[time-nuts] Why using HP5370 ext-ref is (maybe) a bad idea
GandalfG8 at aol.com
GandalfG8 at aol.com
Mon Mar 3 09:08:22 EST 2014
What about replacing the 3336 external reference with something like an HP
10811 and checking what difference, if any, that makes?
In a message dated 03/03/2014 13:42:33 GMT Standard Time,
phk at phk.freebsd.dk writes:
In message <C542ADEE-19DD-4DAB-A1BF-FB842C0775FB at rtty.us>, Bob Camp
>The likely answer is that the trigger point must be changing.
Yes that would be my first theory as well.
> The question is whether it's changing because the
>3336 is doing something (small waveform changes) or because the 5370 is
Yes, and obviously there are many experiments that can be performed
to flesh out the details of that:
Changing the 3336 output amplitude.
Exchanging the signals, so the 3336 feeds ext-ref,
and lab-standard feeds start+stop.
Using a different lab-standard.
Measuring opposite polarity etc.
>I would make up / dig up a coax cable that is 8 degrees at 10 MHz.
>Something around 1/2 meter long should do the job.
As I said, I'm not really kitted out for RF work, so my selection
of coax isn't that versatile and I don't have the crimp-tools or
routine to make my own.
>Next step would be some sort of filtering between the 3336 and the 5370.
>That would help rule out harmonics and spurs from the generator as the
>source of the problem.
The 3336 delivers pretty clean output, so I expect a couple of sanity
checks will exonerate it.
Unfortunately my HP33120 does not have an external clock input, so I
can't use that for the experiment. Anybody with a HP3325 or later
HP33* with an external clock input can participate in this game...
But to be honest, I'm not sure how much more work is really warranted
for me, given that I don't think I can tune the 200MHz multipliers
filters much better than they presently are.
The really interesting experiments, in my mind, would be to ditch the
200MHz multiplier and feed 200MHz from a good generator with high
But then again: It is so much easier to just run the HP5370 on the
internal clock and that solve^H^H^H^H^Hhides all the problems.
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
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