Solid State Shortwave Receivers For Beginners - The Listeners Guide

To those unfamiliar with this method of band changing it may
seem to be a little unusua1,but in fact, it is almost universaly used in
simple S.W. receiver designs, and is even employed in a few highly
sophisticated Sets. One thing it is, is very practical and this accounts
for its widespread adoption, and its recommended use with the
receiver circuits described here.
When using the specified 365 pF tuning capacitor the three
ranges have the approximate frequency coverage shown below: -
Range 3 l.5 to 5.5 MHZ
Range 4 5.0 to 17.0 MHZ
Range 5 10.0 to 35.5 MHZ
Note that these are only approximate, and the exact frequency
coverage of a receiver is influenced to some extent by the tolerances
of the components used and by stray capacitances present in the
circuit. It is also affected, and to a far greater extent, by the setting
of the adjustable core of each coil.
Some readers may be confused by the fact that some receiver
circuits shown in these pages use coils intended for valve circuits (the
D.P. coils) and some use coils intended for transistor circuits (those
that have a letter T after the range number), whereas all the designs
are solid state ones. This is because many of the designs use field
effect transistors (FETS) and these are very different to ordinary
bipolar transistors. The primary difference is that FETs haye
extremely high input impedances and so do valves, but dipolat transistors
havecomparatively low input impedances. Thus coils that are intended
for valved circuits can be easily and well adapted to FET circuits, whereas
coils that are intended for bipolar transistor circuits cannot.
The crystal set is really only designed to operate with a Range 4
coil, and this has the 49, 41, 31, 25 and 19 Metre broadcast bands within
its coverage. These provide the most prolific selection of stations when
using a very simple set such as this.
It is possible to use the Range 3 and Range 5 coils, and the set
will function just as well on these ranges, but good results are not likely
to be obtained as there are not such a large number of stations providing
suitable signals on these ranges. Reception of the ordinary M.W. broadcast
band can be provided by using a Range 2 coil.
A crystal set is not really suitable for amateur band reception as
amateur transmitters are restricted to a relatively low output power,
and this means that few, if any, signals of sufficient strength can be
received on these bands. Anyway, these days the majority of amateurs
use modes of transmission that cannot be resolved by a crystal set even
if a signal of adequate strengtl is received.
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