The Radio Amateur's Hand Book

In writing this book it is taken for granted that you are: first, one of the several hundred thousand persons in the United States who are interested in wireless telegraphy and telephony; second, that you would like to install an apparatus in your home, and third, that it is all new to you.

Now if you live in a city or town large enough to support an electrical supply store, there you will find the necessary apparatus on sale, and someone who can tell you what you want to know about it and how it works. If you live away from the marts and hives of industry you can send to various makers of wireless apparatus [Footnote: A list of makers of wireless apparatus will be found in the Appendix.] for their catalogues and price-lists and these will give you much useful information. But in either case it is the better plan for you to know before you start in to buy an outfit exactly what apparatus you need to produce the result you have in mind, and this you can gain in easy steps by reading this book.

Kinds of Wireless Systems.--There are two distinct kinds of wireless systems and these are: the wireless telegraph system, and the wireless telephone system. The difference between the wireless telegraph and the wireless telephone is that the former transmits messages by means of a telegraph key, and the latter transmits conversation and music by means of a microphone transmitter. In other words, the same difference exists between them in this respect as between the Morse telegraph and the Bell telephone.

Parts of a Wireless System.--Every complete wireless station, whether telegraph or telephone, consists of three chief separate and distinct parts and these are: (a) the aerial wire system, or antenna as it is often called, (b) the transmitter, or sender, and (c) the receiver, or, more properly, the receptor. The aerial wire is precisely the same for either wireless telegraphy or wireless telephony. The transmitter of a wireless telegraph set generally uses a spark gap for setting up the electric oscillations, while usually for wireless telephony a vacuum tube is employed for this purpose. The receptor for wireless telegraphy and telephony is the same and may include either a crystal detector or a vacuum tube detector, as will be explained presently.

The Easiest Way to Start.--First of all you must obtain a government license to operate a sending set, but you do not need a license to put up and use a receiving set, though you are required by law to keep secret any messages which you may overhear. Since no license is needed for a receiving set the easiest way to break into the wireless game is to put up an aerial and hook up a receiving set to it; you can then listen-in and hear what is going on in the all-pervading ether around you, and you will soon find enough to make things highly entertaining.

Nearly all the big wireless companies have great stations fitted with powerful telephone transmitters and at given hours of the day and night they send out songs by popular singers, dance music by jazz orchestras, fashion talks by and for the ladies, agricultural reports, government weather forecasts and other interesting features. Then by simply shifting the slide on your tuning coil you can often tune-in someone who is sending Morse, that is, messages in the dot and dash code, or, perhaps a friend who has a wireless telephone transmitter and is talking. Of course, if you want to talk back you must have a wireless transmitter, either telegraphic or telephonic, and this is a much more expensive part of the apparatus than the receptor, both in its initial cost and in its operation. A wireless telegraph transmitter is less costly than a wireless telephone transmitter and it is a very good scheme for you to learn to send and receive telegraphic messages.

At the present time, however, there are fifteen amateur receiving stations in the United States to every sending station, so you can see that the majority of wireless folks care more for listening in to the broadcasting of news and music than to sending out messages on their own account. The easiest way to begin wireless, then, is to put up an aerial and hook up a receiving set to it.

About Aerial Wire Systems.--To the beginner who wants to install a wireless station the aerial wire system usually looms up as the biggest obstacle of all, and especially is this true if his house is without a flag pole, or other elevation from which the aerial wire can be conveniently suspended.

If you live in the congested part of a big city where there are no yards and, particularly, if you live in a flat building or an apartment house, you will have to string your aerial wire on the roof, and to do this you should get the owner's, or agent's, permission. This is usually an easy thing to do where you only intend to receive messages, for one or two thin wires supported at either end of the building are all that are needed. If for any reason you cannot put your aerial on the roof then run a wire along the building outside of your apartment, and, finally, if this is not feasible, connect your receiver to a wire strung up in your room, or even to an iron or a brass bed, and you can still get the near-by stations.

An important part of the aerial wire system is the ground, that is, your receiving set must not only be connected with the aerial wire, but with a wire that leads to and makes good contact with the moist earth of the ground. Where a house or a building is piped for gas, water or steam, it is easy to make a ground connection, for all you have to do is to fasten the wire to one of the pipes with a clamp. [Footnote: Pipes are often insulated from the ground, which makes them useless for this purpose.] Where the house is isolated then a lot of wires or a sheet of copper or of zinc must be buried in the ground at a sufficient depth to insure their being kept moist.

