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

[EWKehren at aol.com]

I have three 5071  10811's all have below 1 E-12  AV from 1 to  100 seconds.
Bert Kehren
 
 
In a message dated 11/5/2012 7:07:52 P.M. Eastern Standard Time,  
richard at karlquist.com writes:

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


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