[time-nuts] Difference between HP 5370A and 5370B

Poul-Henning Kamp phk at phk.freebsd.dk
Sat Apr 16 07:02:51 EDT 2005

In message <42604A91.60407 at pacific.net>, Brooke Clarke writes:
>Hi David:
>There's an appendix in the Stanford Research manual for the PRS10 Rb 
>oscillator that explains how to make 1,000 measurements each second and 
>thus get 1 ps accuracy every second.  It involves using a precision 
>external clock into the SR620 and connecting the Ref Out (1 kHz derived 
>from the internal or Ref oscillator) into the External Gate input.  The 
>Start and Stop signals need to be something like 10 MHz, or probably any 
>frequency at or above 1 kHz.  And the gate is used to enable a 
>measurement 1,000 times per second. 

I do this all the time with my HP5370B.

Recently, after I wrote a GPIO driver for FreeBSD, I have managed
to get it to spit out "binary format" timestamps, so now I can make
it take 5000 measurements per second (with 20ps resolution and about
50ps noise) and get all the readings onto my computer, not just the

I've been playing with doing FFT's of the samples and I belive I
could clearly see the modulation frequency on my old Rb unit,
but I never really found time to play a lot with it.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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