[time-nuts] FE5680 GPS Disciplined Controller Update
SAIDJACK at aol.com
SAIDJACK at aol.com
Tue Jun 24 17:07:30 EDT 2014
airflow, or changes in airflow are typically much worse for ADEV than
actual ambient temperature changes in still air.
In still air for example a typical Eurocan DOCXO will have a case temp of
about 55C to 60C at 25C ambient.
Turn on any kind of significant airflow over that part and the air
temperature will be nearly the same as before, but the case of the DOCXO is now
very quickly cooled to 30C to 40C by the airflow.
This affects mostly TCXO and single-oven units (including Rb's etc), it
does very little to DOCXO units typically because the outer oven takes the
brunt of the temp change and insulates the inner oven. There are other
components on the PCB though next to the DOCXO that will be affected such as the
DAC, DAC reference, EFC filters, current ground loops due to changing
heater-current on the ground pin, etc.
This even affects TCXO's because they are typically heated by themselves
and other components on the PCB, and any kind of airflow change will cause an
instant temp change on the TCXO due to cooling.
So in my opinion a bang-bang controlled fan near any kind of oscillator is
about the worst thing one can do for short term stability.
In a message dated 6/24/2014 13:35:21 Pacific Daylight Time,
tvb at LeapSecond.com writes:
> However it is disappointing that no one has stepped up to tackle the
> temperature problem. how many have looked at the temperature attachment
> clicked on the N5TNL link. Let me make it clear that yes the GPSDO will
> there will be one or two orders of magnitude degradation without active
> fan temperature control unless the internal temperature compensation is
Can you clarify the "two orders of magnitude" claim? That's hard for me to
believe, I think, without seeing the ADEV plots or actual lab report.
I mean, even a cheap XO or TCXO or OCXO can be disciplined against GPS and
achieve superb results. Temperature (or rather, temperature rate of
change) has little effect short-term. Temperature also has little to zero effect
long-term. So it's only in the, what, tau 100 to 1000 or maybe 10000 second
range that temperature even matters. As long as the LO is locked to GPS; I
assume you're not talking about holdover.
Obviously you'd want a slightly shorter loop time constant for a
non-temperature-controlled Rb than a fancy temperature-controlled Rb. But does this
really make a one or two *orders of magnitude* difference?
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to
and follow the instructions there.
More information about the time-nuts