Solid State Shortwave Receivers For Beginners - The Listeners Guide

crystal set is not very high. This particularly so when the aerial is
plugged into SK2, as the aerial then has a strong loading effect on the
tuned circuit; and its efficiency is severely reduced. Thus even though
stronger signals will be produced by plugging the aerial into SK2, and
there is a strong temptation to simply ignore SK1, the greater selectivity
obtained with the aerial connected to SK1 makes this the better of the
two most of the time. Only use SK2 when conditions are such that
only very weak signals are obtained when using SK1.
A degree of patience is required in order to obtain good results
from any S.W. Receiver, but this is especially so in the case of a S.W.
set. Stations temporarily fading out completely is one problem, and
another is that one station on the band can suddenly become exceptionally
strong, and blot out reception of the desired transmission, eventhough
it is at a good strength.
Despite its deficiencies, a lot of fun can be had from a crystal
set, and stations some thousands of miles away can be received if one
perseveres.
Regenerative Receiver
Unlike the crystal set, most receivers have a large amount of gain.
This enables very weak signals to be boosted to a level that produces a
good level of volume from the transducer. It also enables the selectivity
of the receiver to be greatly improved, and this is just as important as
the increased sensitivity.
One of the most widely used types of detector in simple S.W.
receivers is the regenerative detector. Basically this just consists of a
transistor (or other active device) in one of its normal amplifying modes.
A capacitor is connected across the output, as it is in the case of a diode
detector, to remove the R.F. content at the output of the detector.
It may not be immediately obvious how this arrangement
provides rectification, and in fact this type of detector may seem to be
a little unusual to those who are not familiar with the technique
employed. It relies upon the fact that no contemporary amplifying
devices are completely linear in operation, and the gain of an ordinary
transistor for instance, tends to rise with increasing collector ciurrent.
If it Is used to amplify an R.F. signal it will therefore tend to
amplify one set of half cycles more than the other set. It will amplify -
the positive input half cycles more than the negative ones. This provides
a very crude and inefficient form of rectification, and of course, it is
rectification that the detector must provide.
Regeneration is applied to the circuit in order to greatly increase
the detection efficiency of the circuit. Regeneration is merely positive
feedback or sending some of the signal bock from the output to the
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