On 04/27/2014 04:15 AM, Tom Van Baak wrote:
The thunderbolt is one of the best timing devices but not for frequency, if
you want high resolution. Over time it is ok but high resolution short
gate times and you see the frequency changes. They use the OCXO to correct for
timing error and if you have a Tracor 527E you can see it. Also how else
do you think they control the 1 pps.
Bert Kehren
Hi Bert,
Put your TBolt (or any other GPSDO) in holdover (freeze the DAC) and then take
a close look again. Tell me what you see. The difference (if any) is due to
steering. What's common (if any) is due to the OCXO itself.
Have a look at http://leapsecond.com/pages/gpsdo/ to see the results for 4
common GPSDO. Focus on the left edge of the plots only. Note also that tuning
parameters can make a big difference in the results (I used only defaults for
those plots).
The Pendulum GPS-88 and GPS-89 have a button on the front you push when
you want to force it into hold-over to do your measurement, for this
very reason.
PPS steering and OCXO steering is the same thing once you forced the PPS
into the right range. Some *really* depend on the synchronicity between
10 MHz and PPS, and you should not obscure it if possible.
Cheers,
Magnus
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