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.Fig. 1.--Simple Receiving Set. Fig. 2.--Simple Transmitting Set.

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:

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.