[time-nuts] HP 5372A advice

Morris Odell vilgotch at bigpond.net.au
Wed Jan 20 02:48:33 UTC 2016

Hi all,

I recently was fortunate enough to obtain one of these amazing instruments 
but regrettable no copy of the main operating manual. I find myself a bit 
puzzled by some of it's behaviour.

The unit is clean and passes all the self-tests. When I first got it it 
seemed to work very nicely looking at my in-house 10 MHz frequency standard 
which is a Z3815 GPSDO. It needed a new memory back up battery and once I 
replaced it I tried to do the input sensitivity recalibration procedure 
that's required. That procedure  requires the application of a 10 KHz 60 mv 
p-p sine wave and that's when I ran into trouble.

I have found that if I and try to look at low frequency signals with the 
5372A they appear to have enormous levels of variation and appear quite 
erratic. The histogram display just shows peaks all over the place. I have 
tried with 10 KHz from a 3325B and 100 KHz from a 8656B both of which use 
the GPSDO as a reference and they both show enormous variation. It's the 
same whether I use the GPSDO as a ref for the 5372A or it's own internal 
ref.  If I apply 10 MHz and above from either of the two generators all 
looks well but there are occasional glitches. Using the A or B inputs or 
swapping input pods makes no difference. With VHF and UHF frequencies up to 
the 990 MHz limit of the 8656B it seems to work perfectly using the C 
channel of the 5372B.

I thought it might have been something to do with the synthesized nature of 
the 3325 and 8656 so I warmed up the old faithful 200CD at 10 KHz and it 
didn't make any difference although the 200CD would never be as stable as a 
more modern synthesized source locked to the GPS. I haven't tried it yet 
with anything higher in frequency although I do have a 2 GHz non-synthesized 
generator I could set up.

What's going on here? Any ideas? Do I need to change any of the input, 
trigger or arming settings? So far nothing I have tried in the way of 
changing settings makes any difference.

Thanks in anticipation,


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