[time-nuts] Cesium C Field Set?
Brooke Clarke
brooke at pacific.net
Fri Feb 11 19:50:58 EST 2005
Hi John:
Well if your talking digits to the right of 1 then the SR620 has 12
digits, i.e. the LSD is 1 pico second.
There's a procedure in appendix B of the PRS10 Rubidium Source manual
that allows making a time interval measurement on very stable sources to
parts in E-12 in one second. This is done by using the 10 MHz standard
and reference signals as the start and stop inputs to a time interval
measurement and then adding a 1 kHz external trigger arming input and
averaging 1,000 measurements each second. The result is a time interval
measurement accurate to 1 pico second every second.
Have Fun,
Brooke
PS It's been about 8 hours since I changed the GPS settings to 4 highest
and the elevation mask to 30 degrees and so far the peak to peak
wandering has been about 50 ns. Much better than before, but time will
tell.
PPS I have the 2100T set for 3200 GRIs time constant. The manual
indicates that this is desirable for stable sources. The stability is
now showing E13 4.9 and the absolute time difference is -0.03 micro
seconds But 0.03E-6 / (3200 * .099400) = 9.43E-11 not 4.9E-13 so I
still do not know how the 2100x receivers are calculating the stability.
John Ackermann N8UR wrote:
> Bill Hawkins wrote:
>
>> We could get a little more quantitative about "impact" because there is
>> a relationship between the number of digits displayed and the number of
>> digits of accuracy. If you have an eight digit interval counter then
>> 10e-9 is enough accuracy. You can do that with the crystal in some
>> counters if it has been calibrated, but your external standard certainly
>> has enough accuracy.
>>
>>
>
> Good point, but my 5370 counter has 11 digits of time resolution (as,
> I think, does Brooke's SR620), so the exponents start to get pretty
> small...
>
> John
>
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