About the Receiving Apparatus.--You can either buy the parts of the receiving apparatus separate and hook them up yourself, or you can buy the apparatus already assembled in a set which is, in the beginning, perhaps, the better way.

The simplest receiving set consists of (1) a detector, (2) a tuning coil, and (3) a telephone receiver and these three pieces of apparatus are, of course, connected together and are also connected to the aerial and ground as the diagram in Fig. 1 clearly shows. There are two chief kinds of detectors used at the present time and these are: (a) the crystal detector, and (b) the vacuum tube detector. The crystal detector is the cheapest and simplest, but it is not as sensitive as the vacuum tube detector and it requires frequent adjustment. A crystal detector can be used with or without a battery while the vacuum tube detector requires two small batteries.

A tuning coil of the simplest kind consists of a single layer of copper wire wound on a cylinder with an adjustable, or sliding, contact, but for sharp tuning you need a loose coupled tuning coil. Where a single coil tuner is used a fixed condenser should be connected around the telephone receivers. Where a loose coupled tuner is employed you should have a variable condenser connected across the closed oscillation circuit and a fixed condenser across the telephone receivers.

When listening-in to distant stations the energy of the received wireless waves is often so very feeble that in order to hear distinctly an amplifier must be used. To amplify the incoming sounds a vacuum tube made like a detector is used and sometimes as many as half-a-dozen of these tubes are connected in the receiving circuit, or in cascade, as it is called, when the sounds are amplified, that is magnified, many hundreds of times.

The telephone receiver of a receiving set is equally as important as the detector. A single receiver can be used but a pair of receivers connected with a head-band gives far better results. Then again the higher the resistance of the receivers the more sensitive they often are and those wound to as high a resistance as 3,200 ohms are made for use with the best sets. To make the incoming signals, conversation or music, audible to a room full of people instead of to just yourself you must use what is called a loud speaker. In its simplest form this consists of a metal cone like a megaphone to which is fitted a telephone receiver.

About Transmitting Stations--Getting Your License.--If you are going to install a wireless sending apparatus, either telegraphic or telephonic, you will have to secure a government license for which no fee or charge of any kind is made. There are three classes of licenses issued to amateurs who want to operate transmitting stations and these are: (1) the restricted amateur license, (2) the general amateur license, and (3) the special amateur license.

If you are going to set up a transmitter within five nautical miles of any naval wireless station then you will have to get a restricted amateur license which limits the current you use to half a kilowatt [Footnote: A Kilowatt is 1,000 watts. There are 746 watts in a horsepower.] and the wave length you send out to 200 meters. Should you live outside of the five-mile range of a navy station then you can get a general amateur license and this permits you to use a current of 1 kilowatt, but you are likewise limited to a wave length of 200 meters. But if you can show that you are doing some special kind of wireless work and not using your sending station for the mere pleasure you are getting out of it you may be able to get a special amateur license which gives you the right to send out wave lengths up to 375 meters.

When you are ready to apply for your license write to the Radio Inspector of whichever one of the following districts you live in:

First District..............Boston, Mass.

Second " ..............New York City

Third " ..............Baltimore, Md.

Fourth " ..............Norfolk, Va.

Fifth " ..............New Orleans, La.

Sixth " ............. San Francisco, Cal.

Seventh " ............. Seattle, Wash.

Eighth " ............. Detroit, Mich.

Ninth " ..............Chicago, Ill.

Kinds of Transmitters.--There are two general types of transmitters used for sending out wireless messages and these are: (1) wireless telegraph transmitters, and (2) wireless telephone transmitters. Telegraph transmitters may use either: (a) a jump-spark, (b) an electric arc, or (c) a vacuum tube apparatus for sending out dot and dash messages, while telephone transmitters may use either, (a) an electric arc, or (b) a vacuum tube for sending out vocal and musical sounds. Amateurs generally use a jump-spark for sending wireless telegraph messages and the vacuum tube for sending wireless telephone messages.

