[time-nuts] HP 10811 Tuning Diode

[Tom Curlee]

I'll second the interesting part. 

I have a problem with a 10 GHz brick oscillator LO that I converted to GPS lock.  I don't remember the instantaneous frequency jumps (around 200 - 400 HZ at 10 GHz) before I did the GPS lock (although it's possible).  Please note that this is NOT any type of GPS phase shift.  I built a extremely slow frequency lock circuit that has a loop time in seconds.  The jump is instantaneous and I can then see the control voltage slowly change to correct the error.  When the frequency jumps back, the control voltage slowly follows.  Since this brick has the usual 106.5 MHz crystal (multiplied by 96 to get 10.224 GHz for the LO), I'm seeing at most 400 HZ / 96 shift in the crystal oscillator.

I've wondered if I have a noisy varactor diode.  The diode selected was one I had around, selected only because it had a low-ish capacitance value.  I haven't gotten around to digging into the problem any farther.

Anyone have any more info or ideas?

73,

Tom  WB6UZZ

--- On Thu, 10/18/12, John Miles <jmiles at pop.net> wrote:

From: John Miles <jmiles at pop.net>
Subject: Re: [time-nuts] HP 10811 Tuning Diode
To: "'Discussion of precise time and frequency measurement'" <time-nuts at febo.com>
Date: Thursday, October 18, 2012, 8:54 PM

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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