As a child I'd made a crystal radio set and had been meaning to make one again when I came across stories of foxhole or PoW radios made from scavenged parts. These were made during the Second World War (and other wars) from copper wire from a broken motor or alternator and anything from which a diode could be fashioned.
So, I decided to give it a go. Here's my foxhole radio. It's made from: a toilet roll tube, some copper wire, a blue steel razor blade, the tip of a pencil, a piece of coat hanger and an earpiece. Connected to ground and a long wire antenna in the garden it works... just. (PoW's seem to have used the barbed wire of the prisons they were held in as antennas, I used a long piece of bell wire).
1. A coil of enameled copper wire wound about 100 times around a toilet roll tube. I used 22 SWG wire.
3. A crystal earpiece.
4. A diode made from a blued steel razor blade, the point of a pencil and a safety pin. I bought a blued steel antique razor blade on eBay after having trouble with the modern blade that I blued myself.
Modern blade blued on the gas stove (I just held it with pliers in the flame until it turned blue which took just seconds).
Here's the end of a pencil and safety pin combination:
The circuit is essentially the same as this classic design with my razor blade/pencil combination instead of the cat's whisker detector in the picture.
point contact diode which is able to detect the AM radio signal.
There are three radio stations that I can hear using the set, the loudest one appears to be Sunrise Radio an AM station catering to London's Asian community. Here's a recording of a few seconds of reception using my radio (it's very quiet, turn your volume right up): MP3.
There are lots of improvements that could be made. Currently, there's no capacitor in the circuit and so it is relying on capacitance in the antenna to make a tuned circuit. Fashioning a capacitor from aluminum foil and newspaper would probably help.