The Spark Gap Wireless Telegraph Transmitter.--The simplest kind of a wireless telegraph transmitter consists of: (1) a source of direct or alternating current, (2) a telegraph key, (3) a spark-coil or a transformer, (4) a spark gap, (5) an adjustable condenser and (6) an oscillation transformer. Where dry cells or a storage battery must be used to supply the current for energizing the transmitter a spark-coil can be employed and these may be had in various sizes from a little fellow which gives 1/4-inch spark up to a larger one which gives a 6-inch spark. Where more energy is needed it is better practice to use a transformer and this can be worked on an alternating current of 110 volts, or if only a 110 volt direct current is available then an electrolytic interrupter must be used to make and break the current. A simple transmitting set with an induction coil is shown in Fig. 2.

A wireless key is made like an ordinary telegraph key except that where large currents are to be used it is somewhat heavier and is provided with large silver contact points. Spark gaps for amateur work are usually of: (1) the plain or stationary type, (2) the rotating type, and (3) the quenched gap type. The plain spark-gap is more suitable for small spark-coil sets, and it is not so apt to break down the transformer and condenser of the larger sets as the rotary gap. The rotary gap on the other hand tends to prevent arcing and so the break is quicker and there is less dragging of the spark. The quenched gap is more efficient than either the plain or rotary gap and moreover it is noiseless.

Condensers for spark telegraph transmitters can be ordinary Leyden jars or glass plates coated with tin or copper foil and set into a frame, or they can be built up of mica and sheet metal embedded in an insulating composition. The glass plate condensers are the cheapest and will serve your purpose well, especially if they are immersed in oil. Tuning coils, sometimes called transmitting inductances and oscillation transformers, are of various types. The simplest kind is a transmitting inductance which consists of 25 or 30 turns of copper wire wound on an insulating tube or frame. An oscillation transformer is a loose coupled tuning coil and it consists of a primary coil formed of a number of turns of copper wire wound on a fixed insulating support, and a secondary coil of about twice the number of turns of copper wire which is likewise fixed in an insulating support, but the coils are relatively movable. An oscillation transformer (instead of a tuning coil), is required by government regulations unless inductively coupled.

The Vacuum Tube Telegraph Transmitter.--This consists of: (1) a source of direct or alternating current, (2) a telegraph key, (3) a vacuum tube oscillator, (4) a tuning coil, and (5) a condenser. This kind of a transmitter sets up sustained oscillations instead of periodic oscillations which are produced by a spark gap set. The advantages of this kind of a system will be found explained in Chapter XVI.

The Wireless Telephone Transmitter.--Because a jump-spark sets up periodic oscillations, that is, the oscillations are discontinuous, it cannot be used for wireless telephony. An electric arc or a vacuum tube sets up sustained oscillations, that is, oscillations which are continuous. As it is far easier to keep the oscillations going with a vacuum tube than it is with an arc the former means has all but supplanted the latter for wireless telephone transmitters. The apparatus required and the connections used for wireless telephone sets will be described in later chapters.

Useful Information.--It would be wise for the reader to turn to the Appendix, beginning with page 301 of this book, and familiarize himself with the information there set down in tabular and graphic form. For example, the first table gives abbreviations of electrical terms which are in general use in all works dealing with the subject. You will also find there brief definitions of electric and magnetic units, which it would be well to commit to memory; or, at least, to make so thoroughly your own that when any of these terms is mentioned, you will know instantly what is being talked about.

As inferred in the first chapter, an aerial for receiving does not have to be nearly as well made or put up as one for sending. But this does not mean that you can slipshod the construction and installation of it, for however simple it is, the job must be done right and in this case it is as easy to do it right as wrong.

To send wireless telegraph and telephone messages to the greatest distances and to receive them as distinctly as possible from the greatest distances you must use for your aerial (1) copper or aluminum wire, (2) two or more wires, (3) have them the proper length, (4) have them as high in the air as you can, (5) have them well apart from each other, and (6) have them well insulated from their supports. If you live in a flat building or an apartment house you can string your aerial wires from one edge of the roof to the other and support them by wooden stays as high above it as may be convenient.

Should you live in a detached house in the city you can usually get your next-door neighbor to let you fasten one end of the aerial to his house and this will give you a good stretch and a fairly high aerial. In the country you can stretch your wires between the house and barn or the windmill. From this you will see that no matter where you live you can nearly always find ways and means of putting up an aerial that will serve your needs without going to the expense of erecting a mast.

Kinds of Aerial Wire Systems.--An amateur wireless aerial can be anywhere from 25 feet to 100 feet long and if you can get a stretch of the latter length and a height of from 30 to 75 feet you will have one with which you can receive a thousand miles or more and send out as much energy as the government will allow you to send.

