Choccy Block Transistor Radio Modifications
Other More Advanced Projects and
Modifications
Long Wave
There is nothing
to stop you making a LW coil to make a long wave radio, but
you'll need about 180 turns of wire wound up in three or more
layers. This can be quite bulky when made with PVC covered wire,
so you might choose to use thinner enameled copper wire or a
ready-made LW coil. It's relatively easy to connect one end of
both coils together and arrange a switch to connect either one
of the other ends to the tuning capacitor.
Short Wave
The pictures shown above are from the alternative breadboard
version but the effect is the same.
If you remove the ferrite rod, make the main coil about 25
turns and wind the coupling coils as shown in the picture, you
will be able to tune the shortwave bands from about 7 to
30MHz. At this stage you will need to link in a few meters of
aerial wire by connecting it to one end of the short coil on
the left and connecting the other end of the short coil to a
heating radiator or earth connection. Don't connect to a mains
power earth pin. The tuning will be quite broad but you will
be able to hear several strong international broadcasters,
especially after dark. Sliding the ferrite rod back in will
lower the frequency range of the tuning.
More Signal
One way of
sharpening up the tuning and getting more signal on the station
that you want is to use an external tuned loop antenna. This
requires no physical connection to the radio and can be very
effective. You can see how to make one here: Tuned
MW Loop Antenna. You should use a separate external
capacitor to tune the other loop.
General Magnetic Pickup
I've not given this a proper try
yet, but because our
radio only has one tuned circuit, it is quite easy to change it
to pick up other magnetic signals that are around in the
environment, and we can choose to have a high-Q tuned circuit or
not. We can also choose whether to have an AM demodulator or
not. It's easier when playing around with magnetic pickup if you
use headphones instead of the loudspeaker, as the strong signal
from the coil in the speaker has an even greater tendency to get
back into the input. A good magnetic pickup for audio
frequencies is the primary of a small mains transformer with the
core removed, connected instead of the normal input coupling
coil. The demodulator will be fairly ineffective at audio
frequencies and if you want to remove any demodulation effect,
you could remove C6. If you wanted the AM demodulator to work
down to lower frequencies you may need to increase the value of
C6.
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© Henry J. Walmsley 2014
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Recent Edit History
19-APR-2026: some formatting