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I am in 12th std, the reason why I am mentioning this is that we are given a PROJECT to do in Physics subject. And then one day I searched the internet and found this amazing thing called 'Crystal Radio'. And when I showed it to my group(since it is a group project), their faces were like WTF??? Because the crystal radio works only on the energy of radio waves and no external power source!!! And my friends then started to ask me that how can this be possible... Then we went to our Physics teacher and he said that he made a crystal radio when he was in 11th and it didn't worked for him since the energy produced by the receiver is very small... I didn't knew what to answer to my friends then... So my short and simple question is that "Does the Crystal Radio really works??" And if yes then can you please provide the link to where can I find the working mechanism of a crystal radio... Thank You!!

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  • $\begingroup$ Given what you learned about crystal radios when you did some basic research (like, searched for "crystal radio" on Google), do you really think it's a hoax? Surely you saw the second sentence of the Wikipedia article: "It needs no battery or power source and runs on the power received from radio waves by a long wire antenna." $\endgroup$ – Phil Frost - W8II Dec 26 '13 at 15:24
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Yes, crystal radios convert radio signals to audio without any additional power.

But it is true that there is not much energy in a radio signal at any significant distance from the station, so a few tricks are involved to produce audio from that weak signal without any additional electricity:

  1. The earphones are special models that are high impedance and require very little current to operate. Modern earbuds like you use with a mp3 player or cellphone have a low impedance and will not work.
  2. These earphones are connected as the load to a high Q resonant circuit, which collects and concentrates energy at the desired radio frequency.
  3. AM radio in particular can be decoded to audio with a diode or crystal. Other more modern modulation types (FM, Digital Audio) can not be decoded in this way.

Getting a crystal radio to work depends upon having some strong local stations, a good antenna AND ground, and not having a good ground will keep it from working. If you have copper plumbing, attaching to the cold water service can be a good ground if the water service arrives from the ground without any plastic PVC pipes.

Here are some links which may give you a fuller understanding:

http://en.wikipedia.org/wiki/Crystal_radio

http://scitoys.com/scitoys/scitoys/radio/radio.html#crystal

http://www.crystalradio.us/

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  • $\begingroup$ So do you mean I need to use the 'Piezoelectric Earphone' or what is called the 'Crystal Earphone'? $\endgroup$ – radiantshaw Dec 23 '13 at 8:37
  • $\begingroup$ Yes, and a crystal earphone and piezoelectric earphone are likely the same thing. $\endgroup$ – Paul Dec 23 '13 at 19:44

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