Re: Tunnel diode rectification

From: Watson A.Name - \ (NOSPAM_at_dslextreme.com)
Date: 03/10/05 

Date: Wed, 9 Mar 2005 22:15:23 -0800

"Theo Markettos" <theom+news@chiark.greenend.org.uk> wrote in message
news:oux*Rw8Iq@news.chiark.greenend.org.uk...
> Fred Abse <excretatauris@cerebrumconfus.it> wrote:
> > On Mon, 07 Mar 2005 16:31:25 +0000, Theo Markettos wrote:
> > The valley floor has to be above zero, otherwise the device would
contain
> > a voltage source.
>
> True, good point.
>
> > "Reverse breakdown" isn't really a property of tunnel diodes, they
conduct
> > in the reverse direction more or less from zero.
> >
> > Tunnel diodes don't rectify, in the sense that I take you to mean
the
> > term.
>
> Am I misreading something from the graph at:
> http://www.americanmicrosemi.com/tutorials/tunneldiode.htm
>
> which seems to suggest that they're basically like a Zener except the
> tunnelling current means they have a lower resistance at low applied
> voltages than at medium ones? I suppose the problem is lack of scale
on the
> left/lower parts of the graph. It does seem to suggest that they're
> actually better at conducting in the reverse direction than the
forward
> direction - is this true? I can't seem to find any datasheets on
these
> diodes.
>
> My interest is for a crystal radio, where the forward voltage drop of
a
> silicon, Schottky or germanium diode means you lose a lot of signal,
but
> power isn't available. I was wondering whether a tunnel diode might
be more
> efficient? Are there any other types of diode that might do the trick
> instead?
>
> Thanks
> Theo
>
> --

You're supposed to do it like this.
http://www.oldradioworld.de/gollum/dt.htm

These use a separate diode to rectify and filter the RF, then power the
amplifier with it. So you are getting free power from the RF in the
air. Just remember to use a long wire, the longer the better.
Germanium diodes will rectify with a drop of only a quarter volt.

Or you can use a solar cell that puts out a few volts to furnish the
power to amplify the RF and/or AF. You can also buy one of the radios
that has a solar cell and crank built in, and will run off the crank
generator for several minutes or off the solar cells if it's sunny.

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