The kind of an aerial that gives the best results is one whose wire, or wires, are horizontal, that is, parallel with the earth under it as shown at A in Fig. 3. If only one end can be fixed to some elevated support then you can secure the other end to a post in the ground, but the slope of the aerial should not be more than 30 or 35 degrees from the horizontal at most as shown at B.

The leading-in wire, that is, the wire that leads from and joins the aerial wire with your sending and receiving set, can be connected to the aerial anywhere it is most convenient to do so, but the best results are had when it is connected to one end as shown at A in Fig. 4, in which case it is called an inverted L aerial, or when it is connected to it at the middle as shown at B, when it is called a T aerial. The leading-in wire must be carefully insulated from the outside of the building and also where it passes through it to the inside. This is done by means of an insulating tube known as a leading-in insulator, or bulkhead insulator as it is sometimes called.

As a protection against lightning burning out your instruments you can use either: (1) an air-gap lightning arrester, (2) a vacuum tube protector, or (3) a lightning switch, which is better. Whichever of these devices is used it is connected in between the aerial and an outside ground wire so that a direct circuit to the earth will be provided at all times except when you are sending or receiving. So your aerial instead of being a menace really acts during an electrical storm like a lightning rod and it is therefore a real protection. The air-gap and vacuum tube lightning arresters are little devices that can be used only where you are going to receive, while the lightning switch must be used where you are going to send; indeed, in some localities the Fire Underwriters require a large lightning switch to be used for receiving sets as well as sending sets.

How to Put Up a Cheap Receiving Aerial.--The kind of an aerial wire system you put up will depend, chiefly, on two things, and these are: (1) your pocketbook, and (2) the place where you live.

A Single Wire Aerial.--This is the simplest and cheapest kind of a receiving aerial that can be put up. The first thing to do is to find out the length of wire you need by measuring the span between the two points of support; then add a sufficient length for the leading-in wire and enough more to connect your receiving set with the radiator or water pipe.

You can use any size of copper or aluminum wire that is not smaller than No. 16 Brown and Sharpe gauge. When you buy the wire get also the following material: (1) two porcelain insulators as shown at A in Fig. 5; (2) three or four porcelain knob insulators, see B; (3) either (a) an air gap lightning arrester, see C, or (b) a lightning switch see D; (4) a leading-in porcelain tube insulator, see E, and (5) a ground clamp, see F.

To make the aerial slip each end of the wire through a hole in each insulator and twist it fast; next cut off and slip two more pieces of wire through the other holes in the insulators and twist them fast and then secure these to the supports at the ends of the building. Take the piece you are going to use for the leading-in wire, twist it around the aerial wire and solder it there when it will look like A in Fig. 6. Now if you intend to use the air gap lightning arrester fasten it to the wall of the building outside of your window, and bring the leading-in wire from the aerial to the top binding post of your arrester and keep it clear of everything as shown at B. If your aerial is on the roof and you have to bring the leading-in wire over the cornice or around a corner fix a porcelain knob insulator to the one or the other and fasten the wire to it.

Next bore a hole through the frame of the window at a point nearest your receiving set and push a porcelain tube 5/8 inch in diameter and 5 or 6 inches long, through it. Connect a length of wire to the top post of the arrester or just above it to the wire, run this through the leading-in insulator and connect it to the slider of your tuning coil. Screw the end of a piece of heavy copper wire to the lower post of the arrester and run it to the ground, on porcelain knobs if necessary, and solder it to an iron rod or pipe which you have driven into the earth. Finally connect the fixed terminal of your tuning coil with the water pipe or radiator inside of the house by means of the ground clamp as shown in the diagrammatic sketch at B in Fig. 6 and you are ready to tune in.

If you want to use a lightning switch instead of the air-gap arrester then fasten it to the outside wall instead of the latter and screw the free end of the leading-in wire from the aerial to the middle post of it as shown at C in Fig. 6. Run a wire from the top post through the leading-in insulator and connect it with the slider of your tuning coil. Next screw one end of a length of heavy copper wire to the lower post of the aerial switch and run it to an iron pipe in the ground as described above in connection with the spark-gap lightning arrester; then connect the fixed terminal of your tuning coil with the radiator or water pipe and your aerial wire system will be complete as shown at C in Fig. 6.

