[time-nuts] Fine frequency adjustment in 5370B

Tom Van Baak tvb at leapsecond.com
Sun May 15 19:07:38 EDT 2005

> Hi Tom,
> I was aware of the accuracy of the timebase for TI measurements is not 
> that critical, and TI measurements were my reason for buying the 5370B 
> rather than a normal frequency counter.
> However, the fact remains the 5370B is a better *frequency* counter than 
> any others I have, so having the oscillator as close as reasonably 
> practical, without necessarily having to have it locked to a GPS unit, 
> would be useful to me.

Makes sense. You're all set then.

One more thing for everyone to consider -- many
counters, such as the 5370, have an input for an
external timebase and this solves the problem of
having to keep the internal OCXO calibrated all
the time.

However, one word of caution. If you are using the
5370 (or equivalent) to make short-term stability
measurements then be aware of possible accuracy
vs. stability trade-off.

For greater accuracy most people use a rubidium
or cesium or GPSDO as the external reference.
But these more accurate sources, in some cases,
may have less short-term stability than the internal
10811 OCXO.

A PRS10, for example, may have 100x or better
accuracy than a typical 10811. Yet a 10811 can
easily have 2x to 10x better short-term stability
than a PRS10. You can indirectly measure this
by seeing which reference, internal or external,
gives the smallest standard deviation for the
particular measurement you are making.


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