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

Shortwave Coil Windings for TRF RadioSW
            Coil for TRF Radio

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