephone cord, that is a pair of very flexible in- sulated wires bound together. Each part of the telephone receiver, except the telephone cord, is shown separately in Fig. 23, and the receiver is shown put together in Fig. 24. The telephone cord is shown in Fig. 25. The magnet is screwed to the bottom of the case and the ends of the fine wires of the magnet are connected to two screws in the side of the case and to which the telephone cord is con- THE RECEIVER 19 nected. The scre\rs are insulated with little rings of hard rubber slipped over them and these keep them from touching the metal case. If the screws were not insulated in this way the elec- Diaphragm Case with magnets Magnet Cover Fig. 23. — Tblbphoni Reqbiveb Taken Apaet. tricity from the dry cell would flow from one screw to the other across the case instead of flowing through the coil of fine wire around the magnet. The edge of the disk of sheet iron just fits the outside edge of the case but does not touch the top of the magnet, a space Fia. 24. — Rbceiveb Complbte. Fig. 25. — Telephone Cobd. being left between them of about ^ inch. The cover when screwed on the case holds the iron disk firmly by its edge, but does not touch it anywhere else, and thie allows it to vil>rate freely. 20 THE BOOK OF WIRELESS The receiver shown in Fig. 24 is called a watch-case receiver, because it is about the size of a watch. A watch-case receiver nickel-plated and with a hard rubber screw cap weighs about 6 ounces and can be bought for 75 cents or $1.00. An ordinary telephone cord 3 feet long can be bought for about a quarter. It is shown in Fig. 25. Connecting Up the Parts. — ^When you have all of the parts of the receiving set at hand, get a nice smooth board, about 1 TO GROUND ECEPTOR BASE Fig. 26. — -The Receiving Set CoNNEcma) Up. inch thick, 5 inches wide, and 8 inches long, for the base. Then mount the switch on the left hand side of it, the crystal detector on the right hand side, and screw two binding posts in between them and well toward the back. This will leave plenty of room on the base between them so that the telephone receiver can be laid on it in case you should want to move it. The proper places for the various parts are clearly shown in the outline drawing in Fig. 26. THE RECEIVER 21 First connect the wire leading to the aerial with the brass cup of the detector that holds the crystal; then connect the binding post of the detector that holds the wire with one of the large bind- ing posts screwed into the base of the receiving set and insert in it one of the terminals of the telephone receiver; connect the other terminal of the latter with the other large binding post and from this post lead a wire to one of the contact points of the switch. Finally connect the other contact point of the switch with a wire that leads to the water pipe, gas pipe or other ground. Adjusting the Receiver. — ^The only adjustment of the re- ceiving set that you need to make is to move the free pointed end of the wire of the detector about on the crystal, while you are listening in, of course, until you find a sensitive spot and then you can adjust the pressure of the wire on it until the sounds are the loudest. This receptor will receive waves sent out by a spark gap sender only as it is not tuned for receiving words or music. Also for this reason it will respond to a wide range of wave lengths and is not, therefore, very selective, as it is called. It receives best, however, when the transmitter is sending out wave lengths that it normally receives. When the switch is closed and the telephone receiver is held to the ear a slight sound, something like bacon fr3Tng in a skillet, can be heard. If, now, the detector is connected to an aerud wire and a ground and some operator from a station l^at is not too far away is sending, you will be able to plainly hear the dots and dashes as he clicks them off with his key, and if you can read the International Morse Code you wiU have the pleasure of picking the messages right out of the air as they shoot by at the speed of Ught. While this is the simplest receiver that can be made it is far from being the best, as it cannot be tuned and is very wasteful of the received energy. You can make a much better receiving set by including a tuning coil and a condenser. This arrangement will not only permit you to tune in any amateur or broadcasting sta- tion but the signals will come in much clearer and stronger as the energy of the received waves is conserved. n THE BOOK OF WIRELESS Cost of Recbivbk When Paets Are Bought Svritch $ .30 Telephone receiver 75 to 1.00 Telephone cord 25 Detectori 1.70 Two binding posts 20 Total $3.20 Cost op Recbivee When Pabts Abe Made Switch $ .10 Telephone receiver 75 to 1.00 Telephone cord 25 Detector 35 Two binding posts 20 Total $1.90 1 Can be bought of the J. H. Bunnell Co., Park Place, New York City. CHAPTER III A CHEAP AEBIAIi WIRE Although the aerial wire is merely two or three wires strung between two high places it is an important part of wireless and it must be put up right. There are three things which go to make a good aerial and these are: (1) To have the wires as high as possible, (2) To have as long a stretch of wire as possible, and (3) To have the wires well insulated at the ends. The first thing to do is to choose two places as high and as far apart as you can find and one of which is near your operat- FiG. 27. — Aeeial Suspended Between House and Bakn. ing room, and still have a clear sweep between them, that is, there should be no trees or anything else in the way to interfere. One end of the aerial should be put up so that it will come close to the room where your wireless set is located. Suppose, for example, that your house and the bam are 100 feet apart. Then the aerial wires can rim between the gable ends of the house and the bam as shown in Fig. 37. If there is no bam on your place^ attach the end of the aerial to a chicken-coop or 23 24t THE BOOK OF WIRELESS even to a near-by fence. Whatever you do though, get the aerial as high above the ground as you can. There are five parts to an aerial and these are : (1) The wire, of which the aerial is made, (3) The spreaders, for keeping the w^ires apart, (3) The insulators, for keeping the wires from touching the spreaders, (4) The rope, for suspending the aerial, and (5) The leading-in wire, which connects the aerial wires with the sending and receiving apparatus. Kinds of Wire. — Any kind of wire will do for an aerial, !but aluminum or copper wire about | inch in diameter makes a very good one, that is if the aerial is a short one. Iron wire is much cheaper than copper wire, but it is not nearly as good for wireless work. If you want to use iron wire, try to get regular telegraph wire; this iron wire is galvanized, which means that it is plated with zinc. Galvanized iron wire is better for aerials than ordinary iron wire as it does not rust and conducts elec- tricity better. If neither copper wire nor galvanized iron wire can be had, use any kind of wire you can get and never mind the size as long as it is strong enough to hold together when strung up. Get as Q Q Fia. 28. — Spbeader With Holes. many feet of wire as you need for the distance between the places where you intend to suspend the aerial. When you have the wire, cut it in half and lay the two pieces side by side on the ground. The Spreaders. — These are merely sticks of wood to keep the wires apart when they are in the air and to prevent them from getting twisted. For an aerial 100 feet long a stick, or spreader, at each end will be enough. For longer spans than 100 feet a spreader should be placed in the middle of the aerial. For the spreaders get two sticks about 4 feet long, 1 inch A CHEAP AERIAL WIRE 25 thick and 3 inches wide, and bore a hole f inch in diameter and 3 inches from each end; also bore two more holes of the same size at each end but 6 inches nearer the middle of the stick than the outside holes. Fig. 28 shows the spreader and the places where the holes are to be bored. The Insulators. — Just as ordinary telegraph wires are looped around glass insulators to keep them from touching the Fig. 29. — Porcelain Insulator. telegraph poles, so the ends of the aerial wires are passed through porcelain insulators to keep them from touching the spreaders. These insulators are tubes made of porcelain and are about I inch in diameter and 4 inches long. One end of the insulator is bulged out so that it cannot slip through the holes in the spreader. Fig. 29 is a picture of one of these insulators. -HI ■n PORCELAIN INSULATOR NAIL D^ Fig. 30. — Spreaders With Insulators and Wires. Four porcelain insulators will be needed for the aerial — two at each end. Push an insulator in the outside hole of each spreader. Now lay a spreader at each end of the wires on the ground with the heads, or bulged part of the insulators away from each other as shown in Fig. 30. Then slip the ends of the wires through the insulators and twist the end of each wire 26 THE BOOK OF WIRELESS around a nail so that the wires cannot slip out after the aerial is hoisted into the air and drawn up tight. The Eope. — The next step is to fasten a rope to each spreader. Bach piece of rope should he ahout 15 feet long, more or less as may he needed; put an end of one piece of the rope through the holes in a spreader, loop it back and splice, or tie it to the other part of the rope so that it cannot work loose. Fasten ■€ TO BARN HC Fig. 31. — Rope THROuaH Spebadek. a piece of rope to the other spreader in the same way. Fig. 31 shows how it is done. The Leadis^-in Wire. — The wires which connect the ap- paratus with the aerial are formed of : (1) The hridle, or loop of wire whose ends connect with the wires of the aerial, and (2) The leading-in wire, or wire connecting with the bridle and which is brought ia the room through the window and connects with the aerial switch. The Bridle. — To make the bridle, take about 8 feet of wire and twist one end to one of the aerial wires and twist the other end around the other aerial wire. These wires should be soldered to the aerial wires in order to make good connections. This is the part of the aerial wire which is called the iridic. The Leading-in Wire. — To the middle of the loop, or hridle, so formed, twist and solder another piece of wire and be sure A CHEAP AERIAL WIRE 27 this is long enough to reach down and through the window and to your apparatus. This piece of wire is called the leading-in wire. It is shown in Fig. 32. AWIRE SOLDERED JOIN Fig. 32. — ^Aebial Completed and Put Up. The Leadin^-in Insulator. — The aerial wire must not touch trees, buildings or other objects, but of course it must be sup- ported in the air by something, so porcelain insulators are put in the spreaders to keep the wires from touching the wood. This is done to keep the electricity on the wires from running away and soaking into the wood. Now this same thing wUl happen when the leading-in wire is brought from the outside of the house into the operating room unless it is well insulated. An easy way to insulate the lead- ing-in wire is to bore a hole f inch in diameter through the window sash and push a porcelain insulator as shown in Fig. 29 through it. The end of the leading-in wire of the aerial is pulled through the insulator in the window sash and brought down to the aerial switch in the operating room to which it is connected. 88 THE BOOK OF WIRELESS The Aerial Switch. — The purpose of the aerial switch JB to connect the aerial wire first to the sender and then to the receiver, or the other way about, depending on whether you want to send or receive a message. One thing is certain, the sender and the receiver must npt be -\it^ O-Hhoue L o 1/ J o ZEL G-H*'HOLE c^' 'HOLE J&HOiS.. ^O h- -1"- A Fig. 34. — Lever op AeBI AL Switch. Fig. 33. — Base op Aerial Switch. Q -«"HOLE I i T _t.. Fig. 35.— Strip of BEtASS OF Lever. connected to the aerial wire at the same time for the reason that the spark from the spark-coil would hum out the detector when messages are being sent; nor should they be connected when re- ceiving a message, for much of the current set up in the aerial wire by the incoming waves wiU flow through the sender and bo weaken the message. A CHEAP AERIAL WIRE 29 To make an aerial switch, get a board about 10 inches long, 7 laches wide and 1 inch thick. Drill three -J-inch holes at the places marked with circles as shown in Fig. 33. Make a lever of a piece of wood 1 inch wide, J inch thick and 10 inches long ; drill a J-inch hole at the place marked with a circle, and round off the other end with a knife to make a handle as in Fig. 34. Cut a strip of sheet brass 7 inches long, J inch wide and h .STRIP OF BRASS (fcREW^^ Fia. 36. — Gsoss Section op Aerial Switch. inch thick and drill a hole in each end so that when the strip of brass is laid over the wooden lever the holes will come exactly together. This piece of brass is shown in Fig. 35. The next thing to do is to put a wood screw through a hole m the strip of brass and screw it in the wood lever nearest the handle so that the head of the screw sets in flush, that is, even ;« 1 FiQ. 37. — Brass Strip for Contact Spring. Fia. 38. — Contact Spmmo. with the surface of the strip of brass. The lever is attached to the board by putting a machine screw If inches long through the upper hole in the board (see Fig. 35) and the upper holes of the wood lever and the brass strip ; before putting on the lever a couple of brass washers should be slipped on the screw so that the Tmder part of the lever will be raised away from the board a little and can be moved freely from side to side. so THE BOOK OF WIRELESS A cross-sectional view, as if the switch was split right down the middle, is given in Fig. 36 and shows how the washers and screws should be placed through the lever and the board. One thing more, cut out two pieces of spring brass 2^ inches long and I inch wide, and drill a -J-ineh hole in one end as marked by the circle in Fig. 37; then bend the strips into the shape shown in Fig. 38 and screw one to the left-hand side of the board and the ATRIAL Switch CoMPLBra!. Other to the right-hand side of the board. Put the screws in from the back of the board and screw two nuts on each screw on top of the brass contact springs. A wire is connected to each of these contact springs and another wire is connected to the top screw of the lever. These connections are easily made as the wire is bent round the screw between the nuts and the latter are then screwed down tight. Fig. 39 shows the aerial switch complete. The Ground Connection.— There is one thing you must look after to put your station in working order and that is the ground. To ground an apparatus means to connect it with a sheet of metal that is buried in the ground, or some metal A CHEAP AERIAL WIRE 31 object such as a gas- or a water-pipe which leads to and runs into the ground. A fairly good ground can be made by soldering a heavy wire to a sheet of zinc 3 feet by 4 feet and burying the zinc in the ground deeply enough so that it will always be moist. The ground wire need not be insulated from the building but it can be brought into the house and led to the operating room ia any way that is easiest. Connecting np the Sender and Beceiver to the Aerial and Ground. — Connect the top wire of the aerial switch to the leading-in wire of the aerial. To the left-hand lower wire of the aerial switch connect the wire of the binding post of the detector marked io aerial as shown in Fig. 40, which is a com- plete wiring diagram of the whole station. Connect the right- hand lower wire of the aerial switch to the binding post of the spark-gap marked to atrial switch. Connect the wire of the binding post of the detector marked ground with the sheet of zinc buried in the ground; and finally connect the binding post of the spark-gap marked to ground to the same wire that the detector is connected with and which leads to the zinc plate in the ground. In other words, one sheet of zinc furnishes a ground for both the sender and the receiver. All of the con- nections are clearly shown in the outline drawing Fig. 40. A single pole, single throw switch must be connected in be- tween the top wire of the aerial switch and ground wire as shown in Fig. 40. This switch is to protect your apparatus from what is called static electricity, that is electricity which charges the air and the ground just before the coming of a storm. When sending and receiving this switch is open, but always close it when you are through working. A switch of this kind can be bought, or if you want to make one you will find the drawings. Figs. 147 and 148, and description needed on page 151. Before using your set read the Fire Underwriters' Rules given in Chapter III, Part III, page 199. To send a message throw the lever of the aerial switch to the right and work the Morse key. To receive a message throw the A CHEAP AERIAL WIRE 88 aerial switch to the left; close the receiver switch and hold the telephone receiver to yoxir ear. When you have finished throw the lever of the aerial switch to the right as for sending, and always leave it in that position except when you are listening-in, as this prevents static elec- tricity from charging the aerial wire. When you have com- pleted your set you can connect your receiver with the aerial and listen4n, but you must not connect your sender to the aerial and send until you have obtained a license from the Government as explained in Chapter III, Part III. Cost of Matekuls to Make a 100- foot Aerial^ 250 feet of No. 14 Brown & Sharpe gauge copper wire $1.50 Or 250 feet of galvanized telegraph wire 60 2 4-foot spreaders 20 5 porcelain insulators (4 for aerial and 1 for leading in) 50 30 feet of |-inch manilla rope 60 Total cost for aerial with copper wire $2.80 Total cost for aerial with telegraph wire 1.90 Aerial Svittch Board $ .20 Screws, washers and nuts .15 Strips of brass -. 10 Total 46 Gbouito 1 sheet of zinc 3x4 feet 50 Total cost of aerial, aerial switch and ground $3.30 or $4.20 ' These are only approximate priees. Very often enough wire, rope, vood and zine can be found in the cellar, attie or woodshed to make the aerial, emUh and ground. CHAPTER IV LEARNING THE MOESE CODE In the early days of North American history certain tribes of Indians had a crude way of sending signals without wires. .When the Indians went on the warpath and they wanted to signal to others of their tribe some distance away that they were ready to scalp the pale-faces, which was usually at night, one of the braves would place a burning arrow in his bow and shoot the flaming signal high into the air. The distant watchers who were in on the secret would know at once what was meant when they saw its light. It was a way to signal without wires but it was not wireless telegraphy as it is done to-day. We have to remember though that the Indians were savages while we are highly civilized, or thiak we are. The point I want to bring out, though, is that a burning arrow, the letters of the alphabet or the clicking of a telegraph instrument may mean whatever we have agreed beforehand that they shall mean. In other words they are merely codes, that is signs and signals which convey our ideas to others. The Code. — In real vnreless telegraphy, a code of dots and dashes is used by operators to send and receive messages. The word code in telegraphy means a set of electric impulses or sig- nals, arranged in advance and which can be sent from one sta- tion to another station by the use of proper apparatus. This code is formed of a number of dots and dashes, and each letter of the alphabet is represented by a dot, a dash, or by dots and dashes together. For example, suppose you are at one end of the table and I am at the other end and we each have a pencil. Now suppose I tap three times on the table with my pencil like this 9 # and that we have agreed before- . 34 ■«-eyco*io«oi^ooo>o ^K^a a.>^x>-N *'**^ /?:--:n\ /'';"-V\\ '/C-'.'-^nn ;!:;::•;;! i;;!!!!!!! II!!!:!:;) Fig. 53. — Electhic Waves AROtrNs Aeriaii. Fig. 54. — Eusctric Waves Thrown Off by AesiaIi. tricity they are shaped more like the half of an oiange, as shown in Pig. 54. How Wireless Waves Are Detected. — As you learned in building the wireless set, the detector of the receiver is con- nected with an aerial and ground wire when receiving just as the spark-gap is connected with the aerial and the ground when sending. The detector has been called a wireless eye, for it so THE BOOK OF WIRELESS detects or makes known that whieli our eyes are unable to see, and that is feeble electric currents. Going back again to the experiment of throwing stones into a pool of water, if you will put a cork on the still water near the edge of the pool, you will see the cork bob up and down every time a stone strikes the water, or rather as soon as the wave set up by the stone reaches the cork. The cork is then a land of crude detector. When the electric waves sent out by the aerial wire of a sending station strike the aerial wire of a receiving station, elec- tric currents are set up in the aerial of the receiving station and run up and down the aerial wire through the detector and the ground wire exactly like the electric currents set up in the send- ing aerial, as shown in Fig. 52. Where the water waves caused the cork to bob up and down, the electric waves set up electric currents in the aerial wire and these run through the crystal detector, but they can't flow back again; the result of this action is to change them into pidsating currents which can flow through the telephone receiver and this energizes the magnet of it which in turn attracts the diaphragm and the movement of it makes a sound. Just the instant the electric current stops running up and down the aerial wire and through the detector, the magnet of the tele- phone receiver is de-energized and there is no further action until another train of electric ciurents flows through the detector. How ElecMc Currents Are Changed into Sound Waves. — We have seen how a current of electricity flowing through a coil of wire which is wound on a soft iron core makes a mag- net of it. The magnet of a watch-case telephone receiver is very smallj as Fig. 55 shows, and is a thin flat piece of steel which is in itself a magnet; this magnet forms the core on which is wound a large number of turns of sUk-eovered copper wire which is almost as fine as a hair. When the pulsating current of the detector flows through HOW WIRELESS WORKS 51 the coils of the magnet of the telephone, the steel core is mag- netized and any change in the amount of current flowing through the coils will vary the strength of the magnet. When a high-frequency current is set up in the aerial wire by an incoming wireless wave this current is changed by the MAGNET MAGNET MAGNET E < a I a < Q FiQ.55. — Magnet AND Fig. 56. — ^A Strong Fig. 57. — ^Whbn CtWr- DiAPHKAGM OF Tele- Cdrkent Pou^ Dia- rent Stops Dia- phone Receiver. phragm to Magnet. phragm Springs Back. detector as we have seen, into pulsating current and when this takes place the current from the dry cell can flow through the de- tector and the coils of the magnet of the telephone receiver. When the oscillating currents stop flowing in the aerial wire, there are none to be rectified, that is, to be made into pulsating currents, by the crystal detector and so, of course, there is no current to affect the coils of the telephone magnet. This is the way that high frequency currents running up and down the aerial and ground wires and through the detector are changed into pulsating currents that can energize the coils of the telephone magnet, and this, naturally, changes the strength of the magnet. The soft iron disk or diaphragm of the telephone (see Fig. 65) is set over and very close to the end of the magnet. The edge of the diaphragm is held fast between. the case and the cap of the receiver, but the center of the diaphragm which is directly over the magnet is free to move, or vibrate. 62 THE BOOK OF WIRELESS EARDRUM Now since every change in the amount of current which flows through the coil of fine wire changes the strength of the mag- net which forms the core, the diaphragm, since it is of soft iron, is pulled in toward the end of the magnet, as in Fig. 56, and when released it springs back as in Fig. 57. As the diaphragm moves to and fro very rapidly, or vibrates, under the action of the changing strength of the magnet it gives out a sound like a honey bee on a flower. How the Message Is Heard.— We have just seen that the diaphragm of a telephone receiver vibrates and that this vibra- tion is the cause of the buzzing sound we hear. Now let's see just why a dia- phragm when it vibrates sets up what we call a sound, and let's see just how our ears hear the ait waves which we call sound. When the dia' phragm vibrates it causes the particles of air all around it to dance exactly in step with it and if the telephone receiver is held close to the ear the air which is set into motion cannot get away, but is held like a cushion between the diaphragm and the drum of the ear. The human ear (see Fig. 58) is very much like a telephone receiver in that it also has a thin diaphragm, which we call the drum, but instead of being worked by an electromagnet it vi- brates whenever the air outside the ear is set into motion; this being the case when the diaphragm of a telephone receiver sets the air into motion the drum of the ear vibrates exactly with it. Fig, 58. — The Human Ear, Showing Eak-Dhum AND A0DITOKY NeRVE. HOW WIRELESS WORKS 63 Connected with the ear-drum is an apparatus which ends in the auditory nerve and this nerve in turn leads to the braia. The ear-drum acts as a sender and the auditory nerve as a wire and when the ear-drum vibrates the brain is set a-tingling and this is what we call the sense of hearing. This then is what happens when you hear the sounds a tele- phone receiver makes as it buzzes out the dots and dashes. The telephone receiver, then, mjakes a buzzing sound as long as the needle and the leads of the detector remain cohered, which is only as long as the electric waves last which strike the aerial. It must be clear now that for whatever length of time the key at the sending station is pressed down the telephone receiver will buzz at the receiving end. This is how wireless works in about as few words as it can be told. PART II A LONG DISTANCE WIRELESS SET CHAPTER I THE TEANSMITTEB After you have put up and used the small wireless set, the making of a long distance set described in this chapter will not be a very hard thing to do and its operation will be a real pleasure. The transmitter is made so that waves of a given length can be sent out and the receptor is made so that different lengths of waves can be received. The Government will not permit you to use a wave length that is more than 200 meters long, that is, 656 feet, but with the receptor waves of almost any length can be received and you can listetiAn to almost any station that is sending. All of the parts of this set are made of materials that are easily gotten and they are put together in as simple a fashion as possible. There are two things, though, you should know something about before you try to make and use this larger set. The first is how to read diagrams and the second is the first principles of the electric current. How to Read Diagrams. — In wiring together the different parts which go to make up the sender, but which we will from now on call the transmitter, and the receiver which is better called the receptor, to keep it from being confused with the tele- phone receiver, the following symbols, which are called conveu' tional symbols, will be used. When an arrow is marked across 54 -•I- -'I'H'hvO^ (^ CELL BATTERY DYN^AMO ALTERNATOR (Direct Current) (Alternatine Current] TRANSFORMER TRANSFORMER SPARK QAP 1 S CARBON ADJUSTABLE DETECTOR B-ESISTANCE KEY AERIAL SWITCH CONDENSER T EY 6 ^ AERIAL SPARK QAP CRYSTAL DETECTOR ADJUSTABLE TUNING CQIU III CONDENSER AERIAL AERIAL GROUND D GROUND SWITCH WIRES CONNECTED WIRES CROSSED TOGETHER WITHOUT TOUCHING -~-0- AMMETER VOLTMETER HOTWIRE AMMETER /| I DOUBLE POLE ADJUSTABLE "^NIFE SWITCH CONDENSER ^^^^ Fig. 59. — Symbols Used m Wihelbbs Telegbapbt. 