[time-nuts] FE-.5680A trimming resolution

Tom Van Baak tvb at LeapSecond.com
Wed Feb 1 00:21:40 UTC 2012

> Let's say, i'm building a GPSDO with a high quality OCXO.
> Wouldnt it then make sense to lock the reference clock of the GPS
> receiver also to that OCXO?
> Attila Kinali

It's a design decision. Most GPSDO sold are made by companies
that buy an OEM GPS timing receiver and then create a GPSDO
with the usual assortment of OCXO, TIC, computer and DAC.

The exception would be if you are a GPS company and can
integrate the components, as Trimble did with the Thunderbolt.

But most companies selling GPSDO, and all amateurs building
homebrew GPSDO, have to use the separate component method.

Note the really high-end GPS timing receivers use an external
reference clock and don't even bother to lock it. The advantage
with this is 1) you don't need the DAC (which just adds noise),
2) you can use good clocks like cesium or masers which don't
have EFC, and 3) you collect the phase error information for
post-processing -- which is much more accurate than trying to
steer an oscillator in real time. And also, 4) you can run multiple
receivers off the same clock if necessary.

We're waiting for some brave soul to implement an SDR-based
GPS timing receiver; we can all then experiment with the TBolt
model instead of the TIC/DAC model of GPSDO.


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