[time-nuts] another Ebay mixup, 5370

John Miles jmiles at pop.net
Sat Jun 9 17:02:29 EDT 2007

Note that while the resolution spec is 20 ps, HP's jitter spec is 100 ps, so
anything under that is fair game.  I will confess that I have never
understood how it's meaningful to specify a single-shot resolution figure
that is 5x better than the instrument's specified jitter.

10-15 ps is about what I get with mine (10 MHz from TBolt driving both the
external-ref and START jacks from separate ports of a 5087A distribution
amp).  The mode in this case is TI, STD DEV, 1K samples, +/- TI arming.

This 5370B is quieter than the others I've seen.  20-30 ps is more common
for this particular test.  I've never seen one worse than 50-60 ps, though.

Make sure that the TRIG LVL readouts are in tolerance (approx. +/- 2 V at
the limits, and within +/- 0.01V of 0V in PRESET).

To get very far in the calibration process, you need an HP 8082A triggerable
pulse generator.  Without an 8082A, you can bluff your way through the front
end adjustments and DAC level settings (beware misprints in the manual
there), but if you try to adjust the interpolator, you will find that you
have no way to tell what's going on.

I have an 8082A now, but I didn't own it the last time I was under the hood
of this 5370B, so I have no idea how well-calibrated my interpolator's
anticoincidence circuit is.  It probably isn't, considering that I got
halfway through the calibration, realized that no, they're not kidding, you
really DO need an 8082A, and tried to put the trimmers back somewhere close
to what I remembered seeing before I messed with them.

I suspect this has been the fate of pretty much every 5370 out there, which
could account for some of the phase slips and other anomalies people
sometimes observe in long-term tests.

-- john, KE5FX

> this was the recommended setup (by HP) for checking the internal
> noise. Feed
> the 10MHz output back to the input using a short cable, and set
> the  unit for
> "COMMON" input, setting 50 Ohm impedance etc.
> In the meantime I did some more tests, and found the following:
>    1) The sine-wave output is crappy. The sine wave has some sort  of
> "Class-B" cross-over distortion, and it measures a whooping 200ps
> RMS jitter  on my
> Wavecrest jitter analyzer (>400ps pk-pk). Compare that to 2.7ps
> RMS  jitter I
> measure on our Fury 10MHz output. Definitely the crystal got damaged,  or
> something else.
> The unit has about 2x better jitter performance (around 50ps RMS)
> if I feed
> a clean Fury 10MHz into it. I think the 10811 OCXO or the
> internal driver
> circuit may have gotten damaged.
>    2) As described earlier, with the Fury GPSDO driving the  unit's ref
> input, and very careful adjustment of the trigger level I can get
> RMS  readings
> <30ps with good time-intervall output. This is on a setup as  follows:
>    REF-IN driven by Fury unit A 10 MHz output
>    One input driven by second Fury unit B 10MHz output
>    Second input driven by PRS10 GPSDO 10MHz output
>    Unit set to measure +-Time Intervall
> I am happy with that result, except the trigger pot sensitivity,
> it's very
> hard to set correctly, and sometimes jumps to >60ps RMS by
> itself. I hope to
> be able to replace the 10811 - although feeding it externally is
> not a bad
> idea,  and hopefully get the full <30ps performance in "preset"
> mode after full
> calibration.
> Has anyone had similar problems?

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