A Two-wire Aerial.--An aerial with two wires will give better results than a single wire and three wires are better than two, but you must keep them well apart. To put up a two-wire aerial get (1) enough No. 16, or preferably No. 14, solid or stranded copper or aluminum wire, (2) four porcelain insulators, see B in Fig. 5, and (3) two sticks about 1 inch thick, 3 inches wide and 3 or 4 feet long, for the spreaders, and bore 1/8-inch hole through each end of each one. Now twist the ends of the wires to the insulators and then cut off four pieces of wire about 6 feet long and run them through the holes in the wood spreaders. Finally twist the ends of each pair of short wires to the free ends of the insulators and then twist the free ends of the wires together.

For the leading-in wire that goes to the lightning switch take two lengths of wire and twist one end of each one around the aerial wires and solder them there. Twist the short wire around the long wire and solder this joint also when the aerial will look like Fig. 7. Bring the free end of the leading-in wire down to the middle post of the lightning switch and fasten it there and connect up the receiver to it and the ground as described under the caption of A Single Wire Aerial.

Connecting in the Ground.--If there is a gas or water system or a steam-heating plant in your house you can make your ground connection by clamping a ground clamp to the nearest pipe as has been previously described. Connect a length of bare or insulated copper wire with it and bring this up to the table on which you have your receiving set. If there are no grounded pipes available then you will have to make a good ground which we shall describe presently and lead the ground wire from your receiving set out of the window and down to it.

How to Put Up a Good Aerial.--While you can use the cheap aerial already described for a small spark-coil sending set you should have a better insulated one for a 1/2 or a 1 kilowatt transformer set. The cost for the materials for a good aerial is small and when properly made and well insulated it will give results that are all out of proportion to the cost of it.

An Inexpensive Good Aerial.--A far better aerial, because it is more highly insulated, can be made by using midget insulators instead of the porcelain insulators described under the caption of A Single Wire Aerial and using a small electrose leading-in insulator instead of the porcelain bushing. This makes a good sending aerial for small sets as well as a good receiving aerial.

The Best Aerial that Can Be Made.--To make this aerial get the following material together: (1) enough stranded or braided wire for three or four lengths of parallel wires, according to the number you want to use (2) six or eight electrose ball insulators, see B, Fig. 8; (3) two 5-inch or 10-inch electrose strain insulators, see C; (4) six or eight S-hooks, see D; one large withe with one eye for middle of end spreader, see E; (6) two smaller withes with one eye each for end spreader, see E; (7) two still smaller withes, with two eyes each for the ends of the end spreaders, see E (8) two thimbles, see F, for 1/4-inch wire cable; (9) six or eight hard rubber tubes or bushings as shown at G; and (10) two end spreaders, see H; one middle spreader, see I; and one leading-in spreader, see J.

For this aerial any one of a number of kinds of wire can be used and among these are (a) stranded copper wire; (b) braided copper wire; (c) stranded silicon bronze wire, and (d) stranded phosphor bronze wire. Stranded and braided copper wire is very flexible as it is formed of seven strands of fine wire twisted or braided together and it is very good for short and light aerials. Silicon bronze wire is stronger than copper wire and should be used where aerials are more than 100 feet long, while phosphor bronze wire is the strongest aerial wire made and is used for high grade aerials by the commercial companies and the Government for their high-power stations.

The spreaders should be made of spruce, and should be 4 feet 10 inches long for a three-wire aerial and 7 feet 1 inch long for a four-wire aerial as the distance between the wires should be about 27 inches. The end spreaders can be turned cylindrically but it makes a better looking job if they taper from the middle to the ends. They should be 2-1/4 inches in diameter at the middle and 1-3/4 inches at the ends. The middle spreader can be cylindrical and 2 inches in diameter. It must have holes bored through it at equidistant points for the hard rubber tubes; each of these should be 5/8 inch in diameter and have a hole 5/32 inch in diameter through it for the aerial wire. The leading-in spreader is also made of spruce and is 1-1/2 inches square and 26 inches long. Bore three or four 5/8-inch holes at equidistant points through this spreader and insert hard rubber tubes in them as with the middle spreader.

Assembling the Aerial.--Begin by measuring off the length of each wire to be used and see to it that all of them are of exactly the same length. Now push the hard rubber insulators through the holes in the middle spreader and thread the wires through the holes in the insulators as shown at A in Fig 9.

