[time-nuts] HP 5370B jitter

[Magnus Danielson]

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 annoying.
If it is a property that my 5370B shares with others, then it will certainly be
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 so
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.

Cheers,
Magnus