1-32
Figure 1-26A.—Key-click filters.
Figure 1-26B.—Key-click filters.
The capacitors and rf chokes in figure 1-26, views (A) and (B), prevent surges of current. In view
(B), the choke coil causes a lag in the current when the key is closed, and the current builds up gradually
instead of instantly. The capacitor charges as the key is opened and slowly releases the energy stored in
the magnetic field of the inductor. The resistor controls the rate of charge of the capacitor and also
prevents sparking at the key contacts by the sudden discharge of the capacitor when the key is closed.
MACHINE KEYING.—The speed with which information can be transmitted using a hand key
depends on the keying ability of the operator. Early communicators turned to mechanized methods of
keying the transmitters to speed transmissions. More information could be passed in a given time by
replacing the hand-operated key with a keying device capable of reading information from punched tape.
Using this method, several operators could prepare tapes at their normal operating speed. The tapes could
then be read through the keying device at a higher rate of speed and more information could be
transmitted in a given amount of time.
Spectrum Analysis
Continuous-wave transmission has the disadvantage of being a relatively slow transmission method.
Still, it has several advantages. Some of the advantages of cw transmission are a high degree of clarity
under severe noise conditions, long-range operation, and narrow bandwidth. A highly skilled operator can
pick out and read a cw signal even though it has a high degree of background noise or interference. Since
only a single-carrier frequency is being transmitted, all of the transmitter power can be concentrated in the
intelligence. This concentration of power gives the transmission a greater range. The use of spectrum
