[time-nuts] Counter Internal Oscillator Importance with External Reference?
Poul-Henning Kamp
phk at phk.freebsd.dk
Tue May 9 13:55:39 UTC 2017
--------
In message <54ee7bdd-0a49-cc49-540d-2812e70dd4f3 at rubidium.dyndns.org>, Magnus Danielson writes:
>Wither it is proper side bands or other systematic noise, it is bad
>indeed, [...]
It's more subtle than that, it can be things like thresholds in
the counters trigger being sensitive to the phase of the internal
clock because of (very slight) cross-talk.
I reported data on this a couple of years ago, as I recall my setup
were something like this:
House-10MHz --> HP3336C clk-in and HP5370B clk-in.
HP3336C output -> HP5370B start then 3m coax then HP5370B stop.
Measure TI(start->stop), for different settings of output phase angle on the HP3336C.
Theoretically that plot should be a flat line.
In practice it is not even close.
I think I convinced myself that the majority of the problem was trigger-noise the HP5370B,
but my notes are not accessible at this time.
--
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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