[time-nuts] How Rubidiums make their frequency
Poul-Henning Kamp
phk at phk.freebsd.dk
Wed Apr 19 16:00:11 EDT 2006
In message <ad9f78230604191255m6deb020arf3bb3b583d385782 at mail.gmail.com>, "Matt
Ettus" writes:
>Since we can now make DDS's with arbitrary frequency resolution, could
>you make an Rb oscillator without the magnetic field adjustment?
>Wouldn't that reduce a source of error in frequency? Then we'd be
>left with the ideal resonance frequency, right?
>
>Are there any other influences on the resonance frequency? I assume
>temperature and density don't matter.
In fact density/pressure does matter and is one of the major reasons
why rubidiums drift: Rubidium is absorbed into the glas container
and as the pressure drops the frequency pulls. The absorption
also makes the glas darker and darker, being a major wear-out
mechanism for Rb units.
As far as I know, this is why Rb is never classified as a primary
standard: A drift-free unit has yet to be constructed.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
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Never attribute to malice what can adequately be explained by incompetence.
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