[time-nuts] HP 5370B jitter

Didier Juges didier at cox.net
Fri Jul 13 23:37:58 EDT 2007


My first 5370A had severe distortion on the 10 MHz output, but in my case.
It looked like 30 MHz with some 10 MHz component (no 5 MHz), and was
otherwise stable. It turned out some of the capacitors in the output filter
of the amplifier board had cold solder joints (not unusual on these units),
causing the tank circuit to resonate at 30 MHz instead of 10. Once reflowed,
all went back to normal (except that did not fix the bad socket problem, but
that's another issue :-)

Didier KO4BB

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Magnus Danielson
Sent: Friday, July 13, 2007 4:04 PM
To: time-nuts at febo.com
Subject: [time-nuts] HP 5370B jitter

Hi fellow time-nuts!

As my vacation started this evening, I spent some time in the lab (at work,
since that's where I find my Wavecrest and it has better selection of active
probes), trimming up the 200 MHz multiplier chain. I shifted it down from
17 ps RMS to 3.9-4.0 ps RMS. Most of the trimmings where on the 200 MHz part
where as the 50 MHz part where fairly clean already from start.

I may be able to tweak the jitter of the 200 MHz down further, but it would
require more work than my rather quick-and-dirty approach.

However, I was quite supprised to notice that there is alot of modulation on
the 10 MHz output. The histogram shows two distinct gaussian bells and when
checking the high-frequency modulation it showed a 5 MHz modulation. The
spectrum analyzer clearly shows the 5 MHz output.

I will make more investigation to the source of that 5 MHz, but it is
If it is a property that my 5370B shares with others, then it will certainly
a limiting factor for self-referenced jitter measures as well as use of the
output for low-jitter measures.

I think the main source of sub-10 MHz clocks is the divide down on the CPU
board A9. It generates control signals which is sent along the motherboard
there is alot of chance to jump over and infect the output buffer.

Could you please have a look with a spectrum analyzer on your 10 MHz output.
I have not checked how it behaves with external 10 MHz applied.


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