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I'm trying to build a simple AM crystal radio, however, I'm not getting any voltage registered when using it. This is the kind that's only powered by the radio waves. The site I was using to design it makes the circuit clear and how the radio works pretty self-explanatory, but I couldn't read their diagram for making a good antenna. Right now I just have a wad of 22 gauge insulated speaker wire I'm holding up really high so I figured I'd ask stackexchange how to make a good antenna.

How can I build a good antenna for a crystal radio? Here's the site http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p014.shtml

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The simplest antenna for a crystal radio is a long wire (say 10m), and up as high as you can get it. On the roof is best if you can get up there. The wire should be stretched out, not rolled up. Outside is best, to avoid signal loss in any metal in the building's structure. Make sure the antenna is attached with insulators at both ends. To make it simple, take your long wire, attach one end with an insulator. Unwind enough of the wire to reach the other end. Attach it there with an insulator as well, but don't cut the wire. Instead, use the remaining wire to connect it to your radio.

I'm not getting any voltage registered

The voltages generated by a crystal are very small indeed, and they are at radio-frequency AC, so they may not show up on a simple voltmeter. You should be able to see the signal with an oscilloscope though.

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  • \$\begingroup\$ A couple of questions: For my next project if I did an amplified radio would that require a smaller antenna? This is getting to be a bit more work than it's worth putting up the line. Right now I have the wire reasonably straight (it was coiled when I go it) but none of the wire is overlapping. It's all insulated but it's on my roof and it touches the gutter twice. Is that ok because the line is still insulated? Also, does a painted gutter pipe going into the ground work for a ground? Or does that work more of as an insulator? \$\endgroup\$ – RadioSchmadio Jul 23 '12 at 2:40
  • \$\begingroup\$ Having the antenna resonant is the best way to build one. There are ways to shorten then like winding the wire around a fiberglass rod, but tuned antennas are always best. \$\endgroup\$ – SDsolar May 21 '17 at 9:42
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The antenna should be a long piece of wire. Longer is better at AM radio frequencies, where the wavelength is hundreds of meters. Coiling up the wire doesn't help; it's better to stretch it out. It also helps to be relatively near an AM broadcasting station (10 or 20 miles). For my first crystal radio, I had a piece of wire I dropped out the second floor window, reaching almost to the ground.

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What sort of headphones are you using? The construction notes have the audio going into an external amplifier, running off a 9V battery.
If you are going for the original "no power supply" setup, the external amplifier is replaced by HighImpedance headphones. This is typically in electronics stores as a "crystal earpiece".

When you have a crystal earpiece installed, can you hear anything ? Static, hiss, crackles are all background noise and help prove the circuit is working.
However, if all you have is total silence, for THIS setup the next thing I would check is: have you scraped ALL the enamel of the wires, at the junctions?

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I made my first crystal radio in the late 1940s. Just for the hell of it I decided to make one again a few days ago. The first answer to the antenna question is entirely correct. Stretch a long wire (at least 10 meters long) out to a tree and tie it with nylon string away from the branches of the tree. Tie the other end with nylon string away from the building and lead the remaining wire down to your set. Don't let the antenna wire touch anything unless it is well insulated.

As for the high impedance earphones. This is also a requirement but they are more expensive than the cheap ear buds. I used a cheap low impedance (about 40 ohms) ear buds with a cheap matching transformer that I got from All Electronics for less than a dollar. Hope this helps. This old guy had lots of fun!

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