[time-nuts] Fury Interface Board: 5MHz needed?

Tom Van Baak tvb at LeapSecond.com
Wed Nov 7 17:37:41 EST 2007

> Tom
> Even without frequency disciplining it doesn't appear to be a
> significant issue (if we accept Peter Schmelcher's data) for OCXOs like
> the MTI 260 and 230 series as this effect is swamped by the frequency
> tempco due to other effects such as the finite change in oven
> temperature due to the limited thermal gain etc.


Thanks. Here's my math. An average 10 MHz OCXO has an
EFC range of, say, 1e-7 over 10 V. That's 1e-8/V; 1e-11/mV.

Now look at the short-term frequency error of a Fury:
( from http://www.leapsecond.com/pages/fury/ )

You see Fury frequency varies by at least 5e-11 over minutes,
as is normal for this class of OCXO. To make that much noise
with EFC effects alone you'd need on the order of 5000 uV
variation on EFC line. Another reason why I think the single
ground pin question is a non-issue.

The steady-state oven current variations are quite small. See
this plot, for example:

Said, have you measured the ground return loop resistance on
a Fury? We can do the rest of the calculations based on that.


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