How to Build Advanced Short Wave Receivers - The Listeners Guide

Note that shortness of wiring is more important on the higher
frequency ranges than it is on the lower frequency ones. It is
inevitable that the wiring to some coils will be longer than the
wiring to others, and so the layout should be arranged in such
a fashion that the shortest wiring connects to the Range 5T
coil.
Apart from the fact that long wires are likely to cause a greater
loss of efficiency on Range 5T there is the additional problem
that long leads in the wiring associated with the tuned windings
will significantly increase the inductance of these windings.
This can result in a loss of the extreme H.P. coverage of
the receiver and it can also cause problems with alignment.
If bandswitching is used it is possible to eliminate the mixer
trimmer control by adding a 10/40pf (approx.) trimmer
capacitor across the tuned winding of each mixer coil. It is
also necessary to remove the fixed capacitor connected across
the oscillator tuning capacitor, and then add a 10/40pf trimmer
across the tuned winding of each oscillator coil.
With the aid of a signal generator the oscillator trimmer is
adjusted to set the correct upper frequency limit of one tuning
range. Then the core of that oscillator coil is adjusted to
produce the correct lower frequency limit on that tuning
range. Then the trimmer is read to produce the proper
limit of H.P. coverage once again, and this whole procedure
is repeated several times until the correct coverage (or very
nearly so) is obtained.
Then the set is tuned to the high frequency end of the range
and the mixer trimmer is adjusted to peak sensitivity. Next the
set is tuned to the low frequency end of the range and the
core of the mixer coil is adjusted to peak sensitivity. The
receiver is then returned to the high frequency end of the
tuning range once again and the mixer trimmer is repeaked.
This procedure is repeated several times until no further
improvement in overall sensitivity can be obtained.
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