55 56 THE BOOK OF WIRELESS a symbol, it means that the apparatus represented is adjustable. As an illustration, suppose we want to show a condenser, a tuning coil and a sparh-gap connected together. It is not neces- sary to draw a com- I I plete picture but I I ' ^ merely draw the Q <^ SPARK GAP symbols represent- ing these parts as shown in Fig. 60. Things to Enow about a Current.- Pig. 60. — Diagram of Condbnbek, Spakk-Gap . ^ AND TtTNiNG CoiL. describing the small wireless set the words current and pressure were used a great deal. A point has now been reached, though, where something more definite must be known about an electric current if a good station is to be built. An electric current flowing ia a wire, like water flowing in a pipe, has both quantity and pressure. When we speak of a current we usually mean both the quantity of electricity and the pressure which moves the quantity along the wire. But strictly speaking, current means quantity. (1) A current or quantity of electricity is measured by a unit called the ampere just as water is measured by a unit called the gallon. (3) The pressure of electricity is measured by the volt just as the pressure of steam is measured by the pound. (3) The watt is the unit of work done, or the unit of work capable of being done by an electric current, just as horse-power is the unit of work done or capable of being done by steam or water flowing in a pipe. To find the number of watts a current of elec- tricity develops multiply the amperes (quantity) THE TRANSMITTER 57 by the volts (pressure). Seven hundred forty-sui watts are equal to one horse-power. (4) When electricity is forced through a wire the wire opposes the passage of the current; this is called the resistance of the wire and resistance is meas- ured in ohms. It is just the same with water forced through a pipe for the size of the pipe and the friction due to the water rubbing along the pipe offers a resistance to the flow of the water. A Long Distance Transmitter. — In up-to-date wireless stations transformers have taken the place of induction coils which were formerly used and alternating current is employed to operate the transformers wherever it can be had. Where only direct current is to be had the transformer can also be used, but an interrwptor, which will also be described, is required. So whether you have alternating or direct current, the transmitting apparatus is just the same — except for the interruptor. When I say that this is a long distance transmitter, I mean long as compared with the one previously described. The United States Government will not grant a license to any boy whose station is fitted with a larger transformer than one kilowatt.^ Unless you use a very large aerial, a \ kilowatt transformer will give you all the power you need and this is the size I have taken for this set. A J kilowatt transformer will give you a sending radius of from 25 to 100 miles. The different parts required for this transmitter are : (1) A source of current to operate the transformer, (2) A transformer for stepping up the low-pressure cur- rent of the lighting mains, which is about 110 volts, to a high-pressure alternating current of about 10,000 volts, (3) A resistance for regulating the amount of current supplied by the alternating current mains to the transformer, 'One kilowatt is equal to alaout 1% horse-power. 58 THE BOOK OF WIRELESS (4) A telegraph hey, for making and breaking up the alternating current which supplies the trans- former into the Morse code of dots and dashes, (5) A condenser of Ley den jars which is charged by the high-pressure currents set up by the transformer and which discharges through (6) A sparh-gap and so sets up sparks, and (7) A tuning coil through which the high-frequency cur- rents set up by the spark-gap surges into the aerial and ground. If a direct current is used then (8) An interrupter will be needed to make and break the current in the primary coil. The Source of Current. — To obtain an electric current sufficient to operate a transformer, the current should be taken from the mains of an electric light or power plant. A battery powerful enough to work a transformer would be very costly to buy and to keep up. For this reason it is assumed that you have electric current for lighting purposes in your oper- ating room. In Fig. 47, page 43, a picture is shown of a pipe and a valve which resemble a battery connected with a coil of wire and a telegraph key. In these cases the current of water or of elec- tricity always flows in the same direction. An alternating current is different from a direct current in that it changes its direction 130 times a second, more or less. In a piston pump every time the piston moves up the water will be forced through the coiled pipe in one direction, and every time the piston moves down the water will flow in the other direction, so that if the piston is moved up and down like a pump-handle when pumping water, the water in the pipe will move first in one direction and then in the other direction regu- larly. In other words the water in the pipe will alternate in direction. This is also true of an alternating current of electricity and a Dfiachine for producing alternating currents, called a generator. THE TRANSMITTER 59 ALTERNATING CURRENT GENERATOR is SO built that the current changes its direction 120 times a second, or makes 60 complete reversals, or cycles as it is called, a second. A diagram including a generator, a primary coil of a transformer and a key is shown in Fig. 61. The Transformer. — A transformer for using alternating current is even a simpler piece of ap- paratus than an in- duction coil, since it does not have an in- terrupter. A transformer comprises three parts, and these are (a) a core, (b) a primary coil, and (c) a secondary coil. The core is formed of pieces of thin sheet-iron. See Fig. 189, page 171. A primary coil of heavy insulated wire is slipped over the leg of the core, the ends of the coil leading to a pair of binding posts mounted on the cheeks of the coil so that a connection can be made with the regulating resistance and one of the wires of the lighting mains. The secondary coil of fine wire is slipped over the other leg of the core and the ends of the coil are connected with the battery of Leyden jars. See Fig. 88, page 76. The size of this transformer is about 6 inches high, 9f inches wide and llf inches long. It weighs about 25 pounds and is rated at ^ kilowatt, about -^^ of a horse-power. PRIMARY" Fig. 61. — Diagram op Alternating Cdeeent ClECtJIT. 60 THE BOOK OF WIRELESS A complete description of how to construct a i kilowatt transformer is given on page 171, Chapter I, Part III. The Key. — A key having large contacts is required for breaking the current that feeds the primary coil of the trans- former where upwards of 10 amperes are used. A good substantial key can be made by following the draw- ings shown in Figs. 63, 64 and 65. The base is a block of wood 3 inches vdde, 6 inches long and f inch thick. The supports which hold the lever up off the base are pieces of brass about ^ inch thick, | inch wide and 1 inch high. The lower end is bent over i inch while in the upper end of ea-\ O BRASS OR ZINC f ] SPARK ELECTRODES \ / '^ ADJUSTING SCREW DfSK HANDLE L STEM SET SCREW _ f 4BINDING O \_yPOST SET BRASS SCREW SUPPORT Fig. 74. — ^Top View op Spakk-Gap. THE TRANSMITTER 69 ment has been made to permit the set screw to draw the ends of the support together and so hold the adjusting screw tight, The other support is like the one just described except the BRASS SUPPORT BRASS OR ZINC SPARK ELECTRODES ADJUSTING SCREW Fia. 75. — Side View op Spakk-Gap. large hole near the top is f inches in diameter and is not threaded and the set screw reaches through the support to the HANDLE BRASS ( SUPPORT Fig. 76. — ^End View op Spark-Gap. hole only, as shown in Fig. 74. The two supports are now screwed to the base as shown in Figs. 75 and 76. To make the adjusting screw cut a piece of brass from a 70 THE BOOK OF WIRELESS rod J inch in diameter and 2J inches long, cut threads on this rod so that it will fit the threaded support. On one end of the adjusting screw, screw a disk of hard rubber or hard wood SET CREWit Fig. 77. — ^ADjxrsTiNa Sceew Support. f inch thick and 1 inch in diameter, as shown in Fig. 78. Now screw the adjusting screw in the support. For the stem cut a piece of brass 1^ inches long and thread it at one end; slip it KJ«^ Fig. 78.— Adjust- ing Handle. Fig. 79. — Brass Spabe Electeode. through the hole in the other support and screw up the set screw, as shown in Fig. 74. Make, now, two spark electrodes of brass rod 1 inch in diame- ter and i inch thick and drill and tap threads in these (see Fig, 79) and screw one to the end of the adjusting screw and the THE TRANSMITTER 71 other to the end of the stem, and the spark-gap is completed as shown in Fig. 80. The Tuning Coll.— This simple hut important device is the chief means hy which the transmitter is timed and waves of the greatest force are sent out. A tuning coil for sending is merely a large numher of turns of heavy wire wound in a spiral form or helix, as it is called. To make a tuning coil, cut out two disks of well-seasoned Fio. 80. — Spakk-Gap Complete. wood 1 inch thick and T'J inches in diameter. Screw on with round-headed wood screws to these disks 8 sticks of hard wood f inch square and 13^ inches long, as shown in Figs. 81 and 83 and so forming a sort of drum. Next get 33 feet of hrass wire \ inch in diameter and wind it on a form made of wood that is about 7 inches in diame- ter so that the turns of wire are close together. When the wire is taken off this form and placed over the drum it will be found to fit it snugly. Turn up one end of the wire and cut threads on the end so that a binding post can be screwed on to it. Thread the other end the same way. Pass the bent end through a hole in the top of the disk a& shown in Fig. 83, screw on the binding post and slip the other end through a hole in one of the lower strips and screw on another binding post. To hold the wire in place drive insulated staples over the turns of wire where they cross the strips. Finish the tuning coil by screwing on to the bottom three blocks of wood, or better. INSULATORa Figs. 81 and 82.-Top anTs^e View ^Titning Con, 72 THE TRANSMITTER 73 porcelain knobs, for legs, all of which is shown clearly in Figs. 83 and 85. To connect the coil with the other parts of the apparatus and with the aerial wire make three clips of brass as shown in Figs. 83 and 84. Cut six strips of spring brass f inch wide and 2 inches long as shown in Fig. 83 ; bend the end of each piece to fit the wire of the coil and place the straight ends of a pair of these pieces on opposite sides of a thin piece of wood, hard fiber or brass and drill a hole through them for a small machine screw; push this screw through the pieces and screw a small -3 ■lilllllllK )lll? Fig. 83. — Top View of Spring Clip. Fig. 84. — Side View op Sphing Clip. binding post on tight as shown in Fig. 84. The coil complete is shown in Fig. 85. Connecting^ up the Apparatus for Alternating Current. — Having all of the parts of the transmitter at hand, lay them out on your operating table somewhat after the plan shown in Fig. 86. It really doesn't matter just how the different parts are placed on the table, though the key should be conveniently near the right-hand lower comer and the water resistance close to it on the right-hand side so that the current can be varied easily. The transformer may set well back and the spark-gap can be screwed to the wall where its action can be easily seen and yet be well out of the way. This will be better than to have it screwed to the table in the position shown. The tuning coil should be set so that the clips can be changed from one turn of wire to another easUy. The condenser will seldom have to be touched. In bringing in the electric light leads see that they are properly put np in accordance with the Fire Underwriters' Rules 74 THE BOOK OF WIRELESS which will be found in full in Book III, Chapter III, page 199. .While all of the connections are shown in the plan viev Fia. 85. — ^TuNiNa Coil C!ompletb. Fig. 86, the wiring diagram, Fig. 87, gives a clearer idea of the connections. For wiring up the different parts, use No. 13 THE TRANSMITTER 75 or 14 insulated electric light wire, is shown in Fig. 88. condenserSb^noart The transmitter complete WATER RESISTANCE 1 TO AERIAL SWITCH POWER CIRCUIT 11 d powEK^use SWITCH FiQ. 86. — Plan View op Instruments on Table. Connectdng up the Appaxatus for Direct Current. — Where direct current only is to be had an electrolytic interruptor must O TO AERIALV^ "*sw?F3fi 110 VOLT DIRECT OR ALTERNATING CURRENT MAINS RESISTANCE Pig. 87. — ^Wmraa Diagram of Connbctionb. Fk. 88. — Tbansmittbb Complbtk and Ready for Sending. 76 THE TRANSMITTER 77 be used to operate the transformer. When an electrolytic inter- rupter is used the water resistance is not needed, as the amount of current can be varied by adjusting the interrupter. The interrupter is connected in the primary circuit exactly the same way as the water resistance so that no change in the wiring need be made. The construction of an electrolytic inter- rupter is given in Part III, Chapter II, page 191. Adjusting the Transmitter. — After the apparatus is set up and connected with the aerial and ground raise the upper plate of the water resistance to nearly the top of the water so that the resistance will be high and hence keep tee large a current from flowing through the primary of the transformer. Have about four of the six Leyden jars connected together and set the spark-gap electrodes so that the gap is about -J inch long. New close the switch in the main line circuit, close the key and watch the spark-gap. If no sparks passy open the switch and let the plate down in the water a little farther. Repeat this operation until a good spark takes place in the gap. When too much current flows in the primary of the trans- former the spark will be red and stringy, and when this is the case use either less current or connect in more Leyden jars. The larger the number of Leyden jars the greater the amoimt of cur- rent which flows in the primary ceil. When the current and the Leyden jars have been adjusted so that a good, white, snappy spark results, the switch is again opened and the spark-gap elec- trodes are separated until the gap is about J inch wide. Kow change the position of the clips on the tuning coil, that is those clips which connect with the spark-gap and condenser imtil the longest sparks possible take place in the gap when the apparatus is roughly tuned. A much better and easier way to adjust and tune the ap- paratus is to use a hot-wire ammeter and this piece of apparatus is described in Chapter IV, Part II, page 146. ,78 THE BOOK OF WIRELESS Cost op Teansmitter When Bought of Dealers ' 1 i kw. transformer $20.00 1 regulating resistance 6.00 1 telegrapli key 4.50 1 switch (double pole) 50 1 tuning coil 10.00 1 condenser of 6-one-gallon or 12 half -gallon jars. . 15.00 1 spark-gap 5.00 1 fuse block 25 1 roll of electric light wire 50 1 dozen porcelain insulators 25 Total $62.00 Cost of Transmttteb When Home Made i Jew. transformer^ 17 pounds sheet iron @ 6c $ 1.02 3 pounds No. 13 double cotton-oovered magnet wire @ 35c 1.05 5 pounds No. 34 double cotton-covered magnet wire @ $1.10 5.50 10 yards empire cloth 5.00 Base for coil 25 2 binding posts 20 Total $13.02 Water Resistance 1 1-gallon jar or crock $ .10 2 dishes of zinc or brass 25 1 brass eoUar with set screw 50 2 binding posts 20 1 brass rod 25 Total $1.30 "The prices of the various parts of the apparatus as given below are only approximate and it is well to get prices from a number of dealers before buying. 'A full description with drawings for making a % kilowatt trans- former is given in Chapter I, Part III, page 153-. THE TRANSMITTER 79 Telegraph Key Wood base $ .10 Brass bar 20 Adjusting screw 10 2 supports 30 Button 10 2 silver contacts 25 Screws 05 2 binding posts 20 Switch double pole 50 Fuse block 25 Total $2.05 Leyden Jar Condenser 6 1-gaUon glass jars $ .50 1 poTind tin foil 60 6 turned wood covers 30 7 binding posts 70 1 pint of shellac varnish 10 Sheet brass for springs 25 Wood box 1.00 Total $3.45 Tuning CoU 2 wood dishes (top and bottom) $ .20 8 wood strips 13J inches long 25 32 feet of :i-inch brass wire 1.50 Brass wood screws 10 Insulated staples 20 3 porcelain insidators 06 4 binding posts 40 Spring brass for clips 15 Flexible lamp cord for clips 50 Total $3.36 80 THE BOOK OF WIRELESS S park-Gap 1 slate base $ .25 2 brass supports cut and threaded •. . . .50 1 adjusting screw threaded 25 1 stem (threaded) 15 1 hard rubber handle 25 2 iron electrodes drilled and tapped 50 2 binding posts 20 Total $2.10 Koll of electric light wire 50 1 dozen porcelain insulators 30 Total cost of transmitter $26.02 CHAPTEE II THE EECEPTOE A good wireless receptor which will give you a lot of pleasure and service can he easily made — except the head telephone re- ceiver — ^by following the drawings and descriptions given in this chapter. While this receptor is not the best that can be made, still messages up to 500 miles or so can be received with it, the dis- tance, of course, depending upon the length and height of your aerial, the power of the sending station and the adjustment of the apparatus. There are a large number of wireless boys who have only a receiving apparatus connected with their aerials, and although they cannot send messages they can receive them from any station within their range. The Government has a great wireless station at Arlington, Virginia, which has a sending range of over 3,000 miles and there are other Government stations scattered all over the United States, all of which send out the standard time daily and if you live within signaling range of one of these stations you can re- ceive the correct time every day without cost. A Government license is not required where only a receiving set is used. The various parts needed for a receiving set are : (1) A tuning coil, for tuning the aerial wire so that waves of only a given length can be received. Thus any station can be tuned in or out as desired. (2) A crystal detector, for changing the high-frequency cur- rents which surge in the aerial wire and tuning coil into a direct current, capable of operating the telephone receiver. 81 82 THE BOOK OF WIRELESS (3) A STnall condenser, which with the tuning coil and the detector forms a closed circuit. (4) A telephme receiver, for changing the direct current passing through the detector into sound waves so that the ear hears them as dots and dashes. (5) An adjustable resistance, called a potentiometer, for Fig. 89. — Wood Cobe op Tuning Coil. regulating the amount of current flowing through the detector from a dry cell. (6) A dry cell for producing the current which flows through the detector, and (7) A small sviitch, for opening and closing the dry cell cir- cuit. The Tuning Coil. — ^For this receptor you can use either (1) a close-coupled tuner, or (2) a hose-coupled tuner. The first kind is the easiest to make and you can tune in or out the waves of send- ing stations, but the second kind tunes the sharpest and gives the best results generally. A Close-Coupled Tuning Coil. — This tuner is made with three sUding contacts and consists of a frame which holds: (1) A core made of a cylinder of wood or a piece of glass tubing on which is wound (2) a single layer of insulated wire, the insulation being scraped off on three sides of the coil so that (3) the brass sliders whose springs make contact with the turns of wire can be moved freely back and forth over them. To make the tuning coU get a wood worker to turn for you a cylinder of well-seasoned hard wood 8| inches long and 2f inches in diameter and boil it in paraffin. In this cylinder § inch from each end put a small wood screw as shown in Fig 89, when it is ready for the wire. The THE RECEPTOR 83 best kmd of wire for this purpose is known as enameled wire, but if you cannot get this easily use double cotton-covered mag- net wire. A I pound of No. 32 wire. Brown and Sharpe gauge, will be enough of either kind. Before you begin to wind the wire on the cylinder, twist an -¥i — X- Fig. 90. — Cheeks op CoiIi. end of the wire around one of the screws and put the screw in tight with a screw-driver as this end is not to be connected with anything. As you wind on each turn of wire, draw it tight and press it up close to the last turn. When you have wound on enough wire so that the turns reach the screw at the other end, twist the wire around the screw and drive it down tight, but do not cut lie wire off short, for this end is to be connected with a binding post. If cotton-covered wire is used it should be well shellacked i. Fig. 91. — Eira View op Tuning Coil. Fig. 92. — Cross Section of Tuning Coil. 84 THE RECEPTOR 85 and allowed to dry before assembling. But whether the wire is enameled or cotton-covered the insulation must be scraped off on a line | inch wide and the whole length of the coil on the three sides where the springs of the sUders are to make contact with the wire. With enameled wire this is an easy thing to do and a neat job will result, but with cotton-covered wire it is not so easy and a poor-looking job is likely to come of it. For this reason it is better to use enameled wire if it can be had. The cheeks of the coil, as the wooden ends are called, are next in order. These should also be made of well-seasoned hard wood and should be 4| inches square and f inch thick. Fia. 93. — BiNDiNa Post With Wo<» SCBEW. Now on each of the three sides draw a line f inch from the edge as shown in Fig. HH' HOLE , TAPPEDFQR SCREW 9ii' HOLE FOR BRASS ROD I Fig. 94. — Sudes for Ttjning Coil. Fig. 95. — Brass Plate fob Con- tact Spring. 90 by the dotted lines. Measure from the middle of these lines i inch each way, and make a point with a pencil and drill a hole ■h inch in diameter. This will make six /q "~~^ holes, two on each side and the holes on each W f side will be i inch apart, from center to cen- '' tar, all of which is clearly shown in Figs, 91 and 92. Smooth the cheeks up with sandpaper and give them a coat of shellac varnish, and when dry screw them to the ends of the wooden coil with a wood screw and see Fig. 96. — Contact Spring Finished. 86 THE BOOK OF WIRELESS '/- y FiQ. 97. — Contact Spbinq on Suseb. that the coil is exactly in the centers of the cheeks as shown in Figs. 91 and 92. On the edge of the cheek nearest the free end of the wire on the core put in a binding post having a wood screw on its base, as shown in Fig. 93. Having made all of the easy parts of the coil you wiE now come to something a little harder — in metal. Get six pieces of round brass rods each of which is lOf inches long, and i inch in diameter; cut threads on the ends of these rods about f inch down and get 24 washers large enough to slip over the rods, and 12 brass nuts to fit the threads cut on the rods. The next and last thing to do is to make the sliding contacts. These sliders, as they are called, are made of brass. Get three pieces of brass J inch square and 1 inch long, as shown in Fig. 94, and drill two holes in each one A inch in diameter and so that the centers of the holes are exactly ^ inch apart. These holes wiU have to be drilled very true or the sliders, when they, are put on the rods, will not run smoothly. Drill and tap a A inch hole in each slider between the larger holes but on a side at right angles to them as shown in Fig. 94. Spring brass will do for the springs which make contact with the wire of the core but springs made of phosphor-bronze are bet- ter. Make three springs of sheet brass or phosphor-bronze H inches long, -J inch wide at one end and ^ inch wide at the other end, as shown in Fig. 95; screw each spring to a slider and bend it over as shovm in Fig. 96. Drill a A inch hole through the wide end of the spring and screw it to the brass slider block as shown in Fig. 97. The next step is to put the tuning coil together. Slip a pair of the brass rods through the holes in each of the sliders and push the ends of the rods through the cheeks of the coil, when the contact springs should rest on the turns of wire where the insulation has been scraped ofE. Next slip a pair of washers over the ends of each rod and screw on the nuts. Fig, 98. — Top View op TimiNa Coil, FiQ. 99. — Receiving Toning Con. Completb. 