I recommend you to read and understand the basic theory of crystal radio published on this article: http://www.buildcircuit.com/how-to-make-a-batteryless-crystal-set-radio/
Making a batteryless/powerless radio is a great fun, but there are also some difficulties.
The most difficult part is making an inductor. When I made my crystal set, I simply took out a ferrite rod from a broken radio and wound enamelled copper wire over it. The wire can be from 25SWG to 30SWG. Regarding the number of turns, just wound wire(2 times) covering 90% length of ferrite rod. There is no exact formula for this. Then, simply connect other components as shown in the figure:
You can use either OA47 or 1N34 Germanium diodes for this experiment.
Some important notes:
* You cannot get FM signals with this receiver set.
* You will not hear any signal if you connect a general earphone that you use for walkman or skype.
* The closer you are from an AM station, the better radio signal you receive. If you are in a distance of 2-3 kilometers from the station, you don’t even need a long antenna. When I was a teacher, my college was near to AM radio station, so it was easy to demonstrate a crystal radio without antenna and ground.
* If you do not have a crystal earphone, you can use a general piezo speaker that you can get inside a musical greeting card, like the shown below.
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