[time-nuts] HP 10811 Tuning Diode

Bob Camp lists at rtty.us
Fri Oct 19 12:23:05 UTC 2012


Hi

Varactors are typically biased through very large decoupling resistors. The
amazing part isn't that they get noisy, it's that they ever are quiet :)..
In most circuits if they ever leaked at the rated "max leakage" spec, you
would see all sorts of trouble. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of John Miles
Sent: Thursday, October 18, 2012 11:55 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] HP 10811 Tuning Diode

That's extremely interesting, Adrian.  I've never heard of a noisy varactor,
but then I've never looked for one, either.  It'd be great if some of the
problems that have been blamed on jumping crystals were in fact caused by
the tuning diode.  What steps did you take to rule out the crystal and
narrow down the problem to the diode?  

-- john, KE5FX
Miles Design LLC

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-
> bounces at febo.com] On Behalf Of Adrian
> Sent: Thursday, October 18, 2012 12:19 PM
> To: Discussion of precise time and frequency measurement
> Subject: [time-nuts] HP 10811 Tuning Diode
> 
> Hello,
> 
> I found the 10811 in my 8662A to be quite noisy and was able to trace
> the problem down to the tuning diode.
> Actually, the phase noise started to jump when the oven heated up. As a
> quick solution, I replaced it with a SMD type that I had at hands.
> 
> I would appreciate any hint where to find an original diode (even though
> I could leave it as is).
> 
> As by the manual, the original is a '0122-0244 DIODE-VVC 100PF 5%
> C4/C25-MIN=2 BVR-30V Mfr. 28480'
> Mfr. 28480 is listed as HP, but the diode is marked 'M' for Motorola and
> '0244' and '312'.
> 
> Adrian
> 
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