87 88 THE BOOK OF WIRELESS Before tightening up the nuts cut off three pieces of heavy insulated wire about 4 inches long and after scraping the ends bright loop them around the rods between the washers as shown in Figs. 91 and 99. These wires are to connect the sliders with the ground, the condenser, and the detector as shown in the plan and the wiring diagrams, Figs. 127 and 128. Fig. 98 shows a top view of the completed tuning coil, the cheeks being drawn in cross section to show the rod a little better. The tuning coil complete is pictured in Fig. 99. The Loose-Coupled T imin g Coil. — For this tuner you will need: (1) a board for the base about 5 inches wide and 13| inches long; (2) two wood cheeks 4 inches on the sides for the primary coil; (3) two brass rods J inch in diameter, and 6| inches long and threaded on both ends; (4) a pasteboard or fiber tube 5f inches long and whose wall is not more than f inch thick; (5) two cir- cular wood cheeks 2| inches in diameter for the secondary coil; (6) a pasteboard or fiber tube having an outside diameter of 2| inches and a length of 5 inches; (7) two brass rods J inch in diam- eter and 13| inches long, threaded on both ends, for the second- ary coil to slide on; (8) one 7-point adjustable switch; (9) about i pound of No. 20 Brown and Sharpe gauge enameled copper wire for the primary coil; and (10) about the same amoimt of No. 26 Brown and Sharpe enameled copper wire for the secondary coil. To assemble the tuner, begin by giving the large tube a couple of coats of shellack varnish, then wind on one layer of the No. 20 wire, and scrape ofif the insulation f inch wide and the length of the coil; this is so that the slider can make contact with the suc- cessive layers of wire. One of the cheeks must have a hole sawed in it the diameter of the outside of the tube as shown at A in Fig. 100. Now smear glue on one end of the tube and set it in the hole in the cheek; lien thread one end of the wire through the small hole, marked x, in the other cheek, smear some glue on the other end of the tube and set it on the cheek and let it dry. Nejrt make a slider with a spring contact as I described for the close-coupled tuner; slip it over the guide rods and push the C-CHEEKS OF THE SECONDARVCOIL J A- CHEEKS OF THE PRIMARY COIL F-SUPPORT BLOCK FOR THE SECONOARV COIL '^W^ 0-7POINT CONTACT SWITCH 1. .0* kS' END OF PRIMARY PRIMARV COIL B-CROSS SECTION OF THE LOOSE COUPLER 2. / 'TODETECTOR 1 tomeaoPHOnC E-WIRING DIAGRA.M.OFA LOOSE COUPLER e-THE LOOSE COUPLER COMPLETE 3. 4. Fig. 100. — How THE Loose CoueI^r is Made. 1. Parts of the Loose Coupler. 2. Cross Section of the Loose Coupler^ 3. Diagram of Wiring of Loose Coupler. 4. The Complete Loose Coupler. 90 THE BOOK OF WIRELESS ends of these through the holes in the cheeks at the top as shown at A and B. Screw a binding post on one end of one of the guide rods and screw nuts on the other ends of them. This done set the primary coil on the base so that the end with the binding post in it will come to within ^ an inch of the end of the base. Then screw them together, and the coil will be rigidly secured to the board. The primary coil completed, shellack the other paper or fiber tube and wind it with one layer of the No. 26 wire. Bring the ends of the wire inside the tube and count off the turns into five equal parts; scrape each of the equidistant turns, solder a wire to each one and bring it through to the inside of the tube as shown at B. Thread the seven ends of the wires through the little holes in the circular cheek (see C), and fasten each one to one of the contact points of the switch (see D), all of which is clearly shown in the wiring diagram at E. Now screw the switch to the cheek and then glue both cheeks in the ends of the tube. Finally screw the support block, F, on to, and 2 an inch from, the end of the base-board and slip the rods that are to support the secondary coil through the holes in the support block, thence through the holes in the cheeks of the secondary coil and on through the holes in the last cheek of the primary coil. Screw a nut on each end of the support rods and your loose tuner, which will look like G, is ready for service. The Crystal Detector. — ^This detector is a good one in that it is simple in design, there is nothing to get out of order, its adjustment is fine enough for all ordinary working and it is al- most as sensitive without using a dry cell as it is with one. While it is not absolutely necessary, it is a good plan to enclose the detector in a box or case, except the adjusting knob. This wUl protect the crystal from the action of the air and moisture. You can easily do this by making a box of thin wood and fitting a glass top on it so that you can see the crystal. The base of the detector may be made of a good piece of seasoned wood but slate of marble is better as these last materials are better insulators. Whatever material you use get a piece 3 AOJUSTINa SCREW PHOSPHOR SRONZe CONTACT 8PI BRASS WEU. FOR CRYSTAL POST FORMES 3 COLLARS Fig. lOlA. — Side View of Crystal Detector. BRASS WELL FORORYSTAI. ADJUSTING SCREW WELL SCREW WffiS CONNECTING WELL WITH BINDINQ POST Fig. lOlB. — Top View op Cktstal Detbctob. Fig. lOlC. — Diagram op a Re- ceptor WITH A Loose Codp- LBB Tuning Coil. HEADPHONES 91 92 THE BOOK OF WIRELESS inches wide, 5 inches long, and ^ or | inch thick. Drill three 5w inch holes in the base, two for the screws of the binding posts and one for the support ; now at ex- actly 3f inches from the center of the hole for the support drill a A inch hole for the well screw as shown in Fig,. 101. On the under side of the base ream out these holes until they are I inch in diameter and deep enough so that when the detector is put to- gether the ends of the screws will not come below the bottom of the base. The top of the base should be perfectly smooth. Fia. 102. — Brass Holder op CBTSTAIiS. Fig. 103. — Brass Fingeb Contact. Fig. 104. — Phosphor-Bronze Contact Spring (plate). The purpose of the well is to hold any kind of a crystal tightly so that a good contact Will be made. We will talk about the crystal presently. For the well cut a piece -J inch long from a brass rod 1 inch in diameter and drill a hole J inch in diame- ter through it; also drill a A inch hole parallel with the large hole through the rim so that the well can be screwed to the base as shown in Pig. 101; now drill and tap a hole through the ring and put in a ma- chine screw as shown in Fig. 102. Next take a strip of brass IJ inches long, f inch wide and i inch thick and saw out a slot in one end f inch long and A inch wide and drill a ^ inch hole through the other end as ahown iu Fig. 103. This piece is called a contact finger. A piece of sheet phosphor-bronze 1:^ inches long and f inch wide Fig. 106. — ^Phosphor-Bronze Contact Spring (bent). THE RECEPTOR 9S Fig. 106. — Brass Collak. Fig. 107. — Brass Arm tor Adjusting Screw. with one end cut to a point and a hole drilled in the other end, as in Fig. 104, is secured to the end of the iinger with a screw. This permits the point which makes contact with the crystal to be taken ofE if needs be. The point is then bent as in Fig. 105. The next step is to make four collars of round brass rod ^ inch in diameter, f inch long and drill holes through them A inch in diameter as shown in Fig. 106. Three of these collars are used to form the support which holds the springs and adjusting screw arm in position and the fourth collar is used to separate the free ends of the springs as shown in Fig. 100. The arm which holds the ad- justing screw is made of a piece of brass If inches long, -J inch wide and J inch thick; drill a hole in each end, make one of them A inch in diameter and thread it and make the other -h inch in diameter and leave this one smooth. The arm is shown in Fig. 107. The adjusting screw. Fig. 108, which fits into the threaded hole of the arm, is simply a machine screw IJ inches long with its end filed down to a point and having a disk of hard rub- i ber, or of wood, 1 inch in diameter and A inch thick forced on up to the head of the screw; a nut on the under side will keep it from slipping. Make two stiff springs of spring brass 2^ inches long, | an inch wide and about A inch thick (see Fig. 109). A A inch brass rod 2^ inches long, and a ^ inch brass rod 1^ inches long and both of which have their ends threaded (Fig. 110), to- gether with the adjusting nut (Fig. Ill) and a pair of binding posts, complete the parts of the detector. Fig. W— 108. — Adjusting Screw. 94 THE BOOK OF WIRELESS --aH" r Now take the two large springs and place one of the brass coUars between them at one end, slip the short threaded brass rod through them and screw on a nut. Slip the finger with the slot in it on the other end of the rod and screw on the adjusting nut. Put a collar between the springs at the other end and slip the longer threaded brass rod through the holes. Outside of each of the springs and over the rod slip a collar and on the collar next to the spring which carries the finger with the pointed contact set the adjusting screw Jiii Fia 109. — Brass Speing. T x ll Fig 110. — Brass Sup- port Rod. arm, put on a washer and screw on a nut. Push the end of the rod through the hole in the base, put a couple of washers on the end of the rod on the bottom side of base and screw on a nut, all of which is clearly shown in the side view of the detector (Fig. 101). Screw the binding posts to the base in their proper places and connect one of the binding posts with the brass well by means of a piece of insulated wire and the other binding post with the sup- port as shown by the dotted lines in Fig. 101, and the frame of your detector is done. It is shown in its completed form in Pig. 112. You will see that this detector has three means for adjustment, and these are: (1) The well can be moved from side to side; (2) the contact point can be moved forward and backward and from side to side, and (3) these two movements permit the phosphor-bronze point to be placed in any position on the surface of the crystal in the well, while the adjusting screw gives the needed pressure tae bringing the phosphor-bronze point i:ato contact with the crystal. Fig. 111. — ^Adjust- ing Ndt. THE RECEPTOR 95 There are many kinds of crystals used in crystal detectors, but the kind known as fool's gold, or to call it by its right name, iron sulphid, works about as well as any, but silicon is largely used. But all kinds of iron sulphid will not work as a de- tector, so when you order be sure to say you want the bright crystalline kind. The Condenser. — ^For this receiving set you can use either (1) a fixed condenser, or (2) a variable condenser. The former is Fia. 112. — Cbtbtal Dbtbctor Complete. very easily made but you will have to do all of your tuning with the tuning coil. The latter is troublesome to make and will probably cost you as much as a ready-made one. The advantage of a variable condenser is that you can tune very sharp with it. The Fixed Condenser. — To make tnis condenser get enough tin foil to make five leaves 1§ by 3 inches on the sides; and lay these alternately with the sheets of mica; that is, lay a sheet of mica down first; then lay a sheet of tin foil on top of the mica as shown in Fig. 113, with the end of the tin foil lapping over the edge of the mica J inch and on the right-hand side. This leaves a margin of mica J inch all around on the other three sides. Another sheet of mica is now laid on the tin foil, and an- other sheet of tin foil is laid on the mica, this time with' the 96 THE BOOK OF WIRELESS overlapping end on the left-hand side as shown in Fig. 114t and so on until all the sheets of mica have been used. The diagram {Fig. 114) shows the sheets of mica and leaves of Fig. 113.— Tin Foil Laid Up With Mica. tin foil separated but, of course, when the condenser is actually laid up the sheets and leaves are close together. LEFT Ristrr Fig. 114. — Diagram Showing How Mica and Tin Fon. Abb Laid Up. After the condenser is laid up, cut two pieces of stiff paste- board the size of the mica, place one on each side of the con- THE RECEPTOR 97 denser like the cover of a book, and put a rubber band round each end to hold the mica and tin foil in place. The next thing is to solder a wire to each end of the con- FiG. 115. — Condenser With Soldeked Ends. denser. To do this place the condenser between a pair of smooth boards and screw it up in a vice with one end of the condenser up and above the boards. Sprinkle a little powdered rosin be- tween the ends of the leaves of tin foil and then with a hot soldering iron melt some solder and let it fall a drop at a time on the tin foil. Do not touch the tin foil with the hot iron or it 7 ^ — ^^TTT M SM* will melt away. Soon all the ^T^ ^^^ ^ ends of the leaves will be melted in with the solder, and a firm metal edge will result as shown in Pig. 115. IvTow cut off two pieces of insulated wire about 4 inches long and scrape the ends clean. Lay an end of one of these wires on the soldered end of the condenser, sprinkle on a little rosin and hold your soldering iron on it until the solder runs just enough to hold the wire firmly. Dip the whole condenser in melted paraflBn several times un- til the paraffin has gotten into every crevice and then lay it on a table and put a flait-iron or other weight on it. Make a little wooden box 2| inches wide, 3^ inches long and Fig. 116. — Condenser Com- plete. A- HARD FIBER DISK ■3° "'^Vnut 6- THE FIXED PLATES ASSEMBLED • f li 1 ^SPINDLE A.NUT r »wa5he:« ' n !n ' er, in itm . h Ji ,; Ba , •;» 1 Ka r.a J ""'^^CUP BEARING C-THE MOVABLE PLATES ASSEMBLED adjustinq screw hard fiber bottom D- CROSS SECTION OF ASSEMBUEO* CONDENSER. E:THE VARIABLE CONDENSER COMPLETE Fig. 117. — How The Vakiable Condenser Is Made. 93 THE RECEPTOR 99 ^ inch high on the inside. Drill two holes in the opposite ends of the box and draw the wires through the holes as shown in Fig. 116. Fill the box with melted paraflSn and glue on the top. The Variable Condenser. — This condenser consists of a number of fixed semicircular brass or aluminum plates, and a num- ber of movable semicircular metal plates arranged so that they interleave with each other. By turning the knob the movable plates are moved in or out of the fixed plates and in this way the capacitance of the condenser is varied. For this condenser you will need the following material: (1) two hard fiber disks with holes drilled in them as shown at .4 in Fig. 115; (2) eleven large semicircular fixed metal plates (see B); (3) ten small semicircular movable metal plates (see C); (4) four brass rods f inch in diameter and 3| inches long; (5) ten hexagonal nuts; (6) thirty-three washers -^ inch thick, f inch in diameter and with a | inch hole in them; (7) a knob; (8) a scale; (9) two binding posts, and (10) an | inch adjusting screw. To assemble the condenser, thread the ends of all the rods; hollow out one end of the rod you are going to use for the shaft. Begin by building up the fixed plates and this you do by screw- ing a nut on each one of the support rods, then placing the hard fiber bottom on it, then a washer on each side, then a plate and so on until you reach the top. Next buUd up the movable plates in the same way and when you get to the top, screw on a nut on the rod to hold them firmly in place. Now screw the adjust- ing screw in the bottom hard fiber plate and slip the movable plates between the fixed plates. Next screw the binding posts to the top hard fiber plate and connect one of the fixed plate supports and one of the posts to- gether and then connect the shaft of the movable plates with the other post. This done set the hard fiber top over the ends of the supports and screw a nut on each one. Finally screw a knob on the shaft and your condenser is done. The cross section D shows aU the details of assembly. It is better to have a pointer, which you can make out of tin, and a scale which you can mark ofiF on a piece of paper so that you can see just what you are do- ing. The completed variable condenser is shown at E. 100 THE BOOK OF WIRELESS The Telephone Receiver. — A telephone receiver used for long distance wireless work is formed of two watch-case receiv- ers connected with an adjustable head band so that it can be easily and quickly fitted to the head. The bands are made of strips of spring brass or steel and are either nickel-plated or cov- ered with hard rubber or leather. The ends of the head band are usually slotted and are at- tached to the cases of the receiver by means of a hinged joint, or, better, with a ball and socket joint; this latter kind of a joint gives a greater freedom of movement and allows the ear- piece to be fitted closely to the ear and this helps the operator to hear the faintest sounds. A telephone receiver to work properly with a crystal de- tector should have the coils of its magnets wound to a resistance of 1,000 ohms to 2,000 ohms. Usually the higher the resistance of the magnet coils of a telephone receiver the more sensitive it is, but there are other things which go to make a telephone re- ceiver good, bad or indifferent. With your pair of head telephone receivers you should buy a cord 6 feet long so that you can move freely about when you have them on, as this is a great convenience when you are send- ing and receiving. Wireless telephone receivers cost anywhere from $3.00 to $12.00 a pair and so you must let your pocketbook be the judge of the price you pay. A pair of head telephone receivers is shown in Fig. 118. The Potentiometer (Pronounced po-ten'-she-om'e-ter). — Potentiometer is a big word and means an apparatus for meas- uring electric pressures. It is a word which never should have been used for the variable resistance of a wireless receiving set, since electric pressiu-es, which are set up by the crystal, are not measured but simply varied to meet the needs of the de- tector. But since the word Ls used by all wireless workers, right or wrong, we must accept it and use it too. THE RECEPTOR 101 There are very few crystals used in wireless which need a battery current to make them work. The reason for this is be- cause the high frequency currents set up in the aerial by the incoming electric waves are changed into direct cur- rent and this direct cur- rent is usually large enough to work a pair of telephone receivers with- out using a current from a dry cell. A current from a dry cell will, though, some- times make the signals in the telephone receiver louder than those pro- duced by the current re- ceived by the aerial wire and changed into a direct current by the detector. If now a dry cell is used to supply the extra direct current to the detector and telephone receiver a potentiometer, or variable resistance, should be used so that exactly the right amoimt of current can be had to make the loudest signals. A simple and very good potentiometer can be made on ex- actly the same Unes as the water rheostat which was described in Part II, Chapter I, on page 62, for the sending apparatus. Make a piece of wood 5 inches long, 3^ inches wide and f inch thick as shown in Fig. 119, and drill two holes \ inch in diameter in the center of the circles which show the positions of the binding posts. On the under side of the band cut out these holes to f inch in diameter and to within \ inch of the top Fig. 118. — Head Telephone Rbceiverb. 102 THE BOOK OF WIRELESS as in Pig. 119. [When these are done put on a couple of binding posts. Saw out a support of the same kind of wood and make this 4r| inches long (or high), 3 J inches wide at one end and 1 inch wide at the other end. Screw this support to the end of the base nearest the holes as in Fig. 120. sL_. r WIRE LOWER COPPER ELECTRODE MFIiETE. POTENTIO- METER CONDENSER Fig. 126 and screw them down tight. The exact position of each part is merely a matter of choice, though the tuning coi^ and the detector should be close to the key of the transmitter, as the tuning coil will have to be adjusted very often in order to get the in- coming signals clear and loud in the receiv- er. TELEPHONE RECEIVER Fio. 126. -Plan View of Instruments on TABI.B. The detector should be placed close to the tuning coil on the left or you may set it in front of the tuning coil, as this is also a device which will frequently need adjustment. 106 THE BOOK OF WIRELESS &6NDI Screw into the table on the left of the detector a pair ttt triple binding posts, that is the kind of binding post which has three holes and three set screws for connecting in the wires. Three holes in each binding post are needed, as three wires lead to each post, as will be seen presently. The potentiometer may be placed to the left of the detector with the dry cell to the back, or on the side of it with the switch in front. After all the parts are set on the operating table just where you want them screw them down tight. Wiring up the Re^ ceptor. — To wire up the various parts follow . the wiring diagrams. Figs. 137 and 128. These diagrams are alike except that one has the potentiometer and the other is with- out it. In either case begin by connecting the slider A of the tuning coil, by means of the wire at- tached to one of the rods it slides on, to the groimd. Connect the wire of the slider B with the triple binding post marked X and which is screwed to the table; connect the binding post A of the detector, which leads to the brass well, to the binding post marked X and also connect one end of the telephone receiver cord with the binding post marked X. From the rod of the slider C run a wire to one end of the TELEPHONE RECEIVER Pig. 127. — ^Wiring Diagram of Recep- tion With Potentiometer. THE RECEPTOR 107 condenser and connect the other end of the condenser with the binding post of the detector marked B and which is connected with the phosphor-bronze point as shown in Fig. 100. If the detector is to be used without the potentiometer all CONDENSER HEAD TELEPHONE RECEIVER Fig. 128. — ^Wibinq Diaosam of Receftob With PoTENnoMBTBB. that remains to be done is to connect the binding post B of the detector and the other end of the cord of the telephone receiver with the binding post Z which is screwed to the table ; these con- nections are shown in Fig. 127'. But if the potentiometer is to be used then connect the bind- ing poet B of this device with the binding post B of the crystal detector as shown in the wiring diagram, Fig. 126. Connect the binding post marked A of the potentiometer with the bind- mg post Z and also with one end of the switch. Connect the 108 THE BOOK OF WIRELESS binding post B of the potentiometer to the carbon of the dry cell and connect the zinc of the dry cell to the switch. The receptor is now ready to be adjusted. Adjusting the Receptor. — ^When you adjust the receptor for the first time after wiring it up it is better not to use -the potentiometer and dry cell shunted around the detector as shown in Fig. 128, but to connect the telephone receiver directly to the binding posts of the detector as shown in Fig. 127. The re- ceptor complete and ready for use is shown in Fig. 129. To Adjust the Receptor Without the Potentiometer. — Put on the head telephone receivers and fit the cases closely to your ears. Adjust the detector by screwing the adjustiag screw up and down and changing the position of the phosphor-bronze point on the crystal until you hear a slight crackling sound which means that you have found a sensitive point on the crystal. There are certain parts or spots on crystals that are very sensitive and other places which give no results at all, so the only thing to do is to hunt around and find the best spot. Once you have found a sensitive spot do not move the phosphor-bronze point again, but simply vary the pressure of the phosphor-bronze point on the crystal by means of an adjusting screw, but be care- ful that you do not use too much pressure. Now adjust your tuning coil. If there is a wireless station working near you, this will be a fine experience. Set the sliders B and C close together in the middle of the coil and the slider A near the end of the coil opposite the one to which the aerial wire is attached. Begin to tune by slowly moving the sliders B and C apart and ehoiild you hear the faint buzzing of dots and dashes of some station sending messages move the sliders to and fro until you hear the signals the loudest; then move the slider A until you hear the signals still louder. A very little practice will enable you to adjust the tuning coil so that the signals of any station will ring clear and loud in the receivers, since by moving any one of the sliders one way or 109 110 THE BOOK OF WIRELESS the other over the coil even a trifle, the signals will grow weaJier or stronger and henee you know just which way you should move them. To Adjust the Receptor with the Potentiometer. — ^After you have learned to adjust the detector and tuning coil so that you can get good results, connect in the potentiometer and dry cell as shown in the wiring diagram. Fig. 138. Before closing the battery switch have the copper electrode of the adjusting rod as high as it will go ; now close the switch and begin to screw down the rod; this will be slow work the jfirst time but once you have found the proper distance between the copper electrodes, and you will know this by the strength of the signals, you will not need to change the adjustment very much. In connecting in the potentiometer you must be very careful to see that the current from the dry cell flows through the de- tector in the same direction as the direct current made by the detector from the high frequency currents which are set up in the aerial wire by the incoming waves. If the connections are made as shown and described these currents will flow in the same direction. Cost of Eeoeptob When Bought op Dealers ^ 1 tuning coil — 3 slides $3.50 1 crystal detector 5.00 1 pair of standard 1,000 ohms receivers 4.00 1 fixed condenser 1.00 1 potentiometer (carbon) 1.50 1 dry cell 20 1 baby knife switch 25 2 triple binding posts 30 Total $15.75 "The priees of the different parts of the above receptor are only approximate and you should get prices from a number of dealers before buying. THE RECEPTOR 111 Cost of Receptor When Home-Made Tuning Coil 1 core of wood (turned) $ .20 2 wood cheeks 10 6 feet J-inch. brass rod or tubing 50 6 hexagon nuts 10 1 piece of brass rod for sliders 30 1 phosphor-bronze spring 10 1 pound, enameled wire 1.50 4 binding posts 40 $3.20 The Crystal Detector 1 wood base $ .10 All brass needed except binding posts 50 1 oz. siHcon crystals 25 Rubber handle for adj. screw 15 2 binding posts 20 Screws and nuts 10 Total $1.30 Telephone Receiver (1,000 ohms) $4.00 The Condenser 15 sheets of mica — 2 x 3 inches $ .35 Tin foil 10 Box 10 $ .55 The Potentiometer Wood for base and standard $ .20 Brass for adjusting rod and arm 25 Copper or zinc electrodes 10 Binding posts < 20 Tumbler (glass) 05 .80 Baby knife switch 10 2 triple binding posts 30 Total cost to make receptor $10.26 CHAPTBE III A GOOD AEEIAIi WIRE SYSTEM With a well made transmitter and receptor you should by all means have a good aerial wire system. The term aenal wire system means the aerial wire, the ground and that part of the tuning coil which is con- nected with them. To be able to send and receive messages over the longest possible dis- tance the aerial wire must be high- ly insulated to pre- vent the high-pres- sure currents used in sending and the feeble currents set up by the incoming electric waves in re- ceiving from leak- ing away. As all the ma- FiG. 130. — Mast — on Top of the Hottsb. terial used in an aerial can be bought at a hardware store, to maie and put up a good aerial is a simple matter. To get a place where the stretch is long enough and where there are two points high enough for your aerial is the hardest part and ia 112 A GOOD AERIAL WIRE SYSTEM 113 this you will probably have a chance to show your ingenuity. No hard and fast rules can be given for this part of the work, as conditions everywhere are different. The best way to get a suitable height is to put up a pole 30 or 40 feet high on top of your house as shown in Fig. 130, mak- ing the total height from the ground something like 60 or 70 feet. Of course a pole or mast need not be used and many boys are doing good work with low aerials, as the one described in Part I, Chapter III, but the higher the aerial the longer dis- tance you will be able to send and receive over. The Horizontal, or Plat-Top, Aerial. — There are many kinds of aerials (see Appendix E) but as all ships and nearly all shore stations have what is called the horizontal, or flai-top aerial — different names for the same kind of an aerial — this is the kind you should make and put up if conditions will permit. This kind of an aerial, which is shown in Fig. 27, Part I, Chapter III, is made up of two or more parallel wires and is supported between two points of about equal height, like the masts of a ship. While a high and a long aerial gives the best results so, too, a large number of wires adds to its sending and receiving power, that is if the wires are not too close together. The wires of an aerial should be at least 2 feet apart and so it will be seen that hot more than three or four wires can be used to advantage as a 7-foot spreader is about as long as it is safe to put up in most places. The aerial should have a stretch of at least 100 feet if a ^ kilowatt transformer is used for sanding, and if you cannot get as long a stretch for your aerial as this then a smaller trans- former, say ^ kilowatt, will give just about as good service and will be much cheaper. Making; an Aerial. — The materials needed to make a good three-wire aerial, which let us suppose is to be 150 feet long, are : 550 feet of alumimun or bronze wire. 2 spruce spreaders 2^ inches in diameter and 5 feet long. 8 No. 6 electrose ball insulators. 