[time-nuts] Rb vs.Crystal OCXO

Magnus Danielson magnus at rubidium.dyndns.org
Sun Apr 27 04:20:46 EDT 2014



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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