[time-nuts] Measuring 10 MHz accurately.

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed May 7 20:30:47 EDT 2008

Brooke Clarke wrote:
> Hi Ulrich:
> The SR620 has a 1 kHz Reference output that's derived from the 10 MHz external 
> clock input.  It also has a Gate/Arm function.
> Appendix B in the PRS10 Manual explains how to use these two features to make 
> 1,000 time interval measurements per second thus averaging the 20 ps one shot 
> way down.  http://www.prc68.com/I/PRS10.shtml
> The time interval armed 1,000 times per second and the difference between zero 
> crossings of a pair of 10 MHz signals are measured.  So the range of 
> measurement is 100 ns before rollover.  I think at least one of the test 
> signals needs to be 10 MHz to drive the external clock input to get the 1 kHz 
> reference.  But you could use Toms PIC divider to generate a 1 kHz signal from 
> about any test signal and use the same method.
> http://www.prc68.com/I/FTS4060.shtml#SR620Fast
> http://www.prc68.com/I/TandFTE.shtml#SR620
> Have Fun,
> Brooke Clarke

What about the effect of the phase modulation of the 1kHz output by the 
100Hz, 10Hz, 1Hz outputs due to simultaneous switching effects from such 


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