Next twist the ends of each wire to the rings of the ball insulators and then put the large withes on the middle of each of the end spreaders; fix the other withes on the spreaders so that they will be 27 inches apart and fasten the ball insulators to the eyes in the withes with the S-hooks. Now slip a thimble through the eye of one of the long strain insulators, thread a length of stranded steel wire 1/4 inch in diameter through it and fasten the ends of it to the eyes in the withes on the ends of the spreaders.

Finally fasten a 40-inch length of steel stranded wire to each of the eyes of the withes on the middle of each of the spreaders, loop the other end over the thimble and then wrap the end around the wires that are fixed to the ends of the spreaders. One end of the aerial is shown complete at B in Fig. 9, and from this you can see exactly how it is assembled. Now cut off three or four pieces of wire 15 or 20 feet long and twist and solder each one to one of the aerial wires; then slip them through the hard rubber tubes in the leading-in spreader, bring their free ends together as at C and twist and solder them to a length of wire long enough to reach to your lightning switch or instruments.

Making a Good Ground.--Where you have to make a ground you can do so either by (1) burying sheets of zinc or copper in the moist earth; (2) burying a number of wires in the moist earth, or (3) using a counterpoise. To make a ground of the first kind take half a dozen large sheets of copper or zinc, cut them into strips a foot wide, solder them all together with other strips and bury them deeply in the ground.

It is easier to make a wire ground, say of as many or more wires as you have in your aerial and connect them together with cross wires. To put such a ground in the earth you will have to use a plow to make the furrows deep enough to insure them always being moist. In the counterpoise ground you make up a system of wires exactly like your aerial, that is, you insulate them just as carefully; then you support them so that they will be as close to the ground as possible and yet not touch it or anything else. This and the other two grounds just described should be placed directly under the aerial wire if the best results are to be had. In using a counterpoise you must bring the wire from it up to and through another leading-in insulator to your instruments.

With a crystal detector receiving set you can receive either telegraphic dots and dashes or telephonic speech and music. You can buy a receiving set already assembled or you can buy the different parts and assemble them yourself. An assembled set is less bother in the beginning but if you like to experiment you can hook up, that is, connect the separate parts together yourself and it is perhaps a little cheaper to do it this way. Then again, by so doing you get a lot of valuable experience in wireless work and an understanding of the workings of wireless that you cannot get in any other way.

Assembled Wireless Receiving Sets.--The cheapest assembled receiving set [Footnote: The Marvel, made by the Radio Mfg. Co., New York City.] advertised is one in which the detector and tuning coil is mounted in a box. It costs $15.00, and can be bought of dealers in electric supplies generally.

This price also includes a crystal detector, an adjustable tuning coil, a single telephone receiver with head-band and the wire, porcelain insulators, lightning switch and ground clamp for the aerial wire system. It will receive wireless telegraph and telephone messages over a range of from 10 to 25 miles.

Another cheap unit receptor, that is, a complete wireless receiving set already mounted which can be used with a single aerial is sold for $25.00. [Footnote: The Aeriola Jr., made by the Westinghouse Company, Pittsburgh, Pa.] This set includes a crystal detector, a variable tuning coil, a fixed condenser and a pair of head telephone receivers. It can also be used to receive either telegraph or telephone messages from distances up to 25 miles. The aerial equipment is not included in this price, but it can be bought for about $2.50 extra.

Assembling Your Own Receiving Set.--In this chapter we shall go only into the apparatus used for two simple receiving sets, both of which have a crystal detector. The first set includes a double-slide tuning coil and the second set employs a loose-coupled tuning coil, or loose coupler, as it is called for short. For either set you can use a pair of 2,000- or 3,000-ohm head phones.

Photograph unavailable

original ? Underwood and Underwood.

General Pershing Listening In.

The Crystal Detector.--A crystal detector consists of: (1) the frame, (2) the crystal, and (3) the wire point. There are any number of different designs for frames, the idea being to provide a device that will (a) hold the sensitive crystal firmly in place, and yet permit of its removal, (b) to permit the wire point, or electrode, to be moved in any direction so that the free point of it can make contact with the most sensitive spot on the crystal and (c) to vary the pressure of the wire on the crystal.

A simple detector frame is shown in the cross-section at A in Fig. 10; the crystal, which may be galena, silicon or iron pyrites, is held securely in a holder while the phosphor-bronze wire point which makes contact with it, is fixed to one end of a threaded rod on the other end of which is a knob. This rod screws into and through a sleeve fixed to a ball that sets between two brass standards and this permits an up and down or a side to side adjustment of the metal point while the pressure of it on the crystal is regulated by the screw.

