Picking up a radio station

[Britt34]

Hello. I am currently in school for EET. I like to go online and find circuits to build with my xk-700 trainer kit. The other day I built the Buzzit circuit which is suppose to make different alarm type sounds. So I built the circuit and somehow it didn't do what it should. However I picked up a radio station and was able to change it with the potentiometer (spelling). I took it apart and now when I try it again, I cant find how I did that. Would anyone know what I did. HEre were the active components. 1M variable resistor or potentiometer, 33K, 1K, pnp and npn transistor, 100n capacitor and speaker.

 

[MikeMl]

An "AM crystal radio" is just an antenna and tuned circuit followed by a diode rectifier optionally followed by an audio amplifier. If you are close to an AM transmitter, you don't even need a tuned circuit; any wiring that the signal can be induced into will work as the antenna. Any semiconductor device will work as the rectifier, as will a galena crystal and sharp-pointed thingy, or a safety-in and blued razor blade. If there is any amplification in the audible range and an earphone/speaker, then you will hear it....

 

[Hero999]

I'd recommend the following circuit.

Wikipedia says it's impractical but this can be solved by making the inductor variable which is exactly what I recommend.

Crystal radio - Wikipedia, the free encyclopedia