[time-nuts] HP 10811 Tuning Diode

[Bob Camp]

Hi

The normal 10811 package has several openings in it. Light *might* get in
there. A "micro volts" level of noise can mess up your phase noise if it's
AC noise at a low frequency. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Adrian
Sent: Friday, October 19, 2012 4:10 PM
To: richard at karlquist.com; Discussion of precise time and frequency
measurement
Subject: Re: [time-nuts] HP 10811 Tuning Diode

I didn't notice any damage, nor was there a visibly bad solder joint.
However, I couldn't reproduce the excess noise with a quick bench test 
at 30V / 100k neither.
DC-wise there are a few microvolts only. Same with the SMD diode.
Exept, when the original glass diode is exposed to light. With a LED 
Maglite, I got up to 50 mV (across 100 kOhm) out of it!
But there is no light shining inside of a 10811, is there?

I had first suspected a 0.1 ceramic cap, but that didn't cure the phase 
noise desease.
The diode in the original circuit appeared to be heat sensitive,
and the excess phase noise has gone away since I replaced the diode.
The noise was clearly there, and it was also there using a test adapter 
and two lab power supplies.

Adrian

Rick Karlquist schrieb:
> I wonder if the glass case got a crack in it or if the kovar seal
> was failing.  Maybe a failed solder joint (which gets fixed when you
> install the new diode). I've never heard of a noisy varactor before
either.
>
> Rick
>
>
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