The Radio Amateurs Hand Book | Page 8

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.
[Illustration: Fig. 1.--Simple Receiving 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:
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