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Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
A few months back I built an AM crystal radio from garbage I had laying around the house just to see if it could be done. At the time I didn't have a way to record what I heard or get it to SpecLab but now I do so I figured I would do a write up.
I started with the empty spool from some 20awg wire I used in a tesla coil. I wound a coil of 30awg on to the spool and varnished the windings. Once they were dry I sanded 2 strips on either side of the coil 1 to adjust the ground point on the coil (changing its apparent length) the other to tune the radio. The diode is a "foxhole radio" style detector. It is a short length of pencil graphite on the end of a paper clip pressed against some rust on a razor blade.
The whole setup is very sensitive to bumps but still can deliver a somewhat clear signal. I have attached a clip recorded in SpecLab (unfilterd) as well as a photo of the radio and a screen shot from SpecLab.
If any one else has made a similar setup please share. I find the more primitive radios to be the most interesting because they use so little to get the job done. ]1191782546_53_FT0_homeamradio2.wav[/file]
Banned on 02/27/2008 Registered Member #1326
Joined: Sun Feb 17 2008, 11:19PM
Location:
Posts: 49
The closeup picture of the heart is unfortunately missing. ie the rectifying contact and also the tuner contacts. would like to see them.
Nik wrote ...
A few months back I built an AM crystal radio from garbage I had laying around the house just to see if it could be done. At the time I didn't have a way to record what I heard or get it to SpecLab but now I do so I figured I would do a write up.
I started with the empty spool from some 20awg wire I used in a tesla coil. I wound a coil of 30awg on to the spool and varnished the windings. Once they were dry I sanded 2 strips on either side of the coil 1 to adjust the ground point on the coil (changing its apparent length) the other to tune the radio. The diode is a "foxhole radio" style detector. It is a short length of pencil graphite on the end of a paper clip pressed against some rust on a razor blade.
The whole setup is very sensitive to bumps but still can deliver a somewhat clear signal. I have attached a clip recorded in SpecLab (unfilterd) as well as a photo of the radio and a screen shot from SpecLab.
If any one else has made a similar setup please share. I find the more primitive radios to be the most interesting because they use so little to get the job done.
Registered Member #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
Iron Pyrite (fool's gold) can be used in place of the crystal as well. The benefit of that stuff is its widely available at any little science shop or toy store. I have heard its a bit more finicky than some other options though.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
A guy here has built a broadcast band negative resistance oscillator using iron pyrites:
I believe that a small piece of galena - the sulphide ore of lead - was one of the most popular semiconductors in the crystal-and-cat's whisker days of early radio.
Other Ge diodes besides 1N34A that are usually inexpensive on ebay are OA47, OA90 and OA91. Last year I bought ten 1N34A on ebay for £2 - about US$4, and the other common germanium types are are the same order of price.
Remember that even with a basic crystal set you can easily put a bit of DC bias on your diode from a battery, to make it even more sensitive. Schottky diodes perform better than germanium if bias is used, but not generally so well without it. At a pinch, even red LEDs can be made to work OK in a crystal set if you put a bit of bias on em !
Registered Member #1316
Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365
Harry wrote ...
A guy here has built a broadcast band negative resistance oscillator using iron pyrites:
I believe that a small piece of -galena the sulphide ore of lead - was one of the most popular semiconductors in the crystal-and-cat's whisker days of early radio.
Other Ge diodes besides 1N34A that are usually inexpensive on ebay are OA47, OA90 and OA91. Last year I bought ten 1N34A on ebay for £2 - about US$4, and the other common germanium types are are the same order of price.
Remember that even with a basic crystal set you can easily put a bit of DC bias on your diode from a battery, to make it even more sensitive. Schottky diodes perform better than germanium if bias is used, but not generally so well without it. At a pinch, even red LEDs can be made to work OK in a crystal set if you put a bit of bias on em !
You are right about the use of galena. I have a whole book about makeing your own crystal radios.
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Homebrew Crystal radio
