The Radio Amateurs Hand Book | Page 9

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.
[Illustration: Fig 2.--Simple Transmitting Set.]
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