[time-nuts] OCXO Vref (in)stability plot

[Poul-Henning Kamp]

Ok, this surprised me a LOT!

I used my HP3458A to measure the stability of the Vref output from
an IsoTemp OCXO-107 and the results were anything but stellar:

The OCXO's Vref has 18 microVolt RMS noise

For comparison my HP6626A power-supply has 2 microVolt RMS noise.

Obviously, the Vref only has to be good enough to not be a relevant
source of noise when used on the EFC input.

If the OCXO has a EFC sensitivity of 10PPM/Volt, then a microVolt
more or less means a 1e-11 change in frequency.

The Vref is also quite sensitive to the OCXO supply voltage, but
since it was powered by the HP6626A, that's not where the noise
comes from.

Plot attached...


-- 
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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