114 THE BOOK OF WIRELESS 1 spruce spreader IJ inches in diameter and 5 feet long. 1 spruce spreader 1 inch in diameter and 2 feet long. 6 galvanized iron withes 2^ inches in diameter and hav- ing two eyes. 6 galvanized iron S hooks, 2^ inches long. 2 thimbles, for J inch wire rope. 2 thimbles for f inch manilla rope. 6 brass stops, ^ inch long and J inch in diameter. 6 porcelain insulator tubes, ^ inch in diameter and 3 inches long. 2 tackle blocks, of iron or wood, and Enough manilla rope, f inch in diameter. Kinds of Wire. — ^There are four kinds of wire which may be used for the aerial and these are: (1) galvanized iron wirej (2) aluminum wire, (3) phosphor-bronze wire, and (4) silicon- bronze wire. (1) Galvanized iron wire is not as good as the others for the reason that iron is not a good conductor of electricity; the good thing about galvanized iron wire though is that it is cheap. (2) Aluminum wire is almost as good a conductor of elec- tricity as copper; it is very light, quite strong and is a little cheaper than copper wire. If you use aluminum wire get No. 12 size Brown and Sharpe gauge, which is about i inch in diame- ter. (3) Phosphor-bronze wire is an alloy made of copper and tin with a small amount of phosphorus in it. It is almost as good a conductor of electricity as copper ; it is as tough as wrought iron and does not corrode easily. For this reason it is largely used for aerials. Get it soft drawn and made up of seven strands, each of which is No. 22 Brown and Sharpe gauge. (4) Snicon-bronze wire is much cheaper than phosphor- bronze and is almost as strong. Stranded wire is better for aerials than solid wire, as it has a larger surface, and this makes it a better conductor of high- frequency currents. Soft-draT\Ti wire is much easier to handle A GOOD AERIAL WIRE SYSTEM 115 than hard-drawn wire and this should not be overlooked when ordering. The Spreaders. — Any kind of strong sticks will, of course, do for the spreaders, but it gives a fellow a lot of pleasure to have a good-looking aerial as well as a good working one. k-- 2? Fig. 131. — ^The Spkeader for the Ends. Four spreaders are needed, one at each end of the aerial, one in the middle to keep the wires apart, and a short one for the leading-in wires. Make these spreaders of spruce if you can get this kind of wood, for spruce is light, springy and strong. If you cannot get spruce use hickory, though hickory is heavier than spruce. Make iiie two end spreaders 5 feet long and 3 inches scant in diaiaeter, as shovtm in Fig. 131; make the middle spreader 5 feet long and 1^ inches in diameter, as in Fig. 132, and the leading-in spreader 3 feet long and 1 inch in diameter, as shown S^- Fig. 132. — The Middle Spkeader. in Fig. 133. Drill three ^ inch holes in the middle spreader (Fig. 132) and the leading-in spreader (Fig. 133) — a hole in the middle of each spreader and a hole at each end — so that the wires can be slipped through them. The Spreader Withes. — Withes are simply galvanized iron rings with eyes attached to them. Six of these withes are needed — ^three for each of the end spreaders. Each withe should have two eyes as shown in Fig. 134 and have ( n n -mf an inside diameter of 2J inches. (« 2' H Slip three withes on each of the Fig. 133.— Leading-In end spreaders — one for the middle and the other two for the ends. Drill a hole through each withe and drive in a screw to keep it from slipping on the spreader. O) 116 THE BOOK OF WIRELESS The Ball Insulators. — To properly insulate tlw wires from the masts is most important and you will never have a good station unless this is done. SIDE VIEW ^^® insulators generally used for high- grade aerials are made of a patented com- pound and are called electrose insulators. ^ Electrose is almost as good an insulator as END VIEW hard rubber, while it is very much stronger^ With ^ro aS™ ^® °°* afEected by heat or cold, is waterproof, and, finally, it is cheaper than hard rubber. The ball insulators made of electrose and which are used for holding the wires to the spreaders and the spreaders to the masts have eyes fastened to them as shown in Pig. 135. Eight No. 6 ball insulators will be needed — ^four at each -iHhr: end of the aerial. <^ Mp Other Hardware Needed. — To complete ^^^ I'ss — EtEc the list of materials for your aerial buy six trosb Ball In- galvanized iron S hooks, 3J inches long, as stjlatob. shown in Pig. 136, and connect the ball insulators with the rings of the withes on the end spreaders as shown in Pig. 137. Next make, or have made, six brass stops, each of which is ^j, 21^~h' - formed of a piece of brass rod f inch in di- ameter, ^ inch long and having a i inch hole drilled through it so that it will slide on the Fig. 136.— S Hook, ^^e; also drill a hole, tap it and fit in a short machine screw so that the stop can be screwed tight to the wire when it is put in position. One of these stops is shown in Pig. 138. A pair of the stops are put on the opposite sides of the middle spreader to prevent it from slip- ^rlhe ping out of place on the wires. *14)J^ Steel Wire.— Get 20 feet of stranded Fia-^ 137.— S Hook steel wire f inch in diameter — 10 feet for Insulator With each end of the aerial. Stranded steel wire Withe. is used at the ends of the aerials instead of manilla rope, as it does not stretch in wet weather. Cut the wire into four lengths and have two pieces 7 feet long and two pieces 3 feet long. A GOOD AERIAL WIRE SYSTEM 117 Tiiimbles. — Thimbles are galvanized iron side v iew ovals with srrooves formed ia them (see Fiff. I^! — ®1 ^J^ Ej^D VIEW 139) and around which the steel wire or ma- nilla rope is looped and fastened. Four thim- Spreader Stop. bles will be needed, a large one and a small one at each end of the aerial. The small thimbles have i inch grooves in them so that the stranded steel wire will lay in snugly, while the large ones have f inch grooves to fit the manilla rope. ^DQEviEw Shackle Bolts. — Shackle bolts are | Fig. 139. — ^Thimble, inch iron rods bent in the shape of the letter U and having eyes formed on the end of the rods so that bolts can be passed through them as shown in Fig. 140. These bolts are used to link the eyes of the insulators at the ends of the aerials with the thimbles holding ^ the manilla rope. ^ C ^ Tackle Blocks. — A tackle block consists ( ( of a grooved pulley on an axle and fitted in a ^dZH^ case of iron, brass or wood having a ring at ^^^- 140. — Shack- j V • -n- -..-. i-E Bolt. one end as shown m Fig. 141. The block is secured to the masthead and by ^-unning a manilla rope, one end of which is fastened to the aerial, through the block and over the pulley, the aerial can be hoisted to the top of the mast and lowered if needs be. The Manilla Eope. — The amount of rope, which should be f inch in diameter, is like the amount of aerial wire, subject to conditions, but you can easily figure out the „ . ™ amount after you have found the height and Block. length oi your aerial. Cut the rope into two pieces of the lengths needed and you are ready to assemble the aerial. Assembling the Aerial. — Begin the work by linking a small thimble — ^it is open at the sharp end — ^through the eye of one of the insulators. Now loop the middle of one of the 7 foot 118 THE BOOK OF WIRELESS lengths of steel wire around the thimble, twisting the end of one of the 3 foot lengths of steel wire around the other wires at the sharp end of the thimble, and wrap the three wires very tightly with some thin, strong steel wire as shown in Pig. 143. Bring the free ends of the wires through the eyes in the withes on the end spreader and twist them around themselves so that there is no danger of their pulling apart. Fix the other steel wires on the thimble and fasten to the remaining end „ ,,„ ^ spreader in the same way. Fia. 142.— JoiNma -xr _l i n j; ■ t THE Steel Wibb. Next loop one end of a piece oi manilla rope around one of the large thimbles and splice it to the body of the rope, if you know how to splice well. If not, lay the end close to the body of the rope and wrap it with two or three layers of fish line which must be put on very tightly. The thimble on the end of the manilla rope is linked into the eye of the ball insulator by means of a shackle bolt. To each of the opposite eyes of the withes on the end spread- ers secure a ball insulator with an S hook. This completes both supports of the aerial as in Fig. 143. ITow cut off three pieces of the aluminum or bronze wire each 150 feet long and lay them parallel on the ground. Slip the ends of the wires through the holes in the middle spreader and draw the wires through imtil the spreader is halfway be- tween. On the wires at each end slip the brass stops and slide these along until they touch the middle spreader. By screwing them to the wires the spreader cannot slip from its position, aa will be seen from the detailed drawing. Fig. 144. Place the finished supports of the aerial close to the ends of the aerial wires, and loop the end of each wire through the eye of an insulator and twist it up tight. This done, cut ofiP a piece of the aluminum or bronze wire long enough to reach from the top of the mast to your apparatus on the operating table. Twist one end of the leading-in wire to the middle aerial wire and at a point far enough away from A GOOD AERIAL WIRE SYSTEM 119 the end spreader so that when the aerial is hoisted to the mast- head the leading-in wire will swing clear of the building. To each of the two outside aerial wires twist an end of a 10 foot length of wire. Slip the free end of the leading-in wire through the middle hole in the leading-in spreader and slide it 143. — InSttiiAted Support fob Aerial Wires. i?i" along until the ends of the shorter wires are reached. Thread these through the holes of the leading-in spreader and twist the free ends around the leading-in wire. The aerial is now ready to be hoisted to the mastheads. Putting Up the Aerial. — The tackle blocks should be lashed to the mastheads with rope, and ropes long enough so that both ends will reach to the ground when the pole is up should be rim through the blocks. All this, though, should be done before the poles are put up on top of the building. 120 THE BOOK OF WIRELESS After the poles are set up and guyed out bind one end of the small rope to the free end of the aerial rope and draw it up and through the pulley block. Keep on pulling the rope until the aerial swings high and taut between the mastheads. & WIRE -E CD 00 o> ■oco » WIRE WIRE ■B -S fr WIRE §- FiQ. 144. — ^Beass Stops on Aekiaxi Wiee. The Leading-ln Insulator. — With an aerial as well made aa the one just described you should keep up the good work and bring the leading-in wire of the aerial through the wiadow-pane if possible. The best way to do this is to get an electrose leading-in insulator which is largely used by the big wireless companies. [This leading-in insulator is 5 J inches long, If inches in diameter at its large end and 1 inch in diameter at its shank. The shank, which is f inch long, is threaded and a brass ring If inches in A GOOD AERIAL WIRE SYSTEM 121 diameter and ^ inch thick is threaded on the inside so that it can be screwed on to the shank as shown in Fig. 145. Cut a hole If inches in diameter in a window-pane nearest your leading-in wire and put the insulator through the hole with the shoulder of the insulator up against the glass; now screw the threaded brass ring on to the shank on the other side of the pane of glass. Thread the end of your leading-in wire through the hole of the in- sulator, draw it inside the room and connect it with one side of the aerial switch. The way in which the end of the wire is led through the leading-in insulator is shown in Fig. 146. The lightning Switch.— To protect the sending and receiving apparatus from light- ning, a lightning switch should be used and in some places the Fire Underwriters require them. The switch is simply a double-throw, sin- gle-pole knife switch as shown in Figs. 147 and 148. It is placed on the outside of the building close to the leading-in insulator. A knife switch of this type mounted on a porcelain base can be bought about as cheaply as one can be made; however, if you want to make the switch yourself get a piece of slate or marble for the base about 3 . inches wide, 10 inches long and | inch thick. Drill twelve holes i inch in diam- eter in the base for the screws as shown in Figs. 147 and 148. Now cut from a sheet of brass it inch thick sis pieces 1 inch long and IJ inches wide and bend these over in a vise so that an angle plkte is formed as shown in Fig. 149. Drill two ^ inch holes through the base of each of these angle plates so that they can be screwed to the slate, or marble base. In two of these angle plates drill | inch holes through the part marked contact to form a hinge for the contact blade. Screw all of these angle plates to the slate, or marble base. Fig. 145. — Lbad- iNQ-iN Insula-' TDK. 122 THE BOOK OF WIRELESS Fig. 146. — Leading-in Insulator Through Window. Next make a contact blade of a strip of brass 7 inches long, I inch wide and ^ inch thick. Drill a hole i inch in diameter. I" «■ 10" >■ ^^:::^ « U:-1-^ a ® |(S ®| Fioa 147 and 148. — Top and Side Views op Lighting Switch. A GOOD AERIAL WIRE SYSTEM 123 t inch from each end and a third hole 1 inch from one of the ends. Turn a handle of hard wood 3 inches long and make it 1 inch in diameter at one end , and taper it down to f * inch at the other end and saw a slot in the small end 1^ inches deep. Place the end of the contact blade with the two holes in it in the slotted han- dle and drill two holes through the wood ex- actly in a line with the holes in the blade. This done put in a couple of screws to hold it tight. This is clearly shown in Figs. 147 and 148. Put the other end of the blade between the middle angle plates, put a screw through the holes, slip on a washer and screw on a nut and your lightning switch is finished. Fig. 149. — ^Angle Contact Plate. L i. ■A Top View op Anchor-Gap. The lightning switch is fastened to the outside of the house with long screws passing through the base and porcelain insula- tors. The Anchor-Gap. — An anchor-gap is merely a very small spark-gap and is used to connect one of the ends of the sending 124 THE BOOK OF WIRELESS timing coil with the aerial when messages are being sent and to cut oif the sending tuning coil from the aerial when messages are being received. The purpose of an anchor-gap is to prevent the high-fre- quency currents set up by the incoming electric waves from flowing into the transmitter and being wasted there in doing useless work. To make a simple anchor-gap get a base of slate or marble, or of very dry, hard wood, 4 inches long, 2 inches wide, and ^ or f inch thick, as shown in Fig. 150. On inch from each end and in the middle of the base drill a ^ inch hole. Drill Fig. 151. — ^Anchor-Gap Compuete. these holes out to ^ inch in diameter on the bottom of the base and ^ inch through. Mount two double binding posts on the base as shown in the cuts. Take two brass rods ^ inch in diameter and thread one end of each one and sharpen the other end. On the threaded ends of the rods screw two handles of wood, or hard rubber, ^ inch in diameter and 1 inch long. It is shown complete in Fig. 151. The anchor-gap is screwed to the wall and the leadiag-in wire of the aerial is connected with one of the binding posts. The other binding post of the anchor-gap leads to one of the clips of the tuning coil of the transmitter, all of which is clearly shown in Fig. 88. The Aerial Switch. — An up-to-date aerial switch which is so arranged that the transmitter cannot be operated when the A GOOD AERIAL WIRE SYSTEM 125 receptor is connected to the aerial, thus preventing burn-outs, is the next and last piece of apparatus needed for this set. All of the ■woodwork of the aerial switch should be made of thoroughly seasoned hard wood, though the base may be made of pine or some other kind of soft wood. Make the base 9-J inches long, 5 inches wide and 1 inch thick. On top of the base screw a strip of wood 8J inches long, 3 inches wide and ^ inch U-1^ TO RECEIVER BINDING POST TO GROUND TO MAIN LINE CURRENT -TT STRIP ^ i/ BINDING POST FOR AERIAL BASE -9}i" Fro. 152. — ^Base and Contact Sxjppobts foe Aerial Switch. thick and screw a standard of wood &^ inches high, 3 inches wide and 1 iaeh thick at the end of the base as shown in Fig. 152. Cut out two contact springs from a sheet of brass about ^ inch thick and make these springs 2 inches long and J inch wide and bend out the ends a little, as shown in Pig. 153, to make a good contact. Screw these springs to the opposite sides of the wood standard, \ inch from the upper end, with wood 126 THE BOOK OF WIRELESS screw binding posts and to keep them from dropping down put a small wood screw in each side. Now cut out two more contact springs f inch long and ^ inch wide, bend out the ends of these as you did the others and screw them to the strip of wood f inch from the front end with wood screw binding posts as shown in Fig. 153. Cut out two brass plates for hinging the lever and make these f inch long and ~^^. ^ -5Js« Fig. 153. — Contact Lever for AShial Switch. 'f inch wide, round ofE the edges at one end and drill a ^ inch hole through the ends that are rounded off. DriU holes in the other ends and screw these hinge plates to the strip of wood f inch from the end which is nearest the standard with a pair of wood screw binding posts. Make a lever of hard wood 8| inches long, 2 inches ivide and 1 inch thick. Eound off one of the ends as shown in Fig. 153 and have a ^ inch hole f inch deep in the other end. Have a wood handle turned 3^ inches long, 1 inch in diameter at one end and tapering down to ^ inch in diameter, f inch from the other end, the rest of the way down being ^ inch in diameter. Smear the small end of the handle with glue and force it into the hole in the end of the lever. Screw a strip of brass ^ inch vride to the lever one inch from the top and around it on three sides as in Fig. 153 ; this is to make contact with the front springs on the strip of wood. Cut two strips of brass 5^ inches long and ^ inch wide and drill three ^ inch holes in each strip — two holes f inch from the A GOOD AERIAL WIRE SYSTEM 127 ends and one hole in the middle. Countersink these holes and then fasten the strips to the opposite side of the lever vdth ^ inch flat-headed wood screws through the upper and middle -9H"- FiG. 154. — Side View of Aerial Switch. holes, and drive the screws in flush with the strips. This com- pletes the contact lever and all that remains to be done is to set it in between the brass hinge plates, as shown in Pig. 154, and then put in a round-headed brass wood screw | inch long on each side. 128 THE BOOK OF WIRELESS Since one of the hinged plates is connected with the ground and the other one with the aerial when the lever is thrown to the vertical position — ^that is, up — and the brass strips make contact with the upper springs, the aerial and ground wires are connected with the receptor. On the other hand when the lever Fig. 155. — Aerial Switch Complete. is thrown to the horizontal position — that is, down — ^the strip of brass around the top of the lever will make contact with the springs on the wood strip and this will close the power circuit which supplies current to the transformer as the plan view. Fig. 86 and Fig. 87, shows. Fig. 155 shows the aerial switch complete. A Good Ground. — A good ground is just as important a part of a wireless station as a good aerial. When we speak of the ground in wireless we mean the place where the aerial wire system is connected with the earth. A good ground is one where there is little or no resistance between the earth and the wire which connects with it, and hence, the high-frequency currents can flow freely into s^nd out of the earth. o O 1^ M 129 130 THE BOOK OF WIRELESS To obtain a ground in the city the easiest and therefore the usual way is to connect the ground wire with the water or gas pipes, or both, but a better ground may be had by burying sev- eral large sheets of metal deep in the damp earth. Any kind of metal in sheet form will do for a ground, as zinc, copper or galvanized iron. Zinc and copper make the best groimds because they are good conductors of electricity, but gal- vanized iron works very well and is very much cheaper. For the set I have described the ground should have at least 50 square feet of metal in it and if you can increase this to 100 feet so much the better. To make a ground take ten sheets of zinc, copper or gal- vanized iron say 2 feet wide and 3 feet long. Cut two of these metal sheets lengthwise, into strips, 6 inches wide. Lay the remaining eight metal sheets flat on the floor with their edges together and lay six of the metal strips on top of them as shown in Fig. 156. Now drill twelve holes through each of the pairs of metal strips and the metal sheets and rivet the strips to the metal sheets so that all the metal sheets are joined together. Next solder the metal strips to the metal sheets on the edges where the letter S is marked in Fig. 156 and then solder the ends of three pieces of bare copper wire No. 4 Brown and Sharpe gauge to the strips on the sheets and solder the other ends to a metal strip 3 feet long. From this metal strip run a No. 4 copper wire. Brown and Sharpe gauge, to youj operating table where it is connected with the aerial switch. This wire does not need to be insulated but can be fastened to the side of the house with double-pointed tacks, cleats or in any way that is the easiest. Putting Down the Ground. — Dig a trench 3 feet wide, 9 feet long and 8 feet deep in soil that is as moist as possible. Fill the hole with water. Let the metal sheets down carefully untU the lower edge rests on the bottom of the trench. Fill in the hole with earth and see that the metal sheets are kept in the middle of the trench; this is done by throwing a A GOOD AERIAL WIRE SYSTEM 131 shovelful of earth first on one side and then on the other of the metal sheets. Enn water on top of the ground as often as you can and you will have what is called in wireless language a good ground. Connecting the Transmitter and Receptor with the Aerial and Ground. — Having all the apparatus finished and set in place on your operating table and having the aerial wire put up and the ground plate put down, everything is ready for making the final connections. Place the aerial switch between the transmitter and the re- ceptor, as shown in the plan view, Fig. 157, and set it near the front of the table as it will be constantly in use changing the aerial from the transmitter over to the receptor and back again. Screw the base of the switch to the table so that it cannot move. iThe anchor-gap sho ild be screwed to the wall where it can be seen and yet where it will be out of the way. The plan view. Pig. 157, not only shows how the instru- ments are placed on the operating table but it shows how they are connected up by means of the binding posts. The wiring diagram. Fig. 158, shows the actual connections of all the wires so that you can follow the current from the time it is taken off the power circuit until it reaches the aerial wire system, and from the time it is received by the atrial wire system until it is changed into sound waves in the head telephone receiver. The heavy black lines show the power circuit and the light lines show the high-pressure and high-frequency circuits. Now connect the end of the leading-in wire of the aerial with the hinged support of the aerial switch marked A. Con- nect the end of the ground wire with the other hinged support of the aerial switch marked B. To the hinge A, or at some part of the leading-in wire of the aerial before it reaches the lead- ing-in insulator, solder on a piece of wire and lead it to one side of the anchor-gap, and connect the other side of the anchor- gap with the clip A of the sending tuning coil. Connect the binding post D of the sending tuning coil with tiie hinge B of the aerial switch, or with some part of the ground dVO-yOHONV nVlb3V Ol HOXIMS o o EH a g o 1^ o o w o CQ < a P5 o 8 mao Aaa «> 132 A GOOD AERIAL WIRE SYSTEM 133 wire before it passes through the window-sill to the outside as shown in Figs. 157 and 158. Next connect the contact spring E of the power circuit switch with the contact spring ¥ of the aerial switch and connect the binding post G of the key to the contact spring H of the aerial switch. The binding post D of the receiving tuning coil is connected with the