Crystal Radio Questions

[Joe]

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? That is, I would only hook up one antenna coil
at a time, so should I short the ends of the other (unused) antenna coil
together?

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?

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

Thanks.

--- Joe

 

[Jasen Betts]

On 2009-07-20, Joe <none@given.now> 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

 

[default]

On 20 Jul 2009 09:00:04 GMT, Jasen Betts <jasen@xnet.co.nz> 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/crystalplans/xximages/highpowerp1.jpg
http://www.crystalradio.net/crystalplans/xximages/highpowerp2.jpg
http://www.crystalradio.net/crystalplans/xximages/highpowerp3.jpg

Two others
http://www.crystalradio.net/crystalplans/xximages/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.
--

 

[David Eather]

Joe 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? That is, I would only hook up one antenna coil
at a time, so should I short the ends of the other (unused) antenna coil
together?

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?

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

Thanks.

--- Joe

You can use the base to emitter junction of the transistors, with
germanium the pnp transistors were normally the best.

 

[default]

On 20 Jul 2009 09:00:04 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

Sorry Jason - I mistakenly answered the wrong post
--

 

[Tim Wescott]

On Tue, 21 Jul 2009 06:21:30 +1000, David Eather wrote:

Joe 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? That is, I would only hook up one
antenna coil at a time, so should I short the ends of the other
(unused) antenna coil together?

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?

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

Thanks.

--- Joe

You can use the base to emitter junction of the transistors, with
germanium the pnp transistors were normally the best.

Whatever junction you use you want to short the unused pin to the base.

On silicon transistors the C-B junction is much more robust than the B-E
junction; I would expect the same for a germanium transistor.

--
www.wescottdesign.com

 

[Tim Wescott]

On Mon, 20 Jul 2009 00:07:00 -0700, Joe 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? That is, I would only hook up one
antenna coil at a time, so should I short the ends of the other (unused)
antenna coil together?

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?

Answered already, with the opposite of what my intuition would tell me --
but my intuition was developed with silicon transistors; perhaps there's
some magic to germanium that I don't understand. You may want to try
both ways and see what works best and what seems to be robust.

In my limited experience a germanium diode (1N33; I'm not even sure if
it's epitaxial or point-contact) lasts until the first lightning strike
the next county over, then dies. My kid and I were killing them with a
flea-power spark-gap transmitter (a relay made into a buzzer) in the same
room.

Hot-carrier diodes (a fancy name for low-power Schottkeys) work almost as
well as germanium, and are more robust, if you can lay your hands on
them. Silicon diodes work at a severe cost to sensitivity. I always
wanted to try a silicon diode with a biased detector.

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

It won't gain you anything. The whole crystal radio idea is that you're
trying to power the headphones from energy you harvest out of the aether;
you can't think in terms of volts (or amps) alone, but instead in terms
of efficiency. At best a bridge detector could be made to work as well
as, but no better than, a single diode.

--
www.wescottdesign.com

 

[Tom Biasi]

"Joe" <none@given.now> wrote in message
news:none-2007090007000001@dialup-4.231.170.129.dial1.losangeles1.level3.net...

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? That is, I would only hook up one antenna coil
at a time, so should I short the ends of the other (unused) antenna coil
together?

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?

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

Thanks.

--- Joe

Hi Joe,

This is fun to build also, we got many to work.
If you have some strong signals in your area. There is history behind it
also.
http://bizarrelabs.com/foxhole.htm

Tom

 

[David Eather]

Tim Wescott wrote:

On Tue, 21 Jul 2009 06:21:30 +1000, David Eather wrote:

Joe 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? That is, I would only hook up one
antenna coil at a time, so should I short the ends of the other
(unused) antenna coil together?

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?

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

Thanks.

--- Joe
You can use the base to emitter junction of the transistors, with
germanium the pnp transistors were normally the best.

Whatever junction you use you want to short the unused pin to the base.

On silicon transistors the C-B junction is much more robust than the B-E
junction; I would expect the same for a germanium transistor.

"Robust" is not the desired property of a detector diode and you don't
want to short the unused pin to anything. Your post is simply wrong.

 

[Tim Wescott]

On Wed, 22 Jul 2009 09:08:19 +1000, David Eather wrote:

Tim Wescott wrote:
On Tue, 21 Jul 2009 06:21:30 +1000, David Eather wrote:

Joe 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? That is, I would only hook up one
antenna coil at a time, so should I short the ends of the other
(unused) antenna coil together?

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?

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

Thanks.

--- Joe
You can use the base to emitter junction of the transistors, with
germanium the pnp transistors were normally the best.

Whatever junction you use you want to short the unused pin to the base.

On silicon transistors the C-B junction is much more robust than the
B-E junction; I would expect the same for a germanium transistor.


"Robust" is not the desired property of a detector diode and you don't
want to short the unused pin to anything. Your post is simply wrong.

Every germanium diode I have used in a crystal set died as a consequence
of either fairly distant lightning or a fairly near spark gap.

_You_ may not want robust, but _I_ do.

--
www.wescottdesign.com

 

[NT]

On Jul 20, 8:07 am, n...@given.now (Joe) 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?  That is, I would only hook up one antenna coil
at a time, so should I short the ends of the other (unused) antenna coil
together?

the coils will inevitably interact, either way. Best to wind them with
a gap between them as this minimises the coil capacitance, enabling
wider tuning range.

Don't short the unused one, this would kill the inductor's Q.


NT