Solid State Shortwave Receivers For Beginners - The Listeners Guide

Wire the completed Veroboard panel to the rest of the circuit
using ordinary multistand P.V.C. insulated connecting, and then mount
it on the underside of the chassis. Some spacers or extra nuts must be
used to space the panel well clear of the metal chassis, as otherwise the
connections on the reverse side of the panel will be short circuited
through the chassis.
Using the Receiver
This receiver is primarily intended for use on the broadcast
bands using the Range 4T and 5T coils. It will not work very efficiently
using a Range 3T coil, except towards the high frequency end of the
band where a number of stations on the 60 Metre broadcast band can
be received.
The tuning on on/off controls are quite conventional, but the
reaction controls are not volume controls, and they require very careful
adjustment if really good results are to be obtained from the
receiver.
The detector will operate most efficiently with VR1 turned well
back (i.e. adjusted almost fully anticlockwise), as it is then that the
difference in the levels of amplification given to each set of half cycles
is most unequal. Therefore VR1 should be kept well backed off and
VC2 is advanced to just below the threshold of oscillation. It should
perhaps be explained that by advancing VC2, it is meant that the two
sets of vanes should be more fully meshed together.
It is with the detector set just below the threshold of oscillation
that the set has the highest degree of sensitivity and selectivity. Adjusting
VC2 too far will result in the receiver breaking into oscillation, and
the practical result of this will be that a whistle of varying pitch will be
heard as the receiver is tuned across a station, and proper reception will
not be possible with the receiver in this condition.
Fine adjustment of the reaction level is probably best carried
out using VR1. This does not control the amount of feedback, but
affects the gain of Tr1, and this permits it to be used as a reaction
control. It will not provide anything like the degree of control that is
available using VC2, but it is this that makes it so much better for
making the fine adjustments of the regeneration level.
Towards the low frequency end of each band (VC1 vanes well
meshed) it will almost certainly be found that the detector cannot be
brought to the threshold of oscillation with VR1 turned well back. It
is then necessary to advance VR1 somewhat. This does reduce the
detection efficiency of the set, but the gain of the detector is increased.
This increased gain tends to compensate to some degree for the loss of
efficiency, and good results should still be obtained.
34