contact spring I of the aerial switch and the slider A of the receiving tuning coil is connected with the contact spring K of the. aerial switch. When all these connections are made the apparatus is ready for sending and receiving messages. Operation of the Sending and Receiving Apparatus. — We will begin by supposing you are going to send a message. First throw the lever of the aerial switch down when the brass band on top of the lever will make contact with the springs P and H of the power circuit, in which the primary of the trans- former and the key are placed. Of course if the key is not closed the circuit wiU still be open, but the circuit is otherwise closed by the aerial switch and the power switch. Now when the key is operated, the transformer changes the low-pressure current of the power circuit into high-pressure alternating currents which charge the Leyden jar condenser. When the condenser is charged it discharges through the spark- gap and this sets up high-frequency currents in the tuned closed circuit formed by the condenser, the tuning coil and the spaxk- gap. These high-frequency currents surge up the wire at A of the tuning coil, through the anchor-gap and to the aerial and back again through the anchor-gap and tuning coil to D and thence to the ground, which together forms a tuned open circuit. Suppose, now, you have sent your message and you want to listen4n. Throw the lever of the aerial switch up into contact with the contact springs I and K. When this is done you will see from the plan view. Pig. 157, and the wiring diagram. Fig. 158, that the power circuit is broken at the contact springs P and H; hence even if you forget and try to send a message and begin working the key when listening-in no harm will come of it. The purpose, then, of having the aerial switch break the 134 k GOOD AERIAL WIRE SYSTEM 135 power circuit is to prevent the sending apparatus from being operated while the receiving instruments are connected with the aerial and ground, and so preventing burn-outs and perhaps a lot of other damage. But when the lever of the aerial switch is up the receiving tuning coil is connected directly with the aerial and ground wires, through the contact springs I and H. The high-frequency currents set up in the aerial wire by the incoming electric waves cannot flow into the transmitter, for the break in the circuit formed by the anchor-gap prevents the feeble current from jumping across and flowing this way, so that all of the current must flow through the receiving tuning coil. It will be seen, then, that the sending tuning coil is con- nected with the ground wire both when sending and receiving. This does not matter in the least when receiving, for the cur- rents which flow into the transmitter when you are receiving by way of the ground wire only add to the capacity of the ground, and this helps rather than hinders. When the high-frequency currents from the aerial wire surge through the receiving tuning coil and to the ground, the current also flows through the closed circuit which includes the tuning coil, the condenser and the detector. The crystal detector changes the high-frequency currents into a direct current and this feeble direct current flowing through the magnet coils of the telephone receiver sets the diaphragm to buzzing and the ear reads off these sounds as dots and dashes. If a dry cell and a potentiometer are used with a crystal de- tector to strengthen the signals, you must take care to have the current from the dry cell flow in the same direction as the direct current produced by the detector. Otherwise the signals will be weakened. When you are through operating, throw the aerial switch halfway between the upper and lower contact springs, throw off the power switch and, if you are to be gone for any length of time, throw the lightning switch outside the window so that the aerial is connected direct to the ground. CHAPTEE IV TUNING TRANSMITTEES AND EECEPTOES Mechanical Tuning. — If you will tie two pendulums to a string stretched between two supports and set one of the pendu- lums swinging you wiU have a very good demonstration of tuning and what tuning means in wireless telegraphy. The etriag which is stretched between the supports should be about two or three feet long and not too tight. Take two marbles of the same size, say glassies, and fasten a piece of striag 12 inches long to each of them with sealing wax. Tie the free ends of the strings about 12 inches apart to the stretched string as shown in Fig. 159. We will call the left- hand pendulum the transmitter and the right-hand pendulum the receptor, and mark them A and B. If, now, you set the pendulum A to swinging, the other pendulum, B, will soon begin to swing also, the energy of pendulum A being transmitted, or carried, along the stretched string to the pendulum B. Now make another pendulum using a marble of the same size as before, stick a piece of string 9 inches long to it and fasten the free end of the string to the stretched striag between the pendulums A and B. Set the pendulum A to swinging again and you will see that while the pendulum B will swing as before, the short pendulum — ^which is not in tune with the other ' — ^will remain quiet. Finally lengthen the striag of the middle pendulum until it is 15 inches long and tie it to the stretched string. Set the pendulum A to swinging once more and again you will find that while the pendulum B swiags in response to it the long pendu- lum will remain still just as the short one did. 136 TUNING TRANSMITTERS AND RECEPTORS 137 It must be dear, then, that the length of the strings and the size of the marbles are the things which control the swing- ing of the pendulums, or, as we would say in wireless, these are the factors which determine their periods of oscillation. V\. • B Fig. 169. — ^A Pair of Tuned PendtjiiUMS. Slectrical Tuning. — ^Another simple experiment which shows exactly how electric circuits are tuned can be easily made if you have a small induction coil and a pair of Leyden jars. Take two Leyden jars of the same size, or capacity, as it is called, and set them a foot or two apart on a weoden base as shown in Fig. 160. Cut off two pieces of copper wire, No. 4 Brown and Sharpe gauge, each 18 inches long, bend these wires and fix them to a wood support (not shown in the cut) so that one end of one wire makes contact with the tin foil inside the Leyden jar A and one end of the other wire makes contact with the tin foil on the outside of the jar. Bend the wires over to form a spark-gap B, J^ inch long and round off the ends of the wires with a file. Cut off two more pieces of No. 4 Brown and Sharpe gauge copper wire 20 inches long and bend these as shown at C, Fig. 160. Fasten these to a wood support and have one end of one of the wires make contact with the tin foil inside the Leyden 138 THE BOOK OF WIRELESS jar and the other end make contact with the tin foil outside the jar as beiore. Bend over the free ends of the wire so that tbey will be about 3 inches apart and parallel for about 10 or 12 inches. Stick a strip of tin foil, one end of which is pointed, to the tin foil inside of the jar C and bend it over the top of the jar and down until the pointed end conies to within ^ inch of the outside tin foil as shown at D. Bend the ends of a piece of E Fig. 160. — ^A Pair op Tuned Letdbn Jaks. copper wire 3^ inches long and slip it between the parallel wires. If, now, you will charge the Leyden jar A with an induction coil it will discharge across the spark-gap B, and if the circuit which includes the Leyden jar C is in tune with the circuit A, that is if the electrical dimensions of the jars and the wires of both circuits are exactly the same, then the circuit C will re- spond to the high-frequency currents, or electric oscillations, as they are called, of the circuit A and sparks will jump across the little spark-gap at D of the circuit C. If when the sparks jump across the spark-gap B of the trans- mitting circuit and sparks do not jimip across the little gap D of the receiving circuit you will know that the circuit C is not in tune with the circuit A, but you can easily put them in tune by moving the wire slider E one way or the other on the parallel wires when you will find a place where the jar C will spark across the gap D. Then you wiQ know that the circuits are in tune. From this simple experiment you will learn many things TUNING TRANSMITTERS AND RECEPTORS 139 about wireless in general and tuning in particular which will be of use to you in the operation of your station. Electric Oscillations. — In making the experiment with the pendulums you will have noticed that a short pendulum swings, or oscillates, very fast while a long pendulum oscillates slowly, and this is also true of a circuit of small and large electrical dimensions in which electric oscillations surge. Just as the length and size of a pendulum governs the time of its swings, or its period of oscillation as it is termed, so the electric oscillations surging in a circuit will be as fast or slow as we want them, that is if we make the circuit electrically small or large. This sounds like magic but it is really very simple. It is done in this way. Just as a pendulum has length, breadth and thickness so every electric circuit has what we may call three electrical dimensions or properties, and these are called resistance, capacity and inductance, and by varying these three things we can make the electric oscillations as fast or as slow as we want them, nearly. Resistance. — If you try to kindle a fire like a South Sea Islander, that is by rubbing a stick of hard wood on a block of soft wood you will notice that the stick wiU not slide over the block very easily and this is caused by friction. If you put soap on the block the stick slips over it with little effort, for soap lessens the friction. When a current flows through a wire it is opposed by some- thing that is very much like friction and this is called the resistance of the wire. Copper wire offers less resistance, or friction, to the passage of an electric current than any other metal except silver and this is the reason copper is used for conductors of electricity. In wireless the resistance of the vrires need not trouble you, for electric oscillations stick to the outside of the wires and if the wires are large and every joint and contact is well made there is very little resistance to overcome. In the sending cir- cuit the spark-gap must not be too long or the electric oscilla- tions wiU meet with a high resistance due to the air and the 140 THE BOOK OF WIRELESS currents will not pass. As far as timing is concerned you need not bother with the resistance of the circuits. Capacity. — A gallon bucket will hold just four quarts and jio more, but there are some contrivances which are never full Tintil they burst. If you force gas into a rubber bag you cannot eay it is full until it has reached the point where it explodes. There are devices made for holding electricity but they are neither buckets nor gas bags. To hold electricity a condenser, with whose construction you are acquainted, is used, and a con- denser is like a gas bag in that it is never full until the point is reached where the current which charges it breaks it down. Different from fluids and gases, a charge of electricity always sticks to the outside of a sheet of metal and hence a sheet of tin foil xfff inch thick will hold just as much electricity as a copper plate 1 inch thick of the same surface area, or size, that is if we neglect the edges. All metals have a capacity for electricity but to get a large capacity into a small space leaves of tin foil separated by sheets of glass or mica or paper are used, and a device of this kind is called a condenser. A condenser will slow down an electric oscillation flowing in a circuit, for the current has to charge the condenser each time before the condenser discharges itself. The size of a condenser has the same effect on an electric oscillation that the length of a pendulum has on its swing; hence, if we want fast oscillations we must use a condenser of small capacity and if we want slow oscillations we must use a condenser of large capacity. Inductance (Pronounced in-duk'tance) . — It takes about •| second for a boy to throw a ball counting the time from the instant he begins to throw until the ball leaves his hand; and if we measured the time it takes him to catch the ball we would probably find it to be in the neighborhood of ^ of a second. It takes time for a street car to get up speed and whea once going it takes time for it to stop. Everything we kaaw of TUNING TRANSMITTERS AND RECEPTORS 141 TO INDUCTION takes time to start and time to stop and electricity is no excep- tion to the rule. Electricity travels 186.500 miles a second, wHeh is just the speed of light — and yet it takes time for it to start and once started it takes time for it to stop. This property of balls and cars and things to resist being moved when at rest and to keep on going when once in motion is called inertia, and the inertia of an electric current is called its inductance. If the electric oscillations are flowing through a straight wire circuit, as in the tuned circuits shown in Fig. 160, it does not take as long for the oscillations to start and stop as it does if the wire is coiled up, for the in- ductance of a straight wire is not nearly as great as that of a coiled wire, but in either case the electric oscillations are slowed down according to the amount of inductance of each. Hence tuning coils are not only the most compact, but they are also the most effective forms of inductances. Open Oscillation Circuits. — In wireless telegraphy the aerial wire sys- tem forms an open oscillation circuit. In a simple open oscillation circuit the gpark-gap is formed between the ends of the aerial and ground wire as shown in Fig. 161. Since no tuning coil or con- denser is used with this open oscillation circuit the inductance and capacity are laid evenly along the straight wires, and both the inductance and the capacity are, therefore, very small. For this reason an electric charge produced by an induction coil on the aerial and ground wires in the small transmitter described in Chapter I, Part I, and which sets up the oscillat- ing currents, is very small ; as these currents are rapidly changed COIL TO INDUCTfON COIL Fig. 161. — Non-tuned Open Obcillation CntcuiT. 142 THE BOOK OF WIRELESS into electric waves the current only makes two or three swinge* or oscillations, before it is entirely gone, or damped out, as it is termed, as shown in Fig. 163. After these electric oscillations are damped out, or changed into electric waves, the aerial and ground wires are agaia charged by the induction coil, another spark takes place and two or three more oscillations suige in the aerial wire, and so on. A straight aerial w'i r e system sends out electric waves which are about four times the length of the aerial, and since there are neither tuning coils nor condensers connected with it the length of the electric wave which it sends out depends entirely upon the length of the aerial wire itself. Closed Oscillation Circuits. — A pendulum which makes Fig. 162.- -Steonglt Damped Oscil- lations. TO TRANSFORMEB, UI to z UJ a u / / i^» TO TRANSFORMER. fFiG. 163. — Tdned Closed Oscillation Gibcuit. ^ TIME A-STRONGLY DA^JPED OSCILLATIONS ^"'"" ^ ^ B-TIME INTERVAL BETWEEN DAMPED OSCILLATIONS C-UNPAMPED OSCILLATIONS FiQ. 175. — Oscillations op a Spark Dischabge. A aad B show Oscillations Set Up by a Spark Discharge. C shows Os- cillations Set Up by an Arc and a Vacuum. Bor dry battery Fta. 176.- i|i|i|i|i|i|i|i|i|iH S or dry cell battieiy -Dbtelopment of the Three-Electrode Vacuum Tube Detector. 159 160 THE BOOK OF WIRELESS in the foregoing chapters the latest and best sets use a vacuum tube detector,^ as it is called. The vacuum tube detector is far su- perior to the crystal detector, for it needs (1) very little adjustment, (2) it works imiformly, and (3) it is much more sensitive than the latter. What the Vacuum Tube Detector Is. — ^You know, of covu-se, that if an incandescent lamp has its filament broken a current will not flow through it. If, however, it were possible to heat one or both of the ends of the filament red or white hot, then the current would flow through it and bridge the gap. Since the filament is in a bulb from which the air has been pumped out you may wonder how it would be possible to perform this experiment. There are several ways of doing it, but an easy way to prove it is to seal an unbroken filament in the bulb with its ends projecting through the bottom and a little metal plate sealed in the bulb with a wire attached to it and the free end brought out through the top as shown at ^ in Fig. 176. Since all vacuum tube detectors and amplifiers use 6 volts to heat the filament we will suppose that this one also does, so con- nect a 6-volt (that is, a 3-cell) storage battery, called the A battery in wireless, to the filament, when it will heat it to brilliancy, as the operators say. Now connect the — or negative electrode of the battery to one post of a galvanometer and the other post of this to the negative or zinc tap of a 22§ volt dry battery, called the B battery, and the positive or carbon tap of ^his to the metal plate of the tube, as shown at B. You will now find that a cur- rent is flowing in the plate circuit which shows that it must be passing through the gap between the filament and the plate. This phenomenon was discovered by Edison many years ago and it is still called the Edison effect. A dozen years or so ago J. A. Fleming found that the Edison two-electrode tube rectified oscillating currents just as a crystal detector does, and hence, like the latter, it could be used as an electric wave detector. He also fojmd that by keeping the plate charged with positive electricity its sensitiveness was greatly in- £ S e ^ I jrri "iiii, I vt f 00025 MFD \tw*X ^GRIDLEAKj A^ ftTOZMEg OHMS M WiiSif C, Wiring Diagram for a Simple Regenerative Receiving Set. and the variable contact of it to the positive electrode of the A battery. Finally connect the variable condenser across the sec-, ondary of the tuning coU and you are ready to tune in either ama- teur stations that work on a 200-wave meter or less or broadcasting stations that send out on waves of from 350 to 400 meters. A Simple Armstrong Regenerative Receiving Set. — Not 164 THE BOOK OF WIRELESS only can a vacuum tube be used as a detector of electric waves but it will also act as an amplifier and, curiously enough, it will act as a detector and an amplifier at the same time, provided a part of the oscillating current is fed back through the tube. This interesting and useful discovery was made by E. H. Armstrong in 1915. By using the Armstrong regenerative feedback, or some modification of it, the vacuiun tube will have its sensitiveness increased manjHFold, and nearly all the good receiving sets are now provided with it. For this receiving set you will need (1) a tuning coil that has three separate coils on it, namely, (a) a 'primary, (b) a secondary, and (c) a tickler, as the third coil is called. This tuning coil can be in the form of a loose coupler having its primary coil fixed, its secondary coil sliding over it and its tickler coil sliding inside of it, or it can be formed of three flat coils, called spider-web coils as shown at A in Fig. 178, or honeycomb or other compact coils can be used. These coils can be bought ready wound, the smallest having a range of wave lengths from 180 to 400 meters with a .001 microfarad variable condenser while the next size will give you a range of waves from 180 to 1,000 meters with a variable condenser of the same capacitance. You can then mount them so that they will swing close to and away from the primary and so vary the coupling. Besides the tuning coils you must also have (2) a .001 mfd. variable condenser; (3) a .00025 mfd. fixed condenser, and (4) a grid leak, see B, of 1 rnegohm resistance. You will also need (5) an A battery; (6) a rheostat; (7) a detector tube; (8) a B battery, and (9) a pair of head-phones all as described for the preceding re- ceiving set. To wire up the set connect one end of the primary coil, which is the fixed coil, to the leading-in wire of the aerial and the other end of the coil with the ground as shown at C in Fig. 178. Now connect one end of the secondary coil with one side of the fixed condenser and the other side of this to the grid of the detector, and shunt the grid leak around the condenser. Connect the other end of the secondary coil to the negative, or zinc, tap of the B bat- A-WIRIN&D^IAGRAM OF AVARIOMETER. B-THE VARIOMETER COMPLETE A and B show the Variometer. UJ i C, A Graphite Potentiometer. 2MEG0HMS ^j^ D, A Regenerative Receiving Set with Variometer. Fig. 179. — ^Regenerative Rbceptok with Variometbe. 165 166 THE BOOK OF WIRELESS tery and the positive, or carbon, tap with one of the terminals of the head-phones. Connect the other tenninal of the latter to one end of the tickler coil and the other end of this to the plate of the detector. Next connect one terminal of the filament with the wire con- necting the secondary coilj,with the B battery, and connect the other terminal of the filament with the sliding contact of the rheostat; then connect one end of the rheostat with the positive electrode of the A battery; last of all, connect the negative elec- trode of this with the other terminal of the filament and you are ready to tune in for amateur or broadcasting stations. A Regenerative Set with Variometer. — ^A variometer is a kind of tuning coil in which the primary coil is fixed and the sec- ondary coil is mounted in the turns at right angles to it. Further one end of the primary is connected to one end of the secondary coil and it has no sliding contacts or other means of varying the inductance of the primary and secondary coils, but tuning is ac- complished solely by varying the coupling between them. The variometer consists of a fixed primary coil wound on a hollow spherical shell and a movable secondary coil which is likewise wound on a spherical shell; the latter is mounted on a spindle which is pivoted in the hollow shell and to this is fastened a knob and a pointer while a scale is mounted on the fixed coil or on a panel so that the relative positions of the two coils can be gauged. The advantage of using a variometer is that the receiv- ing set can be tuned very sharp. The way the coils are connected together is shown at .4 in Fig. 179 and the variometer complete atS. To get the best results with a vacuum tube detector the poten- tial or voltage of the plate must be very carefully adjusted and to do this a -potentiometer is used. A potentiometer best suited for this work consists of either a semicircle of high resistance graphite on which a movable arm makes contact as shown at C, or a coil of high resistance alloy wire wound on a cylinder on which a slider makes contact as in a tuning coil. The ends of the graphite, or coil, are connected with the positive and negative electrodes of the A VACUUM TUBE RECEIVING SETS 167 battery while the sliding contact is usually connected with the ninth negative tap of the B battery; it then delivers a current of 18 volts and this with the current from the A battery gives a total of 24 volts, which may be cut down to the exact amount required. For this set you will need (1) a loose coupler; (2)^a variometer; (3) a .001 mfd. adjustable condenser; (4) two .0005 mfd. adjustable condensers; (5) a .001 mfd. fixed condenser ; (6) a 2-^megohm grid leak resistance; (7) a grid coil; (8) a tube detector, which also acts as an amplifier; (9) an A battery ; (10) a rheostat; (11) a S battery; (12) a potentiometer, and (13) a pair of head-phones, or an amplifier can be connected in instead. In wiring up the parts begin by connecting the leading-in wire to one end of the primary of the loose coupler; the other end of this to one side of the .001 mfd. adjustable condenser and the other side of the latter to the ground as shown in the wiring dia- gram at D. Then connect one end of the secondary of the loose coupler to one side of one of the .0005 mfd. condensers and the other side of this with the grid of the detector and shunt the grid leak around the condenser. Next connect the other end of the secondary coil with one end of the grid coil and connect the other end of this with one terminal of the filament of the tube. Shunt the other .0005 mfd. variable condenser across the grid circuit between the grid leak and the grid coil. This done, connect the positive electrode of the A battery to the terminal of the filament that is connected with the grid coil and connect the negative electrode to one post of the rheostat and the movable contact of the latter with one of the taps of the potentiometer and the other tap of this to the positive side of the A battery. Now connect the sliding contact of the potentiometer with the negative, or zinc, tap of the B battery and the positive, or carbon, tap of this to one terminal of the head-phones; connect the other terminal of the head-phones with one end of the vario- meter and the other end of this with the plate of the detector. Finally shunt the fixed .001 mfd. condenser around the head- phones. In hooking up this receiving set have the wires that 168 THE BOOK OF WIRELESS connect with the detector as short as possible, as this will make it work better. Also where the set is to be used for receiving con- tinuous wave signals, speech, or music you should place a sheet of copper, or shield, as it is called, back of the parts and between the loose coupler and the variometer. A One-Step Vacuum Tube Amplifjong Receiving Set, with Crystal Detector. — ^If you are using a crystal detector set and want to amplify the signals of it you can do so by getting the following additional parts and connecting them up as I shall ex- plain farther on: assuming that your crystal detector set includes a loose-coupled tuning coil, a .001 mfd. variable condenser, a crys- tal detector, a pair of head-phones, and a .001 mfd. fixed conden- ser, then all you need is (1) a vacuum tube amplifier with a socket; (2) an adjustable grid leak ; (3) a .001 mfd. fi^ced condenser ; (4) an A battery; (5) a rheostat; (6) a B battery, and (7) a potentiometer. There is no great difference in a vacuum tube detector and a vacuum tube amplifier, and one can be used in the place of the other. But manufacturers of tubes design them so that better results are had by using the tubes for the particular work they have to do, 30 you should always specify the kind of tube you want. In this receiving set the oscillating currents set up by the re- ceived waves are amplified by the vacuum tube amplifier first at radio frequency, that is at the same frequency with which they surge in the aerial wire system; these amplified currents then flow through the crystal detector, where they are rectified, that is, con- verted into pulsating direct currents when they can flow through and will operate the head-phones. In wiring up this crystal detector amplifying receiving set, the aerial and ground are connected to the primary coil of the loose coupler in the usual way as shown in the wiring diagram Fig. 180. Then connect one end of the secondary coil with one side of the fixed condenser and the other side of this to the grid of the amplifier tube. The other end of the secondary coil is connected with one terminal of the filament and to the negative electrode of the A battery. The other terminal of the filament is connected with one end of the rheostat and the movable contact of the latter VACUUM TUBE RECEIVING SETS 169 with the positive electrode of the battery. The variable condenser is now shunted around the secondary of the tuning coil. This done, connect one end of the variable resistance with the plate and the other end of this with the positive, or carbon, tap of the B battery and then connect the negative, or zinc, tap with the 2M£6 o I Tvee. POTE»9fTtoiArr M«lilil»li|)l"lilii Fig. 180.