[time-nuts] HP 10811 Tuning Diode

[Adrian]

Rick,

thanks for the hint. I had a 2x 45 pF SOT23 diode at hands that works 
fine. The frequency could be adjusted without any changes to the 
circuit. Now as the 10811 is back in the 8662A, the diode will most 
likely keep living happily in there.

John,

it's a bit tricky. First of all, you need a fast phase noise display 
like the 3048A spot measurement. Otherwise you have no (almost)  
immediate indication of changes and only get the average noise over a 
longer period displayed, which, of course, also indicates that there is 
something wrong.

For intermittent and temperature dependent failures, a little heat plus 
freeze spray can do wonders. I used a SMD hot air soldering tool that 
allows for selective heating.

In this case, the excessive noise was limited to offset frequencies 
below a few kHz. It appeared to be filtered by the crystal. So, there 
wasn't that much circuitry left, mostly the oscillator stage itself, the 
tunig circuit and power supply.

Adrian



John Miles schrieb:
> 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
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-
>> bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>