[time-nuts] getting a grip on 10811 drift (beginner-ishquestion)

[Rick Karlquist]

Bob Camp wrote:
> Hi
>
> If you have one of the 10811's out of a Z3801, then it's EFC range is ~
> 10X
> a "normal" part. There apparently are other odd EFC ranges out there.
>
> Bob
>

For example, the 5071A cesium standard has 10X range (modified 10811).
I guess in the 5061 you just had to tweak the mechanical trimmer
occasionally if the xtal osc drifted out of range.  With all the
other maintenance on the '61, this didn't seem like much of an
additional burden.

We wanted to make the 5071A "automatic" and convinced ourselves we
could get away with increasing the EFC range.  There were two issues
with this:  one was the possible lower Q of a hyperabrupt varactor.
We determined that there was nothing risky about hyperabrupt diodes.
The other issue was contamination due to either the 10811's internal
Zener reference or the external DAC.  The Zener reference diode,
according to the designers, is a "low noise" Zener (I don't know
if it is the "buried" type), but anyway, it is a legacy part,
but a known good legacy part.  The 5071A DAC was a very carefully
designed one that was good enough.

Rick Karlquist N6RK