[time-nuts] HP5370B anomaly

Magnus Danielson magnus at rubidium.dyndns.org
Mon Dec 27 04:32:47 UTC 2010


On 12/27/2010 05:01 AM, Bruce Griffiths wrote:
> Magnus Danielson wrote:
>> Fellow Time-nuts,
>>
>> When measuring a pair of OSA 8600 oscillators with a HP5370B I see an
>> oscillating behaviour. It's a stable variation of about 5,5 s.
>> I have tried different settings but no luck. I've used the PPS as
>> start and as External Arming. Very stable pattern.
>>
>> None of the other counters show the same pattern for the same signal
>> sources,
>>
>> Have any other time-nut any good idea what it is?
>>
>> Cheers,
>> Magnus
>>
> Is it present when one 8600 is measured against itself?
> ie use one 8600 to drive both start and stop inputs with PPS derived
> from it as the external arm input.
>
> If not present in this case then the effect may be due to a periodic
> linearity error in the 5370B.

Considering that:

1) I've measured the same signals on similar or higher performance 
counters and not seen it with those units.

2) The frequency difference is so low that I do not experience a 
phase-wrap for the 2476 s long measurement run.

3) The phase slope is much lower than the amplitude of the oscillation, 
so the linearity error can be ruled out completely.

4) The amplitude is stable and does not change with the slope.

5) The unit does not have the 5 MHz noise as I disabled that "feature".

I do howver realize that the START and STOP channels blinks at a fairly 
high rate. These LEDs are driven with signals coming from the A22 board, 
where all the critical timing also passes by... will try to figure out a 
way to handle it, but right now it severely degrades the performance of 
my HP5370B.

I think I discovered the effect at least, with a suspect mechanism for it.

It would be nice if others would see if they could achieve the same effect.

Cheers,
Magnus



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