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-boun...@febo.com [mailto:time-nuts-
boun...@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@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@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@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
