[time-nuts] Why using HP5370 ext-ref is (maybe) a bad idea

Poul-Henning Kamp phk at phk.freebsd.dk
Mon Mar 3 16:35:00 EST 2014

In message <5314EF87.1020204 at rubidium.dyndns.org>, Magnus Danielson writes:

>Got a HP3325B, HP5370B/C/D but also 5359A and SR535.
>Another approach is to set a rubidium for a *slow* scan over 

Hmm, I have a 5359A as well, I din't consider that as a possible
input source.

Detuning a Rb is obviously feasible, but being able to key in the
phase you want on 0.1deg units is so much more convenient and

>> 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.
>If that is where the issue is.

Well, seeing how the pattern changed after I tuned A21, I'm pretty
certain that a lot of issues are there, but maybe not all.

It would be really interesting if the plot can be displayed in
something approaching real time, so it would become feasible to try
to tune A21 based on this plot, rather than a spectrum analyzer.

Havn't quite figured out how to do that, but using Fast Binary
mode on the 5370 and a 10,000,000.1 Hz signal from the HP3336 
should be able to do it in half a second...

The one sensible idea I have on the 1.2GHz is that it comes from
the BBB.  A run with the original CPU can resolve that.

Absent that the "1.2GHz" signal simply doesn't make any sense, there
are no frequencies that high in the 5370 anywere, it must be aliasing
of a subharmonic somewhere.

>Those with a high quality RF generator could force-feed a 200 MHz into 
>the counter and see if it makes any major difference.

Yes, that would be an interesting experiment.

>BTW, have someone looked at how the 200 MHz is then used? Sure that no 
>"interesting" interaction happens there?

It's squared up to ECL and fed to the digital side of things.

If anybody have a capable HP82xx that might also be an option.

>> 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.
>Yes, but Poul-Henning, we are time-nuts, we dive deep just for the fun 
>of it, to see what we can learn. :D

Yes, but there is so much to learn, and so little 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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