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charles c. johnson
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Has anyone here made a crystal radio.  Need help getting started with junk radios

here is a link  http://en.wikipedia.org/wiki/Crystal_radio

doesn't need batteries
 
                                
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Yup. They were all the rage back in the day. Only picks up AM tho, bummer. Way better than nothing in an emergency.
 
ronie dee
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I used a Germanium diode. Don't have a clue where you can get one.
 
                                
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Diode's a diode. As long as it's a signal diode and not a power diode. We used Galena crystals back in the 50's with a short piece of banjo string, the latest in hi-tech, lol.
 
ronie dee
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I made a copper coil around a tube and had a copper arm that moved along the copper winding. I could change stations. I thought the germanium diode was the power source. But i really never understood it. My dad helped me build it in the 50's...I would check it now and then to see if it still worked... It always did. Lost track of it in the 80's.

 
                                
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The diode only serves to rectify or "detect" the signal. The Power source is the radio waves them selves which is why the sound will not be too loud unless you add an amplifier stage. BUT...then you gotta have batteries, it never ends, lol.
 
ronie dee
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Yes, I had to have a headset to listen to the radio. Maybe one could use a large cone like the old phonographs had to amplify the sound a little.
 
Joel Hollingsworth
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Location: Oakland, CA
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rockguy wrote:
The diode only serves to rectify or "detect" the signal. The Power source is the radio waves them selves which is why the sound will not be too loud unless you add an amplifier stage. BUT...then you gotta have batteries, it never ends, lol.


Hear, hear. The power source is the transmitter station; sometimes, they'll mention how much energy they use to generate the radio signal, sometimes up to 50,000 watts.

Another way of thinking about the diode is that it accumulates the signal. The radio waves draw electric charge back and forth through all the wires in your radio hundreds of thousands of times per second. The diode skims some energy out of each cycle, so that enough builds up to push on the speaker membrane. But the amplitude of the radio signal changes all the time, pushing the speaker membrane more, and then less.
 
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