[time-nuts] Re: Why do have OCXO a Vref output? (was: help reviving Trimble UCCM-LPS GPSDO)

[Andy Talbot]

In the (very) few OCXO circuits I've seen, voltage at both ends of the
tuning varactor are derived from the same internal voltage reference.  So
any drift in this will, partially at least, cancel out.    I too was
surprised to see nothing more than a Zener being used in one case, but
bearing in mind this was in a temperature controlled environment is not as
bad as a Zener in open air

Andy
www.g4jnt.com



On Sat, 25 Dec 2021 at 16:26, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:

> Being also a bit of a volt-nut, I played a bit with the Vref output
> from some of my OCXO's and must sadly report that they were not
> spectacular, seen from a volt-nut perspective.
>
> In at least once case, an admittedly pretty old OCXO design, the
> voltage reference was not located in the most well-regulated part
> of the oven and the chosen chip had pretty bad tempco at the elevated
> temperature.
>
> --
> 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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