AmateurRadio.com

Before this blog I had a web site with some amateur radio information.  It is still out there, but I should close it down or update it totally.  Here is one of the projects from those pages which I had great fun with and which is worth adding to this blog.  I was quite impressed with the quality of the audio from this receiver which has just seven components (three capacitors, two transistors, a resistor and a transformer).  Below is an edit of what was originally written a few years ago.

I constructed this simple receiver having seen the circuit at WB4LFH’s web site which he calls the ‘audion’. This circuit is almost identical to the last circuit on that page, except I changed the inductor connection to the variable capacitor from being a tapped connection to being a transformer coupling.

The inductor was a T50-2 toroid with secondary being 28 turns of enameled copper wire and the primary (connected to the antenna) being two turns. (Remember a ‘turn’ on a toroid is the passing of the wire through the hole). The transistors were 2N3904 types, but you can try any general npn transistor. The tuning capacitor was a air plate type taken from an old radio receiver, likely about 300pF. The circuit was constructed ‘ugly style’ on a small piece of unetched circuit board. Use what you have in your junk box and experiment.

The performance is very good considering the simplicity of this receiver. Below are a set of sound recordings from this receiver.  The recordings show how the volume can change (no AGC here!) and that the selectivity is not too good.

• Guitar music
• Station identifier
• Radio Habana Cuba

If you consider building this receiver please note that these recordings were done with the receiver connected to my external antenna at that time, a G5RV. I tried using a long whip antenna, which I had in the junk box, and there was no discernable reception of a signal with it. So you will likely need to use a good length of wire to act as an antenna. Post a comment if you have any success with this circuit.