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

Tom Van Baak tvb at LeapSecond.com
Wed Nov 7 16:05:21 EST 2007


> George for a single ground pin OXCO you might want to consider
> compensating  for the oven's internal ground bounce. The voltage drop
> caused by a normal  heater current is around 1/4 to 1/2mV for an MTI
> 260 oven.

> All I can add in regards to the Fury GPSDO is: the EFC control  voltage
> ground, and heater ground MUST be Kelvin-sensed.
>
> Any ground loop error above about 10 - 50 microvolts would affect the
> systems' accuracy on good double oven OCXO's.

Hal, Said, and others,

I need convincing that this single-ground-pin OCXO worry is
valid.

During the first few minutes of oven warm-up one can expect
large variations in heater current. But during this time no one
is concerned with EFC stability. So we ignore that case.

After that, oven current is relatively constant by comparison.
In a GPSDO the EFC is part of a closed loop. So even if there
is a small voltage offset in the EFC control or return path due to
heater current, it seems to me that it still has no effect on either
the accuracy or the stability of the GPSDO. So we ignore that
case too.

Is the worry, then, about the minor ambient temperature related
variations in steady-state oven current? Or something else?

/tvb




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