[time-nuts] Trimble Thunderbolt setup optimization and adding a10811 OCXO

Tom Van Baak tvb at LeapSecond.com
Mon Jul 13 20:25:27 UTC 2009


> yes that is what I thought, but if I do observe correct, TB's 
> OCXO does not run at all free for minutes. With a time 
> constant of 360s the EFC and thePPS is surfing up and 
> down, why, I do not see the need to shift this OCXO within 
> 2 minutes 80ppbs up and pps15ns as well - with this stable 
> oscillator....what is the driver, the SATs (I think not so)!
> 
> Arnold

First, are these 80ppbs and pps15ns numbers externally
measured by you or internally reported by tboltmon?

It's not that the OCXO runs free for N seconds and then is
corrected and then runs free for another N seconds and is
again corrected, etc. Most GPSDO seem to "continuously"
adjust the DAC. Exactly how much how often depends on
a lot of factors. For example, if you look closely the Z3801A
DAC effectively changes about a hundred times a second:
http://www.leapsecond.com/pages/z3801a-efc/

Play with the TBolt time constant to see what happens. If
you have a particularly stable TBolt and a very stable lab
environment then you should be able to increase the TC
which may improve the shifts that you see. For example:
http://www.leapsecond.com/pages/tbolt-tc/

/tvb





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