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
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