Solid State Shortwave Receivers For Beginners - The Listeners Guide

As should be apparent by now, if the oscillator tuning is not
correct, the correct audio frequencies are not produced. If the oscillator
is not adjusted quite close enough to the sideband frequencies, all the
audio output frequencies will be too high in pitch.. Conversely, if it is
taken too close to the sideband signal the audio output will be too low
in pitch. Small errors in the oscillator frequency will not matter too
much, and the audio output will still be quite intelligible. What is not
satisfactory is if the oscillator frequency is put the wrong side of the
sideband signal. This results in all the audio signals being inverted, with
the high notes coming out as bass ones, and vice versa.
When tuning in a S.S.B. signal one should slowly tune towards it.
If it being approached from the correct side, the audio, pitch will
gradually fall to correct level. If it is being approached from the wrong
side the audio signal will remain completely unintelligible, and it will be
necessary to tune through the signal, and then tune towards it from the
correct side.
C.W. Signals
A C.W. signal is merely a carrier wave which is turned on and off
by way of a morse key. Morse is, of course, the form of modulation
used on the carrier wave. To produce an audio output from this type
of signal using a product detector is perfectly straight forward. If the
oscillator is tuned 1kHZ away from the carrier frequency, an audio
output at 1kHZ will be produced. If it is tuned closer than this the
audio pitch will drop, if it is tuned further away the audio pitch will
rise. it is simply a matter of adjusting the tuning to produce the desired
audio note. It does not matter which side of the carrier wave the
oscillator is adjusted.
An advantage of S.S.B. over A.M. is that it takes up less than half
the bandwidth for identical audio signals. C.W. occupies even less space.
S.S.B. and C.W. also make the most of the available transmitter power,
as the whole of the signal that is transmitted is carrying information.
In the case of A.M., the carrier wave itself does not contain any information,
this is present in the sidebands.
Amateur transmitters are limited to relatively modest output
powers, and the S.W. amateur bands are usually extremely crowded. It
is therefore no surprising that A.M. has almost completely died out on
the amateur bands.
Note that it is possible to tune S.S.B. and C.W. transmissions
satisfactorily on the receivers described so far, except where it has been
stated otherwise in the relevant receiver description. The regeneration
control is advanced slightly beyond the threshold of oscillation, and then
C.W. and S.S.B. signals can be tuned in the usual way. The oscillations
of the detector replace the missing carrier wave and an acceptable audio
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