Re: Unstable Gunn oscillator

In article <42b1d5ac$0$1154$5402220f@xxxxxxxxxxxxxxx>, none@xxxxxxxx
says...
> John Miles wrote:
> > Do you have a large capacitor across the Gunn diode's terminals? Large
> > electrolytics can do funny things there, due to the diode's negative-
> > resistance properties. Easy to make an audio oscillator. I'd say try
> > playing with different bypassing schemes, and maybe take the diode out
> > and clean its contacts with ProGold or something like that.
>
> Thanks for the reference to your page.

Looks like you figured out that I left an 'l' off the end :) -- sorry.
It should have been http://www.qsl.net/ke5fx/gunnpll.html .

> There are only about 220uF parallel to the Gunn, but back in the
> powersupply. The negative resistance applies to the microwave only,
> not to the DC I guess.

Like Steve pointed out, that's not correct. Try running your diode from
a variable supply with an ammeter, and watch what happens to the current
as you raise the voltage. Be careful -- you can exceed the diode's
current spec by running it under its rated voltage!

> I'm feeding 7.1V at 750mA or so and get 60mW
> out of it. This particular Gunn doesn't have a mechanical adjustment
> screw, just a varactor. and yet it does 2GHz between 5 and 22V.
> Yes, that scales down to 130kHz/mV.

Yep... add a frequency discriminator and you have a neat parametric amp!

-- jm

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