- -WiEiNQ Diagram of Resistance Coupled Amplifier Rbceptok with Crystal Detector. negative electrode of the A battery. Finally connect the metal point of the detector with the end of the resistance that is con- nected with the plate, connect the crystal of the detector with one terminal of the head-phones, the other terminal of the latter with the other end of the resistance and shunt the other fixed con- denser around the resistance. While the potentiometer is not absolutely necessary, still much better results are had when it is used. A Two-Step Vacuum Tube AinpUf3dng Receiving Set, with Vacuum Tube Detector. — ^This set includes a vacuum tube de- tector and two vacuum tube amplifiers. In this case the first tube acts as the detector and the next two tubes as the amplifiers. You can use a single tube and have a one-step amplifier or you can use two or three tubes and have a two- or three-step amplifier, or 170 THE BOOK OF WIRELESS amplifiers in cascade as it is called. With a two- or three-step amplifier you can get stations a couple of thousand miles away with a single wire aerial, or nearer ones with a loop aerial in the house, or use a loud speaker with it, when every one in the room can hear the incoming messages or music. For this receiving set you will need besides the parts described under the heading of a simple vacuum tube receiving set the following additional parts: (1) two amplifying tubes; (2) two rheostats; (3) two .001 mfd. fixed condensers; (4) two B batteries; (5) two grid leaks; (6) two potentiom£ters, and (7) two audio frequency trans- formers. An audio frequ£ncy transformer (see A in Fig. 181), is simply a small iron core transformer that has a primary coil and a secon- dary coil wound on it. As iron tends to choke off the high frequency currents, the first vacuum tube must be the detector and the succeeding vacuum tubes are the audio frequency amplifiers. The connections for the detector circuits are shown in the wiring diagram B, and are the same as those for a simple vacuum tube receiving set, except that instead of connecting in the head-phones at a and b, the ends of the primary coil of the audio frequency transformer are connected with them; then the ends of the sec- ondary coil of the transformer c and d are connected to the grid and to the negative electrode of the A battery. In this way you can connect in as many amplifying tubes and transformers as you wish. Finally at e and / you can connect in either a pair of head- phones or a loud speaker. Connectiag Vacuum Tube Filaments in Parallel. — While I have shown a separate A battery for each of the vacuum tubes at B in Fig. 181, for the sake of making the connections clear you really need to use only one battery. This you can do by connecting the filaments in parallel, as it is called, and which is clearly shown in the wiring diagram at C in Fig. 181. As storage batteries are ex- pensive as well as bulky, this scheme saves money and space as well as a lot of useless wiring. A 40 volt B battery can be used and all of the plates energized by connecting them to it in parallel. Intermediate Wave and Long Wave Receiving Sets.— The VACUUM TUBE RECEIVING SETS 171 receiving sets I have described above will receive waves of from 150 to 400 meters in length so that you can get amateur and broad- A, An Audio Frequency Transformer. B, A Two-Step Vacuum Tube Amplifier Receptor with Vacuum Tube Detector. C, Detector and Amplifier Tube Filaments Connected to A Battery in Parallel. Fig. 181. — Two-Step Amplifier Receptor with Vacuum Tube Detector. casting stations with any of them. If, however, you want to receive intermediate waves, that is, waves up to 3,000 meters in length, or long waves, say up to 20,000 meters in length, which 172 THE BOOK OF WIRELESS are sent out by the big cableless stations of the world, then you will have to use compact coils of the honeycomb and duo-lateral kinds. You can buy these coils already wound for different wave lengths and while the coils are not adjustable you can time them to the wave length you want to receive by means of your variable condenser, which may have a capacitance of .001 mfd., or larger, for waves of whatever length. You can use coils for wave lengths up to 1,000 meters with a small aerial, but with coils for greater wave lengths than this your aerial must be propor- tionately longer and higher. Further, whatever the wave length of the coil you use for the primary in the aerial wire circuit, you should use a coil of the same wave length in the secon- dary circuit. Connecting in a Loud Speaker. — In ordinary telephone conversa^ tion you have sometimes observed that the receiver reproduces the speaker's voice loud enough so that it can be heard several feet away. This is because there is a large current strength flowing through the telephone magnet coils. The simplest type of loud speaker consists of a horn whose small end is fitted to a regular wireless head-phone as shown in Fig. 182;^ in this case the horn amplifies the sound just as it does that of a phonograph receiver. Loud speakers that are designed especially for the purpose are, however, much more powerful and the Magnavox^ is one of the best on the market. It consists of an induction coil, the primary of which is connected with the receiving set where the head-phones are ordinarily connected in. The secondary coil leads up to and Fig. 182.— The Arkat Loud Speaker. • Made by the Riley-Klotz Mfg. Co., Newark, N. J. s Manufactured by Magnavox Company, of OaMand, Cal. VACUUM TUBE RECEIVING SETS 173 is connected with a movable coU and to this the diaphragm of the loud speaker is attached. The movable coil sets over the end of the iron core of an electromagnet and the field coil of this is con- nected to a 6-volt battery. A wiring diagram of this loud speaker is shown at A in Fig. 183 and the device complete at B. TO 6 VOLT BATTERY OlAPHRAM .MOvAbLE B, Wiring Diagram of the Demonstration Wireless Telephone. Fig. 187. — A Demonstration Wireless Telephone Sendxnq Set. in the neighborhood of $75 without the meters and these will cost about $25 more. The 6-Watt Oscillator or Power Tube. — This power tube is made exactly like an amplifier tube only on a larger scale. It takes a current of 10 volts to heat the filament and 350 volts to keep the plate energized. The socket used with this tube is made of porcelain and has four taps. They are shown at A in Fig. 188. A, The Oscillator Tube and Socket. B, Alternating Current Power Transformer. C, Three-Clip Transmitter Tuning Coil. ^ D, Adjustable Aerial Condenser. E, A Hot- Wire Ammeter for the Aerial System. F, A Voltmeter for the Filament Circuit. Fig. 188. — Parts of a 5- to 50-Watt C. W. Wireless Telegraph Sending Set. 188 VACUUM TUBE TRANSMITTING SETS 189 The Alternating Current Power Transformer. — This power transformer is designed to be used with one or more 5-watt oscillator tubes. It has a primary coil wound on an iron core and two secondary coils. The primary is wound to take current from a 50 to 60 cycle source at 102.5 to 115 volts so that you can connect it up direct to your lighting circuit. One of the secondary coils delivers a 10-volt current for heating the filament and the other secondary coU delivers a 350-volt current for energizing the plate. The transformer is shown at B. The Tuning Inductance Coil. — Instead of using a loose coupled oscillation transformer for receiving, the transmitting tun- ing inductance coil is close coupled, or conductively coupled as it is called, that is, the secondary coil is a continuation of the primary coil. It is formed of 25 turns of copper strip about -^ of an inch thfck and f inch wide and is mounted horizontally on a wood base. It has three adjustable clips and a tap fixed to one end and is pic- tured at C. The Aerial Series Condenser. — This is a fixed condenser and has four taps as shown at D. It gives three different capaci- tances, namely, .0003, .0004, and .0005 microfarads, according to the way you connect it up, and it will stand up under a pressure of 7,500 volts. The Grid and By-Pass Condensers. — The5e are plain fixed condensers, of .001 mfd. capacitance, and one is placed in the grid circuit with the key shunted around it and the other two are con- nected across the terminals of the plate secondary coil of the power transformer. Transmitting Grid Leak. — This consists of a resistance of 5,000 ohms with a mid tap so that you can cut down the resistance to 2,500 ohms. It consists of a high resistance wire wound on a beat resisting insulator. It is shown at B in Fig. 186. The Choke Coils. — These are used to keep the oscillations set up by the oscillator tube from surging back through the secon- dary coil of the power transformer. You can make these coils by winding about 90 turns of No. 30, Brown and Sharpe gauge, cotton covered insulated magnet wire on a tube 2 inches in diameter and 2\ inches long. 190 THE BOOK OF WIRELESS The Meters.— A hot-wire ammeter, see E, in Fig. 188, reading from to 2.5 amperes in the aerial is necessary so that you can see A, Wiring Diagram for a 5- or 50-Watt Continuous Wave Telegraph Sending Set. <.^^ .^t^ .#> B, How the Chopper is Connected In. C, A 50-Watt Os- cillator Tube. Fi<3. 189.- - Wiring Diageam op a 5- to 50-Watt Wireless TEliB- GRAPH Sending Set. ■when the circuits are in tune. When the meter gives the highest reading you will know that the circuits are tuned to each other, as well as the amount of energy that is being radiated. A volt- VACUUM TUBE TBANSMITTING SETS 191 meter, reading from to 15 volts, as shown at F in Fig. 188, is needed to show when the voltage of the filament is right and this should be 7.5 volts. How to Connect Up the 5-Watt C. W. Telegraph Trans- mitter. — To hook up the parts begin by connecting your aerial to the hot-wire ammeter and this to the end tap of your tuning coil, marked 1 in the wiring diagram shown at A in Fig. 189. Con- nect tap 4 with one of the ends of the aerial condenser marked a, b, or c, depending on the amount of capacitance you want in the circuit, and then connect the end of the condenser marked d to the ground. Now connect tap 1 of the tuning coil to one side of the grid condenser and the other side of this to the grid, connect one end of the grid leak to one of the posts of the key, and then shunt these around the grid condenser. This done, connect tap 2 of the tuning coil to one of the terminals of the oscillator tube filament; from this juncture bring down a lead and connect it to one end of the 10-volt secondary coil of the power transformer and connect the other end of this secondary to the other terminal of the os- cillator tube filament. Then shunt your filament voltmeter across the ends of the filament secondary coil. You are ready now to connect the plate of the oscillator tube to one end of the choke coil and connect the other end of this to one of the ends of the 350-volt secondary coil of the power trans- former; connect the other end of the latter to one end of the other choke coil and the other end of this to one side of one of the by- pass condensers. Then connect the other side of the latter with one side of the second by-pass condenser and the opposite side of this to the lead that joins the first choke coil with the plate of the oscillator tube between these two elements; this done connect tap 3 of the tuning coil in between the two by-pass condensers. Finally connect the ends of the primary of the power trans- former with the alternating current service wires and you are ready to send out continuous wave telegraph signals, but in order for a receiving station to get them it will have to be equipped with a heterodyne receiving set. A Grid Chopper for the Above G. W. Telegraph Transmitter. 192 THE BOOK OF WIRELESS — In order for any receiving set to get signals from the continuous wave telegraph transmitter I have just described, you will have to put a grid chopper in circuit with the key and grid leak as shown in the wiring diagram at £ in Fig. 189. A grid chopper is reaUy a motor-driven rotary interrupter and breaks up the sus- tained oscillations so that wave trains are set up which are very much like those produced by a spark telegraph set. A so-Watt C. W. Wireless Telegraph Transmitter. — ^A single 50-watt oscUlator tube will deliver enough energy to the aerial so that you can send telegraph signals 500 miles or so while with two 50-watt tubes in parallel you can cover distances of 1,000 miles and over. Like the 5-watt continuous wave telegraph transmitter these 50-watt sets operate on an initial alternating current of 102.5 to 115 volts at 50 to 60 cycles. The Parts You Need. — The parts of this transmitter and the connections are identical with the 5-watt transmitter described above, except that the former are designed and built for utilizing a larger amount of current and transforming it into higher voltages. The 50-Watt Oscillator Tube. — This tube i made just like the 5-watt tube only larger and of a little different shape, as shown at C in Fig. 189, and it takes 10 volts to heat the filament while 1,000 volts are needed to energize the plate. A porcelain socket is also used with this tube. The Alternating Current Transformer. — For a 50-watt os- cillator tube you wiU need a power transformer that has an input of 750 1 watts. The filament secondary coil delivers 10.5 volts between the ends of it while the plate secondary coil delivers 3,000 volts between its ends. This transformer will supply enough current for two 50-watt tubes. In all other respects it is like the one I described for the 5-watt power tube. The Oscillation Choke Coils. — You can make these by wind- ing about 260 turns of No. 30 Brown and Sharpe gauge cotton- covered magnet wire on a paper or glass tube 2j inches in diam- eter and 3| inches long. Other Parts of the Transmitter. — The key, by-pass con- denser, grid condenser and aerial condensers are exactly the same > There are 746 watts in 1 horsepower, and 1,000 watts equal 1 kilowatt. VACUUM TUBE TRANSMITTING SETS 193 as those I described for the 5-watt transmitter, except that the grid leak is made a little larger to take more current, but it has the same resistance. The hot wire ammeter for the aerial wire should read from to 5 amperes and the volt-meter from to 15 volts. These parts are connected up as shown in the wiring diagram at A, Fig. 189. You can use a grid chopper with it (see B, Fig. 189), or not, depending on whether the receiving station has a heterodyne receptor or an ordinary receptor. A s-Watt Wireless Telephone Transmitter. — This wireless telephone transmitter is the simplest type I know of in which an oscillator tube is used to set up sustained oscillations as in the pre- ceding telegraph transmitters. The plate, though, must be ener- gized by -a direct current of 350 volts and this can be had from either a motor-generator^ or by means of an alternating current power transformer, the secondary current of which is converted into a suitable direct current by a rectifier vacuum tvhe. The os- cillations in the aerial are varied, or modulated, as it is called, by a microphone and a magnetic modulator which I shall explain pres- ently. It will send speech or music to a distance of, say, 25 miles. The Parts of a 5-Watt Wireless Telephone Transmitter. — For this transmitting set you will need: (1) a tuning inductance coil; (2) an aerial condenser ; (3) a grid condenser ; (4) grid leak ; (5) two B^watt oscillator tubes ; (6) two 20-^att rectifier tubes ; (7) a blocking condenser ; (8) twofiiter condensers; (9) an oscillation choke coil; (10) a, filter reactor; (11) a 110-volt alternating current power transformer; (12) an a. c. filament voU-^meter ; (13) an aerial hot-wire ammeter; (14) a 6-»oft dry or storage battery for the microphone: (15) a micro- phone; (16) a magnetic modulator, and (17) a switch for the micro- phone circuit. The 110-Volt Alternating Current Power Transformer. — Although the p>ower transformer used for the continuous wave telegraph transmitters described in this chapter has three secon- dary coils, I mentioned only two, as these are the only ones used, but for a wireless telephone transmitter the third secondary coil is connected to a rectifier tube. For a 5-watt telephone transmitter > This consists of a motor driven by 160 volt d. c. or a. c. current direct con- nected to the shaft of a 350 or 1,000 volt d. c. generator. 194 THE BOOK OF WIRELESS get a power transformer with an input of 325 volts. This is shown at B in Fig. 188. The Rectifier Vacuum Tube.— This is a two-electrode vacu- um tube (see A in Fig. 190) and it is used to convert alternating cur- THE RECTIFIER TUBE' THE SOCKET A, Two-Element Rectifier Tube. B, The Filter Reactor. ^' ^^e Microphone Magnetic Fig. 190. — Pabts of a 5- to 50- Watt Wibeless Telephone Sending Set. rent into pulsating direct current. These rectifier tubes, or recti- fier valves, as they are sometimes called, are made so that they will take care of large currents. The rectifier tube you wUl need for a 5-watt oscillator tube transmitter is rated at 20 watts. It is shown at A in Fig. 190. The Filter Reactor. — The purpose of a filter reactor is to VACUUM TUBE TRANSMITTING SETS 195 smooth out the pulsating direct current after it is produced by the rectifier tube. This consists of a large inductance and a number of condensers. A IQO^milliampere filter reactor (see B, Fig. 190) is the kind you want for a 5-watt tube transmitter. The Filter and Blocking Condensers. — All of these are fixed condensers having a capacitance of 1 microfarad each and they are made to withstand potentials of 750 volts. The Microphone. — This is an ordinary carbon telephone transmitter as shown at A in Fig. 187. It can be mounted on a handle, a stand, or an extension bracket, but in any case the dia- phragm must be kept in a vertical position to get the best results. The Microphone Battery. — This can be either four dry cells or a 6-volt storage battery. The latter is the best, since the current does not keep dropping off. The Microphone Modulator. — This is the best scheme for modulating the sustained oscillations set up in an aerial where one or more small oscillator tubes are used. It provides a means for coupling a microphone to the oscillation circuits and does not distort the sound waves which are impressed on the diaphragm (see C, Fig. 190). Other Parts of the Transmitter. — The tuning inductance coil, the aerial condenser, the grid condenser, grid leak, oscillation tube, filter condensers, choke coil, filament volt-meter and aerial hot-wire ammeter are exactly the same as those described in con- nection with the 5-watt telegraph transmitting set. How the Farts Are Connected Up. — Begin by connecting the aerial wire to the end tap of the tuning coil marked 1 in the wiring diagram shown in Fig. 191. Connect the adjustable tap 4 with one of the sides of the aerial condenser marked a, b, or c, depending on the amount of capacitance you want in it; then con- nect the side of the condenser marked d to one of the secondary posts of the magnetic modulator and the other secondary post of this with the ground. Connect the microphone, the 6-volt battery, the switch and the primary coil of the magnetic modulator in series. This part of the system wired up, connect tap 1 of the tuning 196 VACUUM TUBE TRANSMITTING SETS 197 coil to one side of the grid condenser and the other side of this to the grids of the oscillator tube; then shunt the grid leak around the condenser. Next connect tap 2 of the tuning coil to one of the terminals of the oscillator tube filament and from this bring a lead and connect it to one end of the 10-volt filament secondary coil of the power transformer and connect the other end of the filament to the other end of the filament secondary coil. Now connect the ends of the filaments of the rectifier tubes to the ends of the 7.5 volt secondary coil of the power transformer. You are ready now to connect the plates of the oscillator tubes to one end of the oscillation choke coil and bring a lead from the other end of this to one side of the blocking condenser; connect the other side of this with one of the posts of the filter reactor and the power transformer and connect the other end of the filament to the other end of the filament secondary coil. This done, connect one of the plates of the rectifier tubes to one end of the 550-volt secondary of the transformer which is the middle coil, and the other plate of the other rectifier tube to the other end of this coil. Connect the filter reactor and the filter condensers to the mid-taps of the filament secondaries and con- nect one end of the filter reactor to the mid-taps of the rectifier secondary. Now connect clip 3 of the tuning coil to one side of the blocking condenser and the other side of this to the oscillation choke coil and the latter to the mid-tap of the rectifier filament secondary; connect the movable switch contact of the primary of your power transformer to one of the 1 10-volt alternating current service wires and connect the other terminal of the primary with the other service wire. Your wireless telephone is ready now for a tryout. CHAPTER V HOW VACUUM TUBE TRANSMITTERS WORK Like the spark gap and the arc lamp the vacumn tube will set up oscillating currents. Unlike the spark gap but like the arc lamp the vacuum tube sets up sustained oscillations which, in turn, send out continuous waves and these can be used for either telegraphy or telephony. The Vacuum Tube as an Oscillator. — ^When the vacuum tube is used as an oscillator, that is, as a means for setting up oscil- lations, three coils must be used as in a regenerative receiving set, but instead of being loose coupled they must be close coupled, hence, the tuning coil is made of one continuous length of wire wound up into turns as shown at A in Fig. 186. The coil is divided into three parts by means of the adjustable clips. The top part of the coil acts as the tickler, the middle part as the primary and the lower part as the secondary. As in the re- generative receiving tuning coil the tickler feeds back a portion of the oscillations that are generated by the tube to the grid and as in the case of an amplifjdng tube (see Chapter III, Part IV), this augments, or amplifies, the voltage that is impressed upon it by the source of current which, let us suppose for the sake of sim- plicity, is a battery. There are any number of ways to hook up a vacuum tube oscillator with the other parts of the transmitter, but in the last analysis all of them, that is, if they are operative, amount to the same thing. Those I have given in the preceding chapter may be taken as typical of the best designed ones. To start the oscUla- 198 HOW VACUUM TUBE TRANSMITTERS WORK 199 tions going in the tube, all you need to do is to switch on the plate current; this will at the same time energize the grid when it aug- ments the oscillations that flow through the oscillation circuit which includes the middle or primary coil, the filament, plate and condenser (see Fig. 192). Connecting in a Vacuum Tube Oscillator.