A crystal of this kind is often enclosed in a glass cylinder and this makes it retain its sensitiveness for a much longer time than if it were exposed to dust and moisture. An upright type of this detector can be bought for $2.25, while a horizontal type, as shown at B, can be bought for $2.75. Galena is the crystal that is generally used, for, while it is not quite as sensitive as silicon and iron pyrites, it is easier to obtain a sensitive piece.

The Tuning Coil.--It is with the tuning coil that you tune in and tune out different stations and this you do by sliding the contacts to and fro over the turns of wire; in this way you vary the inductance and capacitance, that is, the constants of the receiving circuits and so make them receive electric waves, that is, wireless waves, of different lengths.

The Double Slide Tuning Coil.--With this tuning coil you can receive waves from any station up to 1,000 meters in length. One of the ends of the coil of wire connects with the binding post marked a in Fig. 11, and the other end connects with the other binding post marked b, while one of the sliding contacts is connected to the binding post c, and the other sliding contact is connected with the binding post d.

When connecting in the tuning coil, only the post a or the post b is used as may be most convenient, but the other end of the wire which is connected to a post is left free; just bear this point in mind when you come to connect the tuning coil up with the other parts of your receiving set. The tuning coil is shown complete at B and it costs $3.00 or $4.00. A triple slide tuning coil constructed like the double slide tuner just described, only with more turns of wire on it, makes it possible to receive wave lengths up to 1,500 meters. It costs about $6.00.

The Loose Coupled Tuning Coil.--With a loose coupler, as this kind of a tuning coil is called for short, very selective tuning is possible, which means that you can tune in a station very sharply, and it will receive any wave lengths according to size of coils. The primary coil is wound on a fixed cylinder and its inductance is varied by means of a sliding contact like the double slide tuning coil described above. The secondary coil is wound on a cylinder that slides in and out of the primary coil. The inductance of this coil is varied by means of a switch that makes contact with the fixed points, each of which is connected with every twentieth turn of wire as shown in the diagram A in Fig. 12. The loose coupler, which is shown complete at B, costs in the neighborhood of $8.00 or $10.00.

Fixed and Variable Condensers.--You do not require a condenser for a simple receiving set, but if you will connect a fixed condenser across your headphones you will get better results, while a variable condenser connected in the closed circuit of a direct coupled receiving set, that is, one where a double slide tuning coil is used, makes it easy to tune very much more sharply; a variable condenser is absolutely necessary where the circuits are inductively coupled, that is, where a loose coupled tuner is used.

A fixed condenser consists of a number of sheets of paper with leaves of tin-foil in between them and so built up that one end of every other leaf of tin-foil projects from the opposite end of the paper as shown at A in Fig. 13. The paper and tin-foil are then pressed together and impregnated with an insulating compound. A fixed condenser of the exact capacitance required for connecting across the head phones is mounted in a base fitted with binding posts, as shown at B, and costs 75 cents. (Paper ones 25 cents.)

A variable condenser, see C, of the rotating type is formed of a set of fixed semi-circular metal plates which are slightly separated from each other and between these a similar set of movable semi-circular metal plates is made to interleave; the latter are secured to a shaft on the top end of which is a knob and by turning it the capacitance of the condenser, and, hence, of the circuit in which it is connected, is varied. This condenser, which is shown at D, is made in two sizes, the smaller one being large enough for all ordinary wave lengths while the larger one is for proportionately longer wave lengths. These condensers cost $4.00 and $5.00 respectively.

About Telephone Receivers.--There are a number of makes of head telephone receivers on the market that are designed especially for wireless work. These phones are wound to resistances of from 75 ohms to 8,000 ohms, and cost from $1.25 for a receiver without a cord or headband to $15.00 for a pair of phones with a cord and head band. You can get a receiver wound to any resistance in between the above values but for either of the simple receiving sets such as described in this chapter you ought to have a pair wound to at least 2,000 ohms and these will cost you about $5.00. A pair of head phones of this type is shown in Fig. 14.

Connecting Up the Parts--Receiving Set No. 1.--For this set get (1) a crystal detector, (2) a two-slide tuning coil, (3) a fixed condenser, and (4) a pair of 2,000 ohm head phones. Mount the detector on the right-hand side of a board and the tuning coil on the left-hand side. Screw in two binding posts for the cord ends of the telephone receivers at a and b as shown at A in Fig. 15. This done connect one of the end binding posts of the tuning coil with the ground wire and a post of one of the contact slides with the lightning arrester or switch which leads to the aerial wire.

