[time-nuts] HP 5065A performance vs. others

John Miles jmiles at pop.net
Sun Mar 21 22:58:40 UTC 2010


> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Bob Voelker
> Sent: Sunday, March 21, 2010 1:59 PM
> To: time-nuts at febo.com
> Subject: [time-nuts] HP 5065A performance vs. others
>
>
> As several postings have indicated, the performance of the HP
> 5065A is better
> than many of the other rubidium standards.  What enables the HP 5065A to
> achieve better performance?--Is it the physics package or the particular
> control system implemented in electronics?  Would it be possible to
> achieve the HP 5065A's performance by modifying a more commonly
> available rubidium such as the LPRO?  Would an ensemble of LPROs
> match a single HP 5065A in performance?
>
> Bob


I think those are all open questions, because it's not immediately clear
what limits the performance of the smaller telecom-grade physics packages,
or what low-hanging fruit might be left on the tree.

For instance, how important is the length of the path the light takes
through the filter cell and/or resonance cell?  It's obviously a lot longer
in a 5065A.  Or is it HP's proprietary buffer-gas mixture that makes most of
the difference?  Is there something special about HP's lamp?  Is their
microwave synthesizer that much better?

HP's temperature stabilization is better than the LPro's -- so maybe it
would help if you just moved the LPro's Rb assembly into an outer oven,
separate from the rest of the electronics.  How important is all that
mu-metal shielding on the 5065A, given that most people these days would
care more about stability than absolute accuracy (thanks to GPS)?

Someone with more free time should tackle these questions. :)  F. G. Major's
book would be a good starting point, and this paper on laser-pumped Rb
clocks also has a lot of hints about what limits the performance of ordinary
sources: http://tf.nist.gov/general/pdf/1219.pdf .  They used the cell from
a commercial Rb standard in their experiment, although they didn't say which
one.  If nothing else, you can infer from this paper that the path length
through the resonance cell isn't a huge deal.

-- john, KE5FX




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