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A very simple experimental short wave radio receiver. This
is basically just a crystal
radio with two stages of transistor amplification afterwards.
If I remember I used a pair of low impedance headphones with this
radio. They were the large types and had excellent sound insulation:
when you wore them you wouldn't hear much of what was going on
in the room. This probably helped to hear what must have been
some very quiet signals from this radio.
The diagram below shows an APPROXIMATE circuit diagram of this
radio, drawn by reference to the circuit board itself.
All the components are from scrap. Starting at the left of the
photograph, you can see two small coils on formers. One has 9 turns,
the other 6. They both have a ferrite slug which I adjusted to
get different frequency ranges. I could switch between the two
coils, giving two ranges. The radio was built on perforated
matrix board: but not the usual "modern" stuff with a 0.1-inch
matrix. This old board had 0.15-inch hole spacing. The variable
capacitor has a screw for attachment of a tuning knob, but I had
none so would vary it by turning the vanes of the by hand.
The two transistors are also scrap. They are the circular
black (BC153) and metallic (BF185) components in the photograph.
All the resistors and capacitors were junk too, the values
were chosen according to what came to hand rather than any
calculation. The components ahead of the first transistor
are unmarked; the fixed capacitor would have been of the order
of a few picofarads. The diode is a germanium type.
For an aerial, I strung a piece of wire from my bedroom window
at the top of the house to a clothes line pole at the end of the
garden, which was narrow and thin. It must have been around 120-150
feet of wire.
This very simple radio actually operated surprisingly well. I
spent many hours listening to the BBC World Service and the
Radio Moscow World Service (at that time, the English-speaking world
radio service of the former USSR). It was of great interest
to hear often differing views of the same world events.
