[time-nuts] 5370B arrived - any FAQ

wje wje at quackers.net
Thu Jun 19 07:53:02 EDT 2008

Congratulations! It's a wonderful instrument, isn't it?
I can answer a few of your questions.

Set/clear ref - after power-on or a reset, the ref value is (should be) 
When set-ref is pressed, the current time interval average value is 
stored. This remains set until a power-off/reset or you clear it. The 
buttons don't light up.

Freq vs time interval - simplistic answer: when you're using 
time-gating, you're looking at more samples than in averaged one-period 
mode. For 10Mhz, a gate of 0.1 secs is 1 million periods. In period 
mode, you're averaging a maximum of 100,000 periods. Accuracy is 
proportional to the square root of the number of samples.

The 'specifications' section of the manual gives the formulas for 
determining both resolution and accuracy (which are NOT the same) for 
the various modes.

I would suggest you go through the detailed alignment procedures even 
though the unit passes the operational checks. These units almost always 
have drifted out of alignment in the analog front-end unless you were 
lucky enough to get a freshly-calibrated one. You can usually 
significantly improve channel-to-channel trigger consistency and lower 
the jitter by doing so. It's a tedious process, and some of the pots are 
virtually impossible to reach, as are some of the test points, but it's 
worth the pain. The theoretical one-sample measurement accuracy is 20ps, 
but a non-adjusted unit can add many tens of ps of jitter. HP states a 
typical jitter of 35ps; with very careful tweaking, you can get better 
than that; mine reports 21-23 ps averaged over 1000 samples. (I'm not 
entirely sure I believe that, though)

Bill Ezell
They said 'Windows or better'
so I used Linux.

Jim Palfreyman wrote:
> Hi Folks,
> Well my 5370B purchased off ebay arrived from the US in perfect
> condition. It passed all the operator checks (all well within spec)
> and the only issue being that the internal 10811 oscillator was
> running a tad slow. A quarter of a turn with the screwdriver fixed
> that.
> Having played with it for a day or so I have a few questions. I was
> wondering if there was an FAQ anywhere?
> My first issue was powering it up. It said on the socket on the back
> 110-240V and I nearly just plugged it in out of habit (as you can do
> with modern power supplies). I decided to read the manual, however and
> was so glad I did. 240V into it without flipping the little board over
> and changing the fuse would have been a disaster! I didn't have a 1.25
> amp fuse but a 1 amp worked ok.
> Second issue was opening the cover! It wasn't in the manual and I
> couldn't find it anywhere on the net. I figured it out in the end
> (undo the screw at top rear and remove the top two feet and slide the
> top back). My top didn't slide easily and so it wasn't obvious.
> My third issue I'm not sure how it happened and I think it was a bug.
> After lots of prior fiddling I started taking measurements between two
> 1 PPS readings from two different GPSDOs (Thunderbolt and Z3815A) and
> it was telling me the difference was 980 nsec. Checking the waveforms
> on an oscilloscope said it should have been of the order of 3 nsec.
> This had me stumped for ages until I clicked the DSP REF button and it
> showed -977! This was obviously from previous fiddling but I thought
> the SET REF button would be lit if REFERENCE was non zero. I haven't
> been able to repeat this. Any ideas? Motto here is always click CLR
> REF to be sure.
> Another thing I don't understand is to do with frequency measurements.
> Gating with 0.01, 0.1 or 1 second gives good results for a reference
> 10 MHz, but why does measuring the same frequency with the 1 PERIOD
> set and say 1000 samples not give good results?
> Thanks in advance,
> Jim
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