[time-nuts] HP 5370B jitter

Ulrich Bangert df6jb at ulrich-bangert.de
Sat Jul 14 05:14:16 EDT 2007


I few years ago I bought an HP5370A about the seller was saying that he
was selling it that cheap (200 US$) because he was not able to test
whether this device would hold its specifications.

As it turned it displayed SOMETIMES large amounts (a few hundred
picoseconds) of RMS jitter and NOT on other times on the handbook's
jitter self test. I have been trying a lot to improve the situation by 

a) correctly adjusting the input trigger circuits

b) correctly adjusting the 200 MHz multiplier

c) correctly adjusting the two interpolator boards

Each of the adjustment procedures went exactly as descibed in the
handbook. However, there was no improvement on the total situation. The
counter insisted on sometimes behaving this way and sometimes the other
way. Sometimes it seemed as if there were even a slow continouos
movement between the two extremes perhaps due to temperature. I had
already realized that the counter was scrap with no sale value when I
remembered my friend Frank who happens to repair old HP stuff for one of
the local surplus dealers. He had an defective 5370A around so that I
was able to make some exchanges on board level. 

After changing some boards forward and back it became appearant that
exchanging ONE of the interpolator boards would immediatly change the
situation in that way that the counter would display an RMS jitter of
30-40 ps for any amount of time I would give him. So clearly the this
interpolator board had an problem. Most of the electronic stuff on the
interpolator board is plain electronics that might been gathered even
today with the BIG exception of the oscillators that are part of the
phase startable plls on the interpolator boards. These oscillators are
of the delay line type and are contained in the unusual looking metal
cans on the interpolator boards. So I had to test, whether the problem
was located in this oscillator (in which case I was in difficulty
because it it a HP propiarity product) or elsewhere (in which case I
would be probably able to repair the board).

By exchanging the oscillator between the boards the problem wandered, so
clearly the problem WAS in the oscillator. Fortunately enough I managed
to coax Frank a "bad" interpolator board with a good oscillator and
since that my 5370 works ok.

Best regads
Ulrich Bangert      

> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Didier Juges
> Gesendet: Samstag, 14. Juli 2007 05:38
> An: 'Discussion of precise time and frequency measurement'
> Betreff: Re: [time-nuts] HP 5370B jitter
> ); SAEximRunCond expanded to false
> Errors-To: 
> time-nuts-bounces+df6jb=ulrich-bangert.de+df6jb=ulrich-bangert
> .de at febo.com
> Magnus,
> 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 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
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