Crystal Radios (was Re: List spammer ID'd)

From: Dwight Elvey <>
Date: Fri Mar 30 11:58:23 2001

"Steve Robertson" <> wrote:
> >
> > Sure, albeit a less "authentic" one. I've always heard that
> >germanium diodes are better for this (does this have something to do
> >with their forward voltage drop of 0.3V vs. silicon's 0.7V?)
> >the venerable 1N34A.
> >
> > -Dave McGuire
> >
> Yes... A silicon diode will require a stronger signal to overcome the .7
> volt threshold.
> Since we've already violated the purist aspects by using a semiconductor
> diode, you could use a battery to apply a forward bias to the diode. In this
> model, the signal doesn't need to overcome the entire .7 volt forward bias
> voltage and makes a radio that is MUCH more sensitive.

 All should take a look at this site:
He goes quite a bit into the issues of the "diode knee". He
talks quite a bit about matching of impedences. An unbiased
diode has a quite high impedence. Slightly forward biasing
the diode can make a better match since one can tap off the
tank circuit at a better match. One can work backwards from
the head set to the crystal and then to the tank coil.
 There is another type of diode that might even be better.
They are called back-diodes. These are designed with a vary
low zener voltage. The idea is that the zener can have a
much sharper edge than the log based forward diode.
Received on Fri Mar 30 2001 - 11:58:23 BST

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