[time-nuts] HP5370B anomaly

[Bruce Griffiths]

Magnus Danielson wrote:
> 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.
Why?
What about a periodic effect due to crosstalk at the interpolator mixer 
FFs inputs?
>
> 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.
You suspect the LED drive signal?
>
> It would be nice if others would see if they could achieve the same 
> effect.
>
> Cheers,
> Magnus
>
>

What is the amplitude of the effect?
How good a source pair is required to see it?

Bruce