Re: Crystal Radio Questions

On 2009-07-20, Joe <(E-Mail Removed)> wrote:
> I'm winding a coil for a crystal radio. The original plan says to wind
> the antenna coil on top of the tuning coil, whereas another version says
> to wind the antenna coil *adjacent* to the tuning coil, separated by about
> 1/4 inch.
>
> If I wind both versions of the antenna coil on the form, will one winding
> interfere with the other?

yes, they will be coupled inductively.

> That is, I would only hook up one antenna coil at a time ,

in which case the unused coil will basically disappear.

> so should I short the ends of the other (unused) antenna coil
> together?

No, don't do that.

> Another couple of questions. I have a few germanium transistors, about a
> dozen each of NPN and PNP. What connection should I make to use one of
> these as the detector diode - base and emitter or base and collector?

I'm not sure, ideally you want something like an OA47 diode.

> Would a full-wave rectifier setup using four of these as diodes do any good?

probably not. the idea with the detector in a crystal set is to turn
on at the lowest possible voltage and then to present a high resistance
to give maximum sensitivity and to load the tuning coil as little as
possible to keep the 'Q' high. going to bridge configuration doubles
the impedance.

IME crystal sets need a long antenna and a good earth connection.
modern buildings often use platic pipes, which will make finding a
suitable earth harder, you may have to make one yourself.

the earpiece will be another issue, that should be high impedance too,
like a piezo-electric "crystal" earpiece. if you can't find one perhaps
you could use a small piezo speaker - perhaps with 3.3K resistopr in
parallel

On 20 Jul 2009 09:00:04 GMT, Jasen Betts <(E-Mail Removed)> wrote:

>> Would a full-wave rectifier setup using four of these as diodes do any good?

Yes. Built one driving a loudspeaker with usable volume (when I was a
kid). We had these point contact germanium diodes, back then. They
seemed to work the best for sensitivity and power.

The plans for the one I had:
http://www.crystalradio.net/crystalp...ighpowerp1.jpg
http://www.crystalradio.net/crystalp...ighpowerp2.jpg
http://www.crystalradio.net/crystalp...ighpowerp3.jpg

Two others
http://www.crystalradio.net/crystalp...s/fullwave.jpg
http://www.oddmix.com/tech/cr_highperf_crystlset.html

Master list of designs
http://www.crystalradio.net/crystalplans/

There's a lot of folks still building them and there are lots of good
sources on the net, if you care enough to search.
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On 20 Jul 2009 09:00:04 GMT, Jasen Betts <(E-Mail Removed)> wrote:

Sorry Jason - I mistakenly answered the wrong post
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