— To get the proper relation between that part of the tuning coil which is con- nected with the plate and that part which is con- nected with the grid you must adjust the first and second clips. It is neces- sary to maintain a balance between the values of the inductance coils and the condensers, for where the former are small and the latter are large the oscilla- tions that are set up may get very small or stop en- tirely. When this takes place it is necessary to increase the inductance of the coils or de- crease the capacitance of the condensers. By using the proper size coils and condensers the frequency can be made as high or as low as you want them within wide limits and, hence, you can send out waves of whatever length you want. The government regu- lation, however, fixes the maximum wave length for amateurs at 200 meters. About High Power Oscillator Tubes. — To set up oscillat- ing currents of high power two things are necessary and these are: (1) the tube must have a high vacuum, and (2) the plate must be energized by a high voltage. In the largest oscillator tubes that are made for amateur use to-day the plate is energized by a cur- rent of 2,000 volts and the plate current, that is the current that flows from the plate to the filament, is J of an ampere and this gives a normal output of 250 watts or about ^ of a horsepower. Fig. 192. — How the Oscillations Are Formed in the Oscillator Tore. 200 THE BOOK OF WIRELESS A tube to stand up under this voltage and current must have a high vacuum and the higher this is the more readily will it set up oscillations and the longer will it last. To carry a large current the tube itself must be large and means must be provided for radiating the heat. On the Use of Oscillator Tubes. — The temptation of most beginners is to force the oscillator tube to generate higher power oscillations than it was intended for; this they do by overloading it, that is, to increase the filament brightness and add to the vol- tage of the plate. Where more power is wanted a far safer and, in the end, a less expensive way is to connect two oscillation tubes in parallel and then cutting down the filament brilliancy a little. When you have your transmitting set all hooked up and are ready to try it out for the first time do not apply more than half of the rated voltage to the filament and plate, until you find that you have all of the parts connected up O. K.; then you can heat the filament to brilliancy and give the plate its full voltage. To get the best service out of an oscillator tube and make it last the longest possible time you should connect a voltmeter across the terminals of the filament. By keeping the voltage at exactly the same value all the time you can extend the life of the tube to a very considerable extent. CHAPTER IV USEFtJIi INFORMATION Government Rules and Regulations. — The time was, and not so very long ago, when a boy could own any kind of a wire- less set, use any length of wave he wanted to and send messages wherever he pleased and no one could say him nay. But things have changed in the last couple of years and while anyone can still receive wireless messages without having a license no one can send wireless messages without having first passed an examination and received a lieense from the Govern- ment. There are three grades of licenses issued to amateurs by the Government and these are: (1) restricted amateur stations, (2) general amateur stations, and (3) special amateur stations. If you are a beginner, a restricted amateur license is the kind you want and this means that you can use a wave length of not more than 200 meters and a transformer having an input of J a kilowatt. The general amateur license permits you to use a wave length up to 200 meters just as the restricted amateur license does, but you can use an input of 1 kilowatt and, hence, send farther. Fi- nally, the special amateur station license gives you the right to use wave lengths up to 375 meters and a transformer having an in- put of 1 kilowatt. In order to get this kind of a license you must have had at least two years' actual experience in wireless. To get a license covering any of the above grades, you must write to the U. S. Radio Inspector who lives in your district. The following is a list of the districts and the city in the district where the Radio Inspector has his office. When you want to get a license simply address your letter to the U. S. Radio Inspector, Boston, Mass., or whatever the city is in your district where he 201 202 THE BOOK OF WIRELESS is located, and he will send you the proper blank forms to fill out. No fee or charge of any kind is made for an operator's license. Cities Where Radio Districts Inspectors abb Located First District Boston, Mass. Second District New York, N. Y. Third District Baltimore, Md. Fourth District Norfolk, Va. Fifth District New Orleans, La. Sixth District San Francisco, Cal. Seventh District Seattle, Wash. Eighth District -Detroit, Mich. Ninth District Chicago, 111. Full information relating to all grades of licenses can be had by sending 15 oents to the Superintendent of the Government Printing Office, Washington, D. C, for a little book called Radio Communication Laws of the U. S., and another called Interna- tional Radio Telegraph Convention. Summary. — Boiled down, then, the government will permit you to (1) receive messages without a license, but (a) you must keep secret all messages you receive, and (2) send messages after you have obtained a license, providing that (a) your wave length does not exceed 200 meters, and that (b) the input of your transformer is not more than 1 kilowatt. Fees. — The government makes no charge for any operator or station license. Rules and Reqturements of the National Board of Fire Underwriters for Wireless Telegraph Apparatus. — The fol- lowing Paragraphs are taken from the National Electrical Code, a copy of which may be had for the asking by addressing the National Board of Fire Underwriters, 135 William Street, New York City: Section 86. Wireless Telegraph Apparatus. Note. — These USEFUL INFORMATION 203 rules do not apply to wireless telegraph apparatus installed on aiap;- board. In setting up wireless telegraph apparatus, all wiring within the building must conform to the general requirements of this Code for the class of work installed and the following additional specifi- cations : (a) Aerial conductors (wires) to be permanently and effectively grounded at all times when station is not in operation by a con- ductor not smaller than No. 4 Brown and Sharpe gauge copper wire, run in as direct line as possible to the water pipe at a point on the street side of all connections to said water pipe within the premises, or to some other equally satisfactory earth connection. (b) Aerial conductors (wires) when grounded as above specified must be effectually cut off from all apparatus within the building. (c) Or the aerial to (can) be permanently connected at all times to earth through a short-gap lightning arrester; said arrester to have a gap of not over .15 inch between brass or copper plates not less than 2i inches in length parallel to the gap and li inches the other way with a thickness of not less than J inch mounted on non-combustible, non-absorptive insulating material of such dimen- sions as to give ample strength. Other approved arresters of equally low resistance and substantial construction may be used. (d) In cases where the aerial is grounded as specified in para- graph (a) the switch employed to join the aerial to the ground con- nection shall not be smaller than a standard 100-ampere knife switch. (e) Where current is obtained direct from the street service the circuit must be installed in approved metal conduits or armored cable. In order to protect the supply system from high potential surges, there must be inserted in the circuit either a transformer having a ratio which will have a potential on the secondary leads not to exceed 550 volts, or two condensers in series across the line, the connection between the said condensers to be permanently and effectually grounded. These condensers should have a capacity of not less than one-half microfa/rad. List of Land and Ship Stations. — A list of land and ship stations of the United States, including amateurs, and giving caU letters, wave lengths, nature of service, etc., can be had by sending 15 cents to the Superintendent of Documents, Govern- ment Printing Office, Washington, D. C. APPENDICES APPENDIX A Brown and Sharpe Wire Gauge. — ^A wire gauge is not only used to find the sizes of wires, but to measure them as well. A wire gauge is a flat piece of steel cut in a circular form about ■Jg-inch thick and 2 J inches in diameter. It has 36 slots cut iu Fig. 193. — Beown and Shabpe Wikb Gaxtgb. its edge and each slot is stamped with a number beginning with 5 and ending with 36; and each number is the size of the wire which fits into its respective slot. The holes at the end of the slot have nothing to do with the size of the wire. A cut of the Brown and Sharpe gauge, which is also called the Standard 204 APPENDICES 205 Wire Oaaige, is shoim full size, so that you can roughly judge the number of any of the larger sized wires. Brown and Sharpe wire gauge is abbreviated B and S gauge; a B and S wire gauge costs about $2.10. APPENDIX B Drills. — Drills for drilling holes in wood and metal are used with a dxiU stock. The drills are called twist drills, and the sizes of drills needed for doing the work set down in this book are: No. of Drill For Taps or Screws 38 For , 4—36 32 For 6—32 28 For 8—32 22 For 10—24 13 For 12—24 The smaller drills cost about 5 or 6 cents each, and the larger drills cost about 10 or 12 cents each. APPENDIX C Taps and Dies. — Taps are for cutting inside threads, as in nuts, while dies are for cutting outside threads, as on screws. Taps are used in a wrench and dies are used in a stock. A set including the following sizes with wrench and stock iu a box costs $4.25. No. Threads to Inch 4 36 6 32 8 32 10 24 12 24 APPENDIX D Screws and Nuts.^-Machine screws and nuts nm in the same sizes as taps and dies. The size is found with a Brown 206 THE BOOK OF WIRELESS and Shaxpe standard screw gauge. Wlien you ask for a 4 — 36 screw or a 4 — 36 tap you mean that you want a screw or a tap size No. 4 Brown and Sharpe screw gauge and wMch has 36 threads to the inch. No. Threads to Inch 4 36 6 32 8 33 10 24 12 24 APPENDIX E Types of Aerials. — There are a number of types of aerials and the kind of an aerial you will put up will probably depend very largely on conditions. The very simplest type is the ver- tical aerial. The vertical aerial has very little capacity and is Fig. 194, — Vertical ATRIAL. Fia. 195. — Horizontal t (Inverted L) Aerial. now seldom used. The type described in Chapter III, Part II, is called a horizontal or flai-top, the first being called a T aerial for the reason that the leading-in wire is connected in the mid- dle of the aerial and this makes it look somewhat like the cap- ital letter T. The second form is the inverted L (l) aerial, the leading-in vrire in this case being connected with the aerial at one end or the other. The horizontal aerial of either form is a much better radiator of electric waves than the vertical aerial, and is widely used. The horizontal aerial is the type used at the great Arlington Station. Another type is the fan aerial^ of APPENDICES 207 which there are, likewise, two forms. In the first form the aerial is put up with all the wires insulated from the top of the pole Fig. 196. — Hokizontai, T Aerial. and spreading out and down toward the groimd. In the second form the wires are fastened to a wire or rope stretched between Via. 197. — Fan Aerial. two poles and are brought down to the ground in a single wire. A fan aerial is almost as good as a horizontal aerial, especially if FiQ. 198. — ^Umbrella Aehial. a large number of wires are used. The fan aerial is the type used at the great Eiffel Tower Station in Paris. A modification 208 THE BOOK OF WIRELESS of the fan aerial is to spread out the wires all around the pole when it becomes an umbrella aerial. This makes a better aerial than any of the other types. APPENDICES 209 DEFINITIONS OP SOME WORDS AND TEEMS USED IN THIS BOOK Abbreviations. The shortening of words or sentences for wireless messages. For in- stance, instead of spelling out the whole message, "How do you receive me?" you sim- ply send the letters Q R K, which also means "I am re- ceiving well." Act of Congress of Angnst 13, 1912. Laws passed by Con- gress to regular wireless com- munication. See Part III, Chapter III, page 196. Aets. Laws passed by Con- gress. Adjustable. (1) to Change by steps. (2) A word inter- changeably used with varied, as an adjustable resistance. Adjustable resistance. A resist- ance which can be changed so that exactly the amount of current needed will flow through the circuit. AeriaL See Appendix E. Aerial conductors. Aerial wires. Aerial rope. A rope fastened to the end of an aerial and brought down through a pul- ley block. Aerial wire system. An aerial and ground wire and that part of an inductance coil which connects them. Affected. To act upon or to be moved by. Alternate. To change in direc- tion. Amateur. One who practices wireless for the fun and in- terest and not for the money there is in it. Ampere. (1) The unit of cur- rent strength. (2) A fresh dry cell will develop from 15 to 26 amperes. Antenna. An aerial. Arc across. A continuous flame between the ends of the sec- ondary coil of a transformer. An arc differs from a spark, ■v^hich is a periodic luminous discharge. Ann. A projecting piece of metaL Back center. One of the two fixed points of a winding ma- chine or lathe between which a spool or form is held and turned. The back center is the left-hand center; it is also called a dead center. The right-hand center is called a live center. Ball and socket joint. A joint connecting the head band and ear-pieces of a telephone re- ceiver so that they can be turned in almost any posi- tion. Bell wire. No. 18 Brown and Sharpe gauge copper wire, double cotton-covered, paraf- fined and colored so that when a number of wires are run together they C£in be told from each other without sorting them over. Bookbinder's cloth. A kind of glazed cloth used for covering books, also for covering small induction coils. Broken. When a circuit is not completed it is said to be broken. 210 THE BOOK OF WIRELESS Call letters. Letters by which ship and shore stations are known. Three letters are used for all Navy, Army and Commercial stations. The eaU letters of the Government Station at Arlington, Va., are N A A. CaU signal. The figures and let- ters by which your station is known. The call signal of your station is given you by the Government when you re- ceive your license. Cell. (1) A single element for producing a current, as a dry cell. (2) Two or more cells coupled together form a bat- tery. Chalcopjrrite. Copper pyrites, a brass-colored mineral used as the sensitive element in crys- tal detectors. (See Zineite.) Closed. When a circuit is com- pleted, or made, by means of a key, interruptor, etc., the circuit is said to be closed. Cohere. To draw together. When electric oscillations surge through a loose contact such as is formed by a steel needle resting on a pair of leads, the molecules of the steel and lead are drawn to- gether, or cohere. Collar. A ring or band of metal. Composition foil. A low grade of tin foil made so by the ad- dition of lead to the tin. Conductive coupling. An aerial and a ground wire, forming an open circuit, and a closed circuit, which are connected together by a single induct- ance coil. Also termed a di- rect coupUng. Contact point. The spot where contact is made between two substances. The spot where a metal or a crystal touches an- other piece of metal or a crystal. Contact points. Any two wires or electrodes which are used to make and break a current, as the contact points of an interrupter or the contact points of a key. Continuous. Without a break. Contractile spring. A spiral spring which draws together, or contracts, when the tension is removed. Conventional symbols. A num- ber of different marks, fig- ures and signs which wireless workers have agreed to use to represent certain pieces of apparatus. Counter-sink. An enlargement of a hole for a screw so that the head of a screw will set in flush with the surface. Crystal detector. A detector in which crystals such as silicon, zineite, etc., are used as the sensitive element. Crystalline. Pertaining to or like crystal. Cut-in. To put more resist- ance, inductance or capacity in a circuit, as to cut-in a turn of wire. Cnt-out. To take some resist- ance, inductance or capacity out of a circuit, as to eut-oitt a Leyden jar. Cycle. (1) A series of changes which when completed are again at the starting point. (2) A period of time at the end of which an alternating or an oscillating current re- peats its original direction of flow. APPENDICES 211 Damped out. (1) The rate at which electric oscillations de- crease or die out. (2) Elec- tric oscillations are damped out by the resistance and the inductance of a circuit and the change of energy into electric waves. Determine. To fix or to make, as the inductance of a circuit determines its period of oscil- lation. Device. (1) An apparatus or instrument or part thereof. (2) Any arrangement for pro- ducing a required result. Die. A steel block with teeth on its inner surface. It is used for cutting threads on rods, etc. Direct coupling. An aerial and ground, forming an open cir- cuit, and a closed circuit, which are connected together by a single inductance coil. Also termed a conductive coupling. Disk. A thin, circular piece of metal or wood. A telephone diaphragm is a disk of sheet iron. The cheek of a coil is a disk of wood. A pie is a disk formed of wound-up wire. Eddy currents. Electric cur- rents set up in the core of a transformer by the currents flowing in the primary coil. These eddy currents waste the primary current by devel- oping heat in the core. The way to prevent eddy currents is to make the eoil of very thin strips of soft iron and then varnish the strips. Electric oscillations. The same ae high-frequency currents. Electric pressure. The force that moves a current along a wire. It is called electro- motive force. The unit of electromotive force is called a volt. Electric waves. Waves in the ether sent out by electric os- cillations in an aerial wire. Electrodes. Usually the parts of an apparatus which dip into a liquid and carry a cur- rent. The electrodes of a bat- tery are the zinc and carbon elements; the electrodes of an electrolytic interrupter are the copper rod, or platinum point and the lead plate; the electrodes of a spark-gap are the metal points or balls between which the sparks pass. Electrose insulator. Insulators for aerial wires made of a patented compound having a high resistance and great strength. Energy. The power of an elec- tric current. Ether. A substance filling all space and in, by and through which light, electricity and magnetism travels. Examination. Testing the skill and knowledge of an operator by a wireless inspector to as- certain if he should be granted a license. Eye. A hole in the ring of an insulator or a withe. Pactor. One or more causes that produce an effect, as the capacity of an aerial wire is a factor in determining its wave length. Feebly damped oscillations. High-frequency electric cur- rents which ^ing, or oscil- 212 THE BOOK OF WIRELESS late, a large number of times before they die out. Feed. To supply to; to furnish with. Finger. A small strip of metal. Fixed condenser. A condenser whose capacity cannot be changed. Flaming arc. The continuous luminous discharge which takes place between the ends of the secondary coil of a transformer. Flat-top aerial. See Appendix E. Flexible cord. A number of veiy thin copper wires twisted together and having a silk or cotton covering woven about them so that it will bend easily. It is used for connecting a detector with a telephone receiver. Fools' gold. Iron pyrites, a yel- low mineral which glitters like gold. It is used in crys- tal detectors for the sensi- tive element. Free end. All through this book you will find the term free end used. After a wire, or spring, or other piece of metal, is fastened at one end the other end is called the free end, at least until it is ^fastened to something else or something else is fastened to it. Full load. Using as much cur- rent as the apparatus is de- signed to use. Said of a trans- former when it is taking its full amount of current. Generator. (1) A dynamo. (2) Any machine or apparatus which produces a current of electricity. Government rules and regula- tions. See Part III, Chapter III, page 196. Ground clamp. A clamp for making a good connection be- tween the ground wire and a pipe. Guy out. To fasten a pole or mast in position with ropes, called guy ropes. Hack saw. A small saw used for sawing metals. Hard fiber. An insulating ms/- terial made of the pulp of pa- per which has been toughened and waterproofed by chemi- cals aaid hardened by pres- sure. Hard solder. An alloy used by jewelers for soldering gold, silver and other metals; it only melts at red heat. It is melted by means of a blow- pipe. Head telephone receiver. One or two watch-case receivers joined together with a metal or hard rubber band which fits over the head and holds the receivers closely to the ears. HeUx. (1) A tuning coil for, sending. (2) A spiral of wire. High-frequency currents. The same as electric oscillations. High potential surges. Currents of high pressure which some- times back up into the pri- mary of the transformer and into the feed wires. Such surging currents will bum out the generator and do other damage unless devices are in- stalled to prevent them. High-power station. Stations using large amounts of APPENDICES 213 power. The Government sta- tion at Arlington, Va., has a sending range of about 3,000 miles. High-pressnre circuit. The cir- cuit of the secondary coil of an induction coil, or of a transformer. The pressure in these circuits may range from 5,000 to 300,000 volts. High-pressnre current. A cur- rent such as is usually pro- duced by the secondary coil of an induction coil or a transformer or the discharge of a Leyden jar or glass plate condenser. A high-voltage current. High-pressnre electricity. Same as high-pressure current. A current such as is usually produced by the secondary of an induction coil or a trans- former or a Leyden jar. Horizontal aerial. See Appen- dix E. Horse-power. One horse-power equals 33,000 pounds, raised 1 foot in 1 minute. Incoming waves. Electric waves which impinge or strike the aerial of a station. Jump sparks. Electric dis- charges produced by an in- duction coil or a condenser. Lead. (1) To carry a wire to. (2) A wire carrying a car- rent. Lever. A bar of metal which moves freely on a fixed point. License. Permission given by the Government to a person to operate a wireless sta- tion. Licensed operator. A wireless operator who is licensed to operate a station. Lines of Magnetic Force. Curved lines of force extending from one pole of a magnet to the other. If a magnet is placed under a sheet of glass or a heavy sheet of paper and fine soft iron filings are sprinkled over the glass or paper the filings will move about and form themselves into curved lines which show the lines of magnetic force. Linking. Joiaing together. List of land and shore stations. Published by the U. S. Gov- ernment. A list of wireless telegraph stations of the U. S. The edition of 1915 gives the names of all the ship and shore stations, their call sig- nals and the wave lengths which they use. It also gives the names of all the boys and amateurs who own licensed stations, the location of their stations, their call signals and the power in watts which they use. Send 15 cents to the Superintendent of Docu- ments, Washington, D. C, and he will send you a copy. Idstening-in. Listening to wire- less messages. Loose contact. Contact between conductors without pressure. When a steel needle is laid across the leads of a detector a loose contact is formed which is sensitive to electric oscillations. Low-pressure circuit. The cir- cuits of the generator and primary coil of an induction coil or a transformer. The pressure in these circuits may range from 110 to 220 volts. iU THE BOOK OF WIRELESS Low resistance, resistance. Having little Made. When a circuit is com- pleted by means of a key, in- terrupter, contact of wires, or spark-gap the circuit is said to be made. Magnetic force. The magnetiz- ing power of a current in the magnet coils. Mains. The wires which carry the current from the street service into the house. Masthead. The top or highest point of a wireless pole or mast. Meter. A meter is 39.39 inches long. Mica. A transparent mineral, sometimes called isinglass, which can be split into very thin sheets. It is a very good insulator and is largely used in making condensers. Microfarad. The ttiW of a farad. National Board of Fire Under- writers. A Board organized to enforce such rules and reg- ulations as the Electrical Committee of the National Fire Protective Association may recommend. See Book III, Chapter III, page 199. National Electrical code. The rules and requirements laid down by the National Board of Fire Underwriters. Nantical mile. A nautical, or sea, mile is 6,087 feet. A statute, that is a legal, or or- dinary mile in the United States, is 5,280 feet. Non-absorptive. A substance which will not absorb water. Non-combustible. A substance which will not bum. Ohm. The imit of resistance. The resistance of 400 feet of common telegraph wire is about one ohm. Open. When a circuit is not completed or is broken, it is said to be open. Open key. When a circuit is broken by means of a key, the key is said to be open. Oppose. To offer resistance. Oscillating currents. Currents which surge with high fre- quency in open or closed cir- cuits. Oscillation. (1) The swing of a pendulum. (2) The swing of a high-frequency current. (3) A train of electric oscilla- tions set up by a single spark. Out-going waves. Electric waves which ^"e emitted or sent out by the aerial of a station. Parallel. When all the zincs of a battery are connected to- gether and all of the carbons are connected together, the battery is said to be con- nected in parallel. Period. The length of time it takes a pendulum or an elec- tric oscillation to make a complete swing. Power switch. A switch placed in the circuit formed by the generator and the primary of the transformer. Principles. The first causes that produce results. Process. The way of working, the course of procedure. Qnick break. A quick separa- tion of the contact points of APPENDICES £15 an interruptor. A qtiiek sep- aration of an electric circuit. A quick break and the num- ber of breaks per minute which an interruptor makes are entirely different things, but both are needed for the proper working of an induc- tion eoil. Badiated. Sent out, as electric waves are radiated from an aerial wire. Radio. Wireless. The word raddo was adopted by the In- ternational Radio Telegraphic Convention to take the place of the word wireless. Wire- less and radio mean exactly the same thing. Badio Communication Laws of the United States. See Part ni, Chapter III, page 196. Beam. To enlarge a hole. Beamer. A tool for enlarging holes. Rectified. To change an oscil- lating current into a direct current. Oscillating currents are reeUfied or changed into direct currents by crystal de- tectors. Resistance. The friction offered by a wire or other conductor to the passage of a current. Respond. To act when a force is applied, as a detector re- sponds to the action of elec- tric oscillations. Beversal. Change of the direc- tion of the flow of a current. Bevolving element. The spool, or form, including the spindle on which it is fixed in a wind- ing machine. Roughly tuned. To be tuned nearly enough for practical purposes. Satisfy. To fulfill aU the re- quired conditions. Scale. Spaces or divisions marked off for the purpose of measurement, or comparison, as the scale of a hot-wire am- meter. Sending helix. A tuning eoil for sending. Sensitive. Affected by a very small current. A detector is sensitive when it will respond to oscillations of one sTiW of an erg. Series. When the zinc of one cell is connected to the car- bon of another cell the bat-" tery thus formed is said to be connected in series. Shank. (1) The part of a bolt between the threaded end and the head. (2) The part of a leading-in insulator next to the shoulder. Shoulder. (1) The bulging part of a leading-in insulator which sets up against the window pane. (2) An offset for keeping a thing in place. Silicon. A chemical element used in crystal detectors for the sensitive element. It is one of the most sensitive of the rectifying crystals. Slider. A piece of metal which slides along rods or other guides and which carries a contact spring. Slot. A slit or narrow cut in a piece of metal, as a slot in a screw head. Soft-drawn wire. Wire which is not made springy dur- ing the process of making. This kind of wire is easily handled when making aerials. 