[time-nuts] What is the best counter for a Time Nuts?

Ulrich Bangert df6jb at ulrich-bangert.de
Thu Oct 9 08:58:18 UTC 2008


Gentlemen,

first of all I would like to thank you for your feedback. 

Reading in the literature that some of you supplied revealed that modern
counters may work even more tricky than i had though but that their
"tricky output" is NOT easily taken as the input for AD computations
without additional precautions.

> The Ref Output on the front panel of the SR620 is derived 
> (1/10,000) from the 
> EXT IN on the rear panel.  So when you apply a 10 MHz signal 
> to EXT IN you get 
> a 1 kHz REF OUT.  Appendix B in the PSR10 Rubidium source 
> manual describes how 
> to use this along with the arming function to average 1,000 
> measurements per 
> second resulting in 2E-12 per second on the display.  i.e. 
> very close to the 
> HP53132A.  So no external hardware is required and no PC to 
> get this result.

After I had read this suggestion of Brooke I immediately gave it a test.
With a reference and a DUT both believed (due to other
experiements/measurements) to be stable < 3E-12 @ 1s I received the
results attached.

And of course you do not get a frequency value as

> second resulting in 2E-12 per second on the display

may indicate. The counter works in time interval mode in this
arrangement and you get 1 s data of delta ts between 0 and 100 ns that
need to be un-wrapped. I would judge that this method is well suited if
a DUT needs to be trimmed to 10 NHz with high resolution but I fear that
it does not help us in high stability measurements since the intrinsic
noise is still more than a decade too high.

Best regards
Ulrich Bangert

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Brooke Clarke
> Gesendet: Mittwoch, 8. Oktober 2008 23:43
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] What is the best counter for a Time Nuts?
> 
> 
> Hi Bruce:
> 
> The Ref Output on the front panel of the SR620 is derived 
> (1/10,000) from the 
> EXT IN on the rear panel.  So when you apply a 10 MHz signal 
> to EXT IN you get 
> a 1 kHz REF OUT.  Appendix B in the PSR10 Rubidium source 
> manual describes how 
> to use this along with the arming function to average 1,000 
> measurements per 
> second resulting in 2E-12 per second on the display.  i.e. 
> very close to the 
> HP53132A.  So no external hardware is required and no PC to 
> get this result.
> 
> Have Fun,
> 
> Brooke Clarke
> http://www.prc68.com
> http://www.precisionclock.com
> 
> 
> Bruce Griffiths wrote:
> .....
> > 
> > It is also possible to use a SR620 or a 5370 to take 1000 
> > timestamps/sec. However may require using some external hardware 
> > (frequency divider). For maximum accuracy and precision the 
> resultant 
> > data has to be logged and processed off line using a PC or other 
> > computer.
> > 
> 
> 
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