And, perhaps the OCXO contributes quite a bit, too.
I don't think the cheap X-tal oscillators in the small boxes are as good
as a 10811A in terms of phase noise etc...
Also, the buffer amps might be not as good as the 5065A ones. At least I
remember having observed significant frequency changes caused by load
changes.
After some 1 1/2 years of continous operation of my 5065A, I could't
measure any difference to my 5061A, even after averaging over 1 hour of
counter readings.
The FRK however suffered from massive runaway after plugging it in the
counter...
Adrian
John Miles schrieb:
-----Original Message-----
From: [email protected] [mailto:[email protected]]on
Behalf Of Bob Voelker
Sent: Sunday, March 21, 2010 1:59 PM
To: [email protected]
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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