216 THE BOOK OF WIRELESS Source of cnrrent. A battery or any kind of a generator of electric currents. Specifications. The definite statement of requirements of the National Board of Fire Underwriters for installing wireless stations. These are included in the National Elec- trical code. Static. Atmospheric electricity which charges the aerial and discharges through the de- tector. When the static is strong close your lightning switch. Stem. A slender cylindrical piece of metal. Stepptag-iip. Increasing the pressure of a current, as an induction coil, or a trans- former steps-up the pressure of a current. Stranded wire. Aerial wire made up of a number of small wires twisted together. Strongly damped oscilUtions. High-frequency electric cur- rents which make only a few swings, or oscillations before they die out. Snccession. Following each other at regular intervals. Support. A piece of wood or metal which holds something in place. Surging. Moving to and fro; oscillating. Said of high-fre- quency currents in a cir- cuit. T aerial. See Appendix E. Tap. A tool for cutting inside threads. Taper. Smaller at one end than at the other. Taut. To stretch tight, as a taut aerial. Telephone cord. See Flexible cord. Thread. (1) The tooth of a screw. (2) To cut threads on a rod with a die. (3) To thread a nut. Thumb screw. A screw or nut having wings on it so that it can be tightened or loosened with the thumb and fingers. Trains of waves. Electric waves which follow each other at regular intervals. Each elec- tric oscillation sends out an electric wave and, hence, as several oscillations take place before all the energy is damped out, an equal number of electric waves will be sent out. This forms a train of waves. Transferred. The energy of a current flowing in a primary circuit or coil which is changed over to current which is set up in the secondary coil or circuit. This transfer of energy takes place by induc- tion. Tone in. To tune a receptor so that the signals from the sta- tion wanted are the loudest. Tune out. To tune a receptor so that the signals of all sta- tions not wanted are weakest. Tuned dosed circuit. (1) A cir- cuit formed of a condenser, inductance coil and a spark- gap for a transmitter. (2) A circuit formed of a con- denser, inductance coil and a detector for a receptor. Tuned open circuit. A tuned aerial wire system. Variable. To change gradually, as a variable condenser. Variable condenser. A con- APPENDICES 217 denser whose capacity can be changed. Variable resistance. A device for regulating a current flow- ing in a circuit, as a water resistance in the primary cir- cuit, or a potentiometer in the receiving circuit. Vibrate. To move to and fro rapidly, as the diaphragm of a telephone receiver; to swing; to oscillate. Volt. The unit of electric pres- sure, or electromotive force as it is called. A dry cell will develop from IJ to 2 volts. Washer. A small flat metal ring placed on a screw be- tween the head or below a nut to serve as a cushion. Where a connection is to be made with a screw two washers are slipped on the screw, and the wire is looped around the screw between them. Watt. (1) The unit of work done by a current. (2) One ampere X one volt := one watt. (3) 746 watts = one horse-power. (4) a dry cell giving 20 amperes at IJ volts will develop 24f of a horse- power. Wire np. (1) To connect all the parts of an apparatus with wire. (2) To completa all necessary circuits. Wireless code. (1) The Inter- national Morse code. (2) The alphabet arranged in dots and dashes. (3) A modifica- tion of the regular Morse code. Wireless eye. A fanciful name given to detectors, since de- tectors sense electric waves which are too long for the eye to see through the electric os- cillations which are set up. Wireless key. A device for making and breaking up a current into dots and dashes. A key for wireless work usu- ally has larger contacts than an ordinary telegraph key. Wireless waves. (1) Electric waves. (2) The waves sent out through space by oscil- lating currents in an aerial wire. Work. To energize, to operate, as to work a transformer. Zincite. A deep red mineral crystal. It is used in crystal detectors as a sensitive ele- ment. Zincite is very sensi- tive to electric oscillations when in contact with chalco- pyrite. INDEX A battery, 160, 167. Abbreviations, in code, 40. About high power oscillator tubes, 199. Action of a tuned receptor, 147. of a tuned transmitter, 145. Adjustable condenser, 167. Aerial, assembling the, 117. ball insulators for, 116. brass stops for, 117. bridle for, 26. connecting with transmitter, re- ceptor and groimd, 131. cost of materials for cheap, 33. electric current in, 47, SO. fan, inverted L, T, umbrella, vertical, 206. high-frequency currents in, 101. horizontal or flat-top, 113, 206. leading-in, middle, and end spreaders for, 115. leading-in wire for, 26, 115. making an, 113. spreader withes for, 115. spreaders for, 24. waves around, 49. Aerial ammeter, 187. Aerial condenser, 187. Aerial insulators, 24r-25. Aerial rojje, 24, 26. Aerial series condenser, 189. Aerial switch, base and support for, 125. complete, 128. contact lever for, 126. cost of, 33, 124. for small set, 28. Aerial wire, 23. kinds of, 24. leading-in insulator for, 120. Aerial wire system, a good, 112. Aerials, kinds of, 206. S hooks for, 116. steel wire for, 116. thimbles, tackle blocks, shackle bolts, and manilla rope for, 117. Alternating current, connecting up transmitter for, 73, 145. description of, 58. frequency of, 146, 147. high-pressure, 57. Alternating current transformer, 189, 192, 193. Alternating current voltmeter, 187. Aluminum wire, 24, 114. Amateur, boy, 156. Amateur Ucenses, 201. Ammeter, hot-wire, 148, 149, 187. Ampere, 56. Amplifier, how the vacuum tube works aa an, 179. one step, 169. two step, 169. vacuum tube, 155, 167, 168. Amplifier receptor, audio frequency, 157. crystal detector, 169. one step vacuima tube, 162. radio frequency, 157. resistance coupled, 169. two stage, 157. Amplifier tube filaments connected in parallel, 171. Amphfiers in cascade, 170. Amplifying audio frequency oscil- lations, 179. Amplifying receptor with vacuum tube detector, 169. Amplifying receptor works, how the Armstrong, 180. Analogue, of rubber ball, 47. Anchor-gap, 123. Appendices, 209. Arc, oscillation Collins, 156. Arc system, electric, 155. Arkay loud speaker, 172. Arlington, Government station at, 81. Armature, for coil-spark, 7. Armstrong circuit, 155. Armstrong regenerative feed-back, 164. Armstrong regenerative receptor, a simple, 163. how it works, 180. Audio frequency amplifier recepttw, 157. 219 g£0 INDEX Audio frequency, defined, 178. Audio frequency oscillations, am- plifying, 179. Audio frequency transformer, 170, 171. Auditory nerve of ear, 53. Ball insulators, 116. Base, for strap key, 4. Battery, A, 160, 167. B, 160, 167. dry ceU, 2, 162. microphone, 195. of Leyden jars, 59. powerof, 58. storage, 160. B battery, the, 160, 162, 167. Beat C. W. telegraphy receptor, 173. Beats explained, 180. BeU wire, 3. Binding post, dry cell, 3. Binding post, for key and spark- coU, 5. triple, 106. with wood screw, 85. Blocking condensers, 195. Boy amateur, 156. Boys, wireless, 156. Brass stops, for aerial, 117. Bridle, for aerial, 26. Broadcasting, first, 156. receptors, 157. Brown and Sharpe wire gauge, 204. Buzzer, the use of the, 178. By-pass condenser, 187, 189. Capacitance, 164. Capacity, electrical, 140. of a gallon bucket, 140. of Leyden jars, 62. Cascade amplification, 170. Choke coil, 184, 187, 189, 192. Chopper, 186. coimecting in the grid, 191. how it is connected in, 190. the use of the, 178. Circuit, diagram of alternating cur- rent, 59. diagram of tuned closed ocsilla- tion, 142. Circuits, clqsed oscillation, 142, 143. coupled oscillation, 143-145. open oscillations, 141, 142. tuned open, 133. Clip, spring, 73. Code, abbreviation of, 40. Continental Morse, 37. dot and dash, 35. first aid to remembering the, 38. how to learn the, 37. International Morse, 36. Morse, 35. spacing of, 39. Coil, induction, 6. spark, 6. Collins arc telephone, 156. Communication laws, radio, 202, Condenser, adjustable, 167. aerial, 187, 189. by-pass, 187, 189. charge and discharge of a, 146. complete, 97. filter, 182. and blocking, 195. fixed, 162, 167. for receptor, 82, 95. grid, 187, 189. laying up, 96. of Leyden jars, 58, 65. of wave meter, 152. rotary, 151. soldering wires to, 97. variable, 162. Coimecting amplifier tube filaments in parallel, 171. Connecting in a vacuum tube os- cillator, 199. Connecting up vacuum tube fila- ments, 170. Contacts, for key, 60. Continental Morse code, 37. Continuous wave telephony, 155. Continuous wave wireless, 155. Continuous waves, 158, 173, 182. Convention international radio tele- graph, 202. Conventional signals, 41. Conventional sjTnbols, 54. Cords, for telephone receivers, 100. Core, for spark-coil, 6, 44. of transformer, 59. Cost, of baby-knife switch. 111. of crystal detector for receptor, 111. of ground, 33. INDEX 221 of hot-wire ammeter when home- made and when bought, 154. of making key, Leyden jar con- denser, spark-gap, and tun- ing coil, 79. of materials, for cheap aerial, 33. to make small sender, 11. of 1,000 ohm telephone receiver, 111. of potentiometer for receptor, 111. of receiver when bought and when home-made, 22. of receptor when home-made, 111. of rotary condenser, 154. of small sender when bought, 10. of telephone receivers, 100. of transformer when home-made, 78. of transmitter when bought, 78. of tuning coU for receptor. 111. of water resistance when home- made, 78. of wave meter, 154. Coupled oscillation circuits, 143. Coupling, 164. Crystal detector, amplifier receptor, 169. cost of. 111. parts of, 92-94. simple, 81. Crystal detector receptor, 157. Crystals, for detectors, 101. Current, generation of alternating, 58. pressure of, 46. regulating flow of, 57. source of, 58. things to know about a, 66. Currents, altematiag, 45. cycles of alternating, 59. hagh-frequency, 46. C. W. telegraph receptor beat, 173. heterovogue, 173. C. W. telegraph transmitter dem- onstration, 184. five-watt, 186. Damped vibrations of spring, 158. Damped waves, 155. Definitions, of terms used, 209, 216, 217. Demonstration, C. W. telegraph transmitter, 184. wireless telephone transmitter, 186. Detector, cork, a water wave, 50. crystal, 90. crystals for, 101. development of vacuum tube, 159. howavacuum tube works as a, 177. of small receiver, 12. simple crystal, 16-18. vacuum tube, 158, 167. Development of vacuum tube de- tector, 159. Diagrams, how to read, 54r-56. Diaphragm, of telephone receiver, 18, 51. vibrations of, 52. Dies and taps, sizes of, 202. Direct current, connecting up ap- paratus for, 75, 101. intermittent, 147. Discontinuous waves, 155, 158. Distress signals, 41. Dot and dash code, 35. Double-pole knife-switch, 121. Drills, sizes of twist, 205. Dry ceU, 2, 14, 82, 104. Dry cell battery, 162. Duo-lateral coils, 172. Ear, human, 52. Ear drum, 52. as a sender, 53. Edison effect, 160. Eiffel Tower station, 157. Electric arc system, 155. Electric current, alternating, 45. direct, 43. in aerial, 47, 50. Electric currents, changed into sound waves, 50. pressure of, 45. Electi-ic oscillations, 139. Electric spark, 158. Electric spark system, 155. Electric wave meter, 150-154. Electric waves, 12. sent out by aerial, 50. Electrical tuning, 137-139. Electrode ball insulators, 116. Electrodes, for potentiometer, 104. spark, 70. Electrolytic interrupter, 77. Electromagnet, for telephone re- ceiver, 18. 222 ilSfDEX Electromagnetic induction, 146. Electromagnetism, 44, 45. Electrons defined, 175. Enamelled wire, 85. Ether, 49. Fan aerial, 206. Feebly damped oscillations, 143. Feed back, Armstrong regenerative, 164. Feed back circuit, 155. Fifty watt C. W. telegraph trans- mitter, 191. Fifty watt oscillator tube, 192. Filament brilUancy, 160. Filaments connecting up vacuum tube, 170. Filter condensers, 195. Filter reactor, 194. Filters, 182. Fire Underwriters, Rules of Board of, 73. Fire Underwriters' rules, 202. Five watt C. W. telegraph trans- mitter, 186. Five watt oscillator tube, 186. Five watt telegraph transmitter, connecting up the, 191. Five watt wireless telephone trans- mitter, 193. Fixed condensers, 162, 167, Flaming arc, 65, 124. Flat-top aerial, 113. Fleming's discovery, 160. Force, stored up in rubber ball, 47. Friction, of water, 57, 139. Galvanized iron wire, 24, 114. General amateur hcenses, 201. Generation, of alternating current, 58. Generators for high voltage plate currents, 183. Government licenses, 201. Government station, at Arlington, 81. Graphite potentiometer, 165. Grid chopper, connecting up the, 191. Grid condenser, 187, 189. Grid leak, 163, 167, 187. transmitting, 189. with mid tap, 184. Ground, a good, 128. connecting with aerial trans- mitter, and rec^tor, 131. cost of, 33. how to make a, 31. putting down a, 130. Ground connection, 30, 31. Grounds, 30. Head band, adjustable, for tele- phones, 100. Head-phones, 162, 167. Head telephone receivers, 101. Hear, how we, 53. Helix, for sending, 71. Heterodyne C. W. telegraph re- ceptor, 173. Heterodyne receptor, 186. how it works, 180. High-frequency currents, 46, 179. in aerials, 57, 81. in receiving aerial, 101. High power oscillator tubes, 199. Honey-comb coils, 163, 164, 172. Honolulu government station, 157. Horizontal aerial, 63, 206. Horse-power, 57. Hot-wire ammeter, 148, 187, 190. complete, 149. how to use a, 149. How a three electrode vacuum tube works, 176. How a vacuum tube works as a de- tector, 177. How the Jumstrong regenerative receptor works, 180. How the chopper is connected in, 190. How the heterodyne receptor works, 180. How the vacuum tube works as an amplifier, 179. How to connect up, an A. C. wire- less telephone transmitter, 195. demonstration C. W. telegraph transmitter, 184. the 5-watt telegraph transmitter, 191. How to treat vacuum tubes, 178. How vacuum tube receptors work, 175. How vacuum tube transmitters work, 198. Human ear, 52. INDEX 223 Indian wireless signals, 34. Inductance, 140, 141. Inductance coil, of wave meter, 153-153. tuning, 189. Induction coil, 6. Inertia, 141. Inspector, U. S. radio, 201. Insulated copper wire, 7. Insulated staples, 71. Insulator, leading-in, 27, 120. Insulators, aerial, 24, 25. porcelain, 25. Intermediate wave receptors, 170. International Morse code, 36. International Radio Telegraph Con- vention, The, 202. International Radiotelegraph Con- vention, in London, 37-39. Interrupter, 6. adjusting the, 10, 57. electrolytic, 77. of spark-coil, 7. Inverted L aerial, 206. Isinglass, 95. Jump sparks, 6. Key, contacts for, 60. cost to make, 79. how to make a large, 60. large telegraph, 58. lever for, 62. strap, 3, 4. supports for, 60. telegraph, 2. what takes place when it is closed, 42. Knife switch, 121. Laws, radio communication, 202. Lajring up, a condenser, 96. Layout, of instruments on table, 75. of receptor apparatus, 105. of transmitter and receptor on table, 132. Leading-in insulator, 27, 120. Leading-in s^jreader, 116. Leading-in wire, for good aerial, 24, 26, 115. Leg, of transformer core, 59. Lever, for key, 62. Leyden jar condenser, 58. cost to make, 79. how to make, 65, 66. Leyden jars, battery of, 69. capacity of, 62. tuned, 138. License, United States Govern- ment, 57. Licenses, amateur, 201. Lightning switch, 121. Listening-in, 54, 133. London, meeting of International Radiograph Convention at, 37-39. Long distance telephone receiver, 100. Long wave receptors, 170. heterodyne, 174. Loose coupled tuner, 162, 167. Loud speaker, 156, 157. Arkay, 172. Magnavox, 172. Magnavox loud speaker, 172. Magnetic modulator, 193. Magnetism, 44. Mains, current taken from electric light, 58. Manilla rope, for aerials, 117. Mechanical tuning, 136. Message, how heard, 62. Mica, 95. Microphone, 182, 195. Microphone battery, 195. Microphone modulator, 195. Micrmjhone transmitter, 187. Modulator, microphone, 195. Morse code. Continental, 37. International, 36. learning the, 34. Motor-generator, 193. Negative electricity, 175. New wireless, 155. Non-tuned open oscillation circuit, 141. Nuts, sizes of, 205. Ohms, 57. On the use of oscillator tubes, 200. Open oscillation circuits, 141. Operation, of sending and receiv- ing apparatus, 133. Oscillating current, rectified, 147, 148. Oscillating currents, rectified, 160. Oscillation arc, 156. 224 INDEX Oscillations amplifying audio fre- quency, 179. a spark discharge, 159. electric, 139. feebly damped, 143. strongly damped, 142. sustained, 168. Oscillator, connecting in a vacuum tube, 199. vacuum tube, 182, 198. Oscillator tube, 5-watt, 186. 50-watt, 192. high power, 199. use of, 200. Periodic waves, 158. Phosphor-bronze springs, 86. wire, 114. Plate battery, 162. Plate currents, generators for, 183. Porcelain insulators, 25. Potentiometer, 100, 101, 166, 167. electrodes for, 104. Power permitted, 201. Power transformer, 187, 189, 192, 193 Power tube, 183. high, 199. Pressure, of current, 46, 56. of electric currente, 45. of steam, 56. of water, 45. Primary coil, of transformer, 7. Quality of electricity, 56. Radio communication laws, 202. Radio districts, 202. Radio frequency, 168. Radio frequency amplifier receptor, 157. Radio frequency currents, 179. Radio inspector, U. 8., 201. Radio Telegraph Convention, The International, 202. Reactor, filter, 194. Receiver, adjusting the small, 21. connecting up the small, 20. cost of small, 22. detector for, 12. dry cell for, 14. small, 12. Receiver switch, 12, 14, 15. Receiving condensers, 162. Receiving set, simple vacuum tube, 162. Receptor, wireless, 54, 81. action of a tuned, 147. adjustable resistance for, 82. adjusting the, 108. with potentiometer, 110. without potentiometer, 108. audio frequency amplifier, 157. beat C. W. telegraph, 173. condenser for, 82. connecting up, 105. with transmitter, aerial and ground, 121. cost of, 1,000 ohm telephone re- ceiver for, 111. potentiometer for. 111. tuning coil for. 111. when home-made. 111. crystal detector amplifier, 169. crystal detector for, 81, 157. heterodyne C. W., 173. loud speaker, 157. one-step amplifier, 168. radio frequency ampUfier, 157. regenerative vacuum tube, 157. resistance coupled, 169. simple Armstrong regenerative, 163. telephone receiver for, 82. tunmg coil for, 81, 82. two-stage amplifier, 157. vacuum tube, 157. vacuum tube detector, amplify- ing, 169. variometer regenerative, 166. wiring diagram of transmitter and, 134. wiring diagram for a simple re- generative, 163. wiring up, 106. Receptor works, how the hetero- dyne^ 180. Receptors, mtermediate wave, 170. long wave, 170. tuning, 136. vacuum tube, 158. how it works, 175. Rectified A. C. currents, 182. Rectified currents, 168. Rectified oscillating current, 149, 160. Rectifier vacuum tube, 193, 194. Rectifier valves, 194. INDEX 225 Regenerative circuit, 155. Regenerative feed back, Armstrong, 164. Regenerative receptor, simple Arm- strong, 163. wiring diagram for a simple, 163. Regenerative receptor works, how the Armstrong, 180. Regenerative set with variometer, 166. Regenerative vacuum tube receptor, 157. Resistance, adjustable, for receptor, 82, 139. of wire, 67. regulating, 59, 146. variable, 62. water, 62. Resistance coils, 182. Resistance coupled amplifier re- ceptor, 169. Resistance coupled receptor, 169. Restricted amateur licenses, 201. Reversal of current, 59. Rheostat, filament, 162, 167. Rope, for aerial, 24, 26. Rotary condenser, 151. Rotating oscillation arc, 156. Rubber-covered copper wire, 103. Rules of Board of Fire Under- writers, 202. Saturation defined, 176. S hooks, 166. Screws, sizes of, 205. Secondary coil of transformer, 59. Secrecy, selective, 156. Selective secrecy, 156. Sender, simple, 2. adjusting, 10. connecting up, 9. cost of materials to make, 11. cost of small, 10. Sending range, 57. Sending speed, 39. Sending tuning coil, 58, 71. complete, 74. Set, small wireless, complete, 32. connecting up, 31. Shackle bolts, for aerial, 117. Shellac varnish, 14. Signals, conventional, 41. distress, 41. Indian wireless, 34. of transmission, 39. SOS, 42. SiUcon bronze wire, 114. Single coil tuner, 162. Single pole, single throw switch, 31. Slider, for timing coil, 85. Sonometer, the, 180. Source of current, 58. South Sea Islander, kindling a fire, 139. Spark-coil, 6. primary tor, 7. secondary for, 7. spring for, 7. Spark discharge, oscillations of, 159. Spark, electric, 46. kinds of, 8. what a, does, 46. Spark electrodes, 70. Spark-gap, brass ball, 8. cost to make, 79. for small set, 7. large, 58, 66. zinc rod, 8. Spark systiem, electric, 155. Speed of electricity, 141. Spider web tuning coils, 163, 164. Splicing wires, 118. Spreader, end, 115. for good aerial, 115. leading-in, 115. middle, 115. Spreader withes, 115. Spreaders, aerial, 24. Spring, damped vibrations of, 158. Spring clips, 73. Standard wire gauge, 204. Static electricity, 31. Steel wire for aerials, 116. Stepping up pressure, 57. Storage battery, 160. Stranded wire, 114. Strap key, 3, 4. Supports for key, 60. Sustained osciUations, 158. Switch, connecting the aerial, with sender and receiver, 31. lightning, 121. receiver, 12, 14, 15. single pole, single throw, 31, 82, 105. small set aerial, 28, 134. Symbols, 54. used in wireless, 55. 226 INDEX T aerial, 113, 206. Tackle blocte, for aerial, 117. Tape and dies, sizes of, 205. Telegraph key, 187. large, 2. Telegraph transmitter, demonstra- tion C. W., 184. 6-watt, C. W., 186. Telegraphy, continuous wave, 155. Telephone receiver, 12. cords for, 18, 19. cost of, 180. diaphragm of,, 18. electromagnet for, 18. long distance work, 100. magnet of, 50. parts of, 19. receptor of, 82. watch-case, 50. Telephone receivers, 162. head, 98. Telephone transmitter, 182. demonstration wireless, 186. 5-watt wireless, 193. Telephony, continuous wave, 155. Thermionic valve, 160. [See also vacuum tube.] Thimbles, of aerials, 117. Three electrode vacuum tube works, how a, 176. Tickler coil, 164^180. Tin foil, 95. Transformer, alternating current of, 69, 189, 192, 193. audio frequency, 170, 171. power, 187, 189, 192, 193. primary of, 59, 146. secondary of, 59. size of, 59. Transformer cores, 59. Transmitter, adjusting, 77. complete, 76. connecting up, for alternating cur- rent, 73. for direct currents, 75. connecting with receptor, aerial and ground, 131. cost when home-made and when bought, 78. demonstration C. W. telegraph, 184. Transmitters, tuning, 136. vacuum tube, 182. how it works, 198. Transmitting grid leak, 189. Transmitting tuning coil, demo«- stration C. W., 185. Tuned closed oscillation circuit, 142. Tuned Leyden jars, 138. Tuned open circuits, 133. Tuned pendulums, 137. Tuner, loose coupled, 162, 167. single coil, 162. tickler cou, 164. Tuning, electrical, 137. mechanical, 136. Tuning coil, complete, for sending, 74. cost to make, 79. for receptor, 81-82. Tuning curls, honeycomb, 164. how to make, for receptor, 82. sending, 58, 71. sUdes for, 85. spider web, 163, 164. variometer, 166. Tuning inductance coil, 189. 3-cUp, 187. Twist drills, sizes of, 205. Umbrella aerial, 207. Unit, of pressure, 56. of quantity, 56. of resistance, 57. of work, 56. U. S. radio inspector, 201. Vacuum tube, as an amplifier, 155. as an oscillator, 198. how it works, as an amplifier, 179. as a detector, 177. how to treat, 178. rectifier, 193, 194. three electrode, 155. how it works, 176. two electrode, 155. Vacuum tube amplifier, 167, 168, Vacuum tube amplifier receptor, one step, 168. Vacuum tube detector, 158, 167. development of, 159. three electrode, 162. Vacuum tube detector amplifying receptor, 169. Vacuum tube filaments, connecting up, 170. Vacuum tube oscillator, 182. INDEX 227 connecting in a, 199. Vacuum tube receiving sets, 168. simple, 162. Vacuum tube receptor, 157. connections for a simple, 161. how it works, 175. Vacuum tube transmitters, 182. how they work, 198. Variable condenser, 162. Variable resistance, 101. Variometer, 165. regenerative receptor, 166. Vertical aerial, 206. Vibration of diaphragm, 52. Volt, 56. Voltmeter, A. C, 187, 190. Watch-case receivers, 100. Water, analogueof direct current, 43. Water, waves of, 48. Water resistance, 77. adjusting, 62. cost when home-made, 78. Watt defined, 192. Watts, 56. to find, 56. Wave length, permitted, 54, 201. Wave meter, complete, 153. construction and use of, 160. Waves, aerial, 49. continuous, 158. discontinuous, 165, 158. water, 48. wireless, 48-49. Wire, aerial, 23, 24. aluminum, 24, 123. beU, 3. enamelled, 86. galvanized iron, 24. insulated, 7. leading-in, 24. phosphor-bronze, 114. rubber-covered, 103, 114. silicon bronze, 114. stranded, 114. Wire gauge, kinds of, 204. Wireless boys, 166. Wireless, how, works, 42. new, 165. Wireless code, 36. Wireless station at Honolulu, 157. Eiffel Tower, 157. Wireless sjonbols, 55. Wireless telephone, 186. 5-watt, C. W. telegraph, 186. 5-watt wireless telephone, 193. how operated, 67. long distance, 57. wireless, 54. wiring diagram of receptor and, 134. Wireless telephone transmitter, an A. C, 196. wiring diagram of an, 196. demonstration, 126. wiring diagram of the, 187. 5-watt, 193. Wireless transmitter, 54. Wireless waves, 48. how made, 48-49. incoming, 51. Wires, splicing and joining, 118. Wiring diagram, a 5 or 50 watt C. W. telegraph transmitter, 190. for connecting up transmitter, 75. for small receiver, 20. heterodyne receptor, 174. Magnavox loud speaker, 173. of transmitter and receptor, 134. Wiring diagram, resistance coupled receptor, 169. Wood screw binding post, 4. (M) By A. FREDERICK COLLINS BOOK OF WIRELESS TELEGRAPH & TELEPHONE The most satisfactory book for the amateur. 200 illustrations. THE BOOK OF STARS Tells how, with a pair of good eyes, you can use the sun, moon and stars to suit your own purpose. THE BOOK OF MAGIC Clear directions on how to perform the simple as well as more difficult tricks of the great magicians. lUus. THE BOOK OF ELECTRiaTY A handbook of hundreds of electrical experiments for amateurs. Illus. GAS, GASOLINE AND OIL ENGINES A popular discussion of what sort of engine to buy, how to use and repair it. Illus. THE AMATEUR CHEMIST A clear and simple explanation of the truths of chem- istry. Illus. THE AMATEUR MECHANIC Just the book for the amateur mechanic who wants to know how to make, run and repair materials and ma- chines used in the home and farm. Illus. HOW TO FLY A non-technical account of just how an aeroplane is built and how it flies. Illus. THE HOME HANDY BOOK Invaluable in performing the thousand and one little jobs always turning up in the house. Illus. KEEPING UP WITH YOUR MOTOR CAR Here's a book that really enables you to keep your motor car in working condition. Illus. MOTOR CAR STARTING AND LIGHTING Everything one needs to know about starting, lighting and ignition systems. D. APPLETON AND COMPANY Publishers New York T712 t/ r7