Now connect the post of the other contact slide to one of the posts of the detector and the other post of the latter with the binding post a, then connect the binding post b to the ground wire and solder the joint. Next connect the ends of the telephone receiver cord to the posts a and b and connect a fixed condenser also with these posts, all of which are shown in the wiring diagram at B, and you are ready to adjust the set for receiving.

Receiving Set No. 2.--Use the same kind of a detector and pair of head phones as for Set No. 1, but get (1) a loose coupled tuning coil, and (2) a variable condenser. Mount the loose coupler at the back of a board on the left-hand side and the variable condenser on the right-hand side. Then mount the detector in front of the variable condenser and screw two binding posts, a and b, in front of the tuning coil as shown at A in Fig. 16.

Now connect the post of the sliding contact of the loose coupler with the wire that runs to the lightning switch and thence to the aerial; connect the post of the primary coil, which is the outside coil, with the ground wire; then connect the binding post leading to the switch of the secondary coil, which is the inside coil, with one of the posts of the variable condenser, and finally, connect the post that is joined to one end of the secondary coil with the other post of the variable condenser.

This done, connect one of the posts of the condenser with one of the posts of the detector, the other post of the detector with the binding post a, and the post b to the other post of the variable condenser. Next connect a fixed condenser to the binding posts a and b and then connect the telephone receivers to these same posts, all of which is shown in the wiring diagram at B. You are now ready to adjust the instruments. In making the connections use No. 16 or 18 insulated copper wire and scrape the ends clean where they go into the binding posts. See, also, that all of the connections are tight and where you have to cross the wires keep them apart by an inch or so and always cross them at right angles.

Adjusting the No. 1 Set--The Detector.--The first thing to do is to test the detector in order to find out if the point of the contact wire is on a sensitive spot of the crystal. To do this you need a buzzer, a switch and a dry cell. An electric bell from which the gong has been removed will do for the buzzer, but you can get one that is made specially for the purpose, for 75 cents, which gives out a clear, high-pitched note that sounds like a high-power station.

Connect one of the binding posts of the buzzer with one post of the switch, the other post of the latter with the zinc post of the dry cell and the carbon post of this to the other post of the buzzer. Then connect the post of the buzzer that is joined to the vibrator, to the ground wire as shown in the wiring diagram, Fig. 17. Now close the switch of the buzzer circuit, put on your head phones, and move the wire point of the detector to various spots on the crystal until you hear the sparks made by the buzzer in your phones.

Then vary the pressure of the point on the crystal until you hear the sparks as loud as possible. After you have made the adjustment open the switch and disconnect the buzzer wire from the ground wire of your set. This done, be very careful not to jar the detector or you will throw it out of adjustment and then you will have to do it all over again. You are now ready to tune the set with the tuning coil and listen in.

The Tuning Coil.--To tune this set move the slide A of the double-slide tuner, see B in Fig. 15, over to the end of the coil that is connected with the ground wire and the slide B near the opposite end of the coil, that is, the one that has the free end. Now move the slide A toward the B slide and when you hear the dots and dashes, or speech or music, that is coming in as loud as you can move the B slide toward the A slide until you hear still more loudly. A very few trials on your part and you will be able to tune in or tune out any station you can hear, if not too close or powerful.

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original ? Underwood and Underwood.

The World's Largest Radio Receiving Station. Owned by the Radio Corporation of America at Rocky Point near Point Jefferson, L.I.

Adjusting the No. 2 Set.--First adjust the crystal detector with the buzzer set as described above with Set No. 1, then turn the knob of your variable condenser so that the movable plates are just half-way in, pull the secondary coil of your loose-coupled tuner half way out; turn the switch lever on it until it makes a contact with the middle contact point and set the slider of the primary coil half way between the ends.

Now listen in for telegraphic signals or telephonic speech or music; when you hear one or the other slide the secondary coil in and out of the primary coil until the sounds are loudest; now move the contact switch over the points forth and back until the sounds are still louder, then move the slider to and fro until the sounds are yet louder and, finally, turn the knob of the condenser until the sounds are clear and crisp. When you have done all of these things you have, in the parlance of the wireless operator, tuned in and you are ready to receive whatever is being sent.