The Spark Gap Wireless Telegraph Transmitter
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_, Obidia Porras K26fo 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_.