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? > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
