[time-nuts] GPSDO - probably a stupid question.

["Björn Gabrielsson"]

Some (all?) Novatel receivers have an option to sync their internal TCXO
or let it freewheel.

--

     Björn

> The stability of the typical GPS receiver oscillator is usually inadequate
> to be useful as a GPSDO. An OCXO (as in the Trimble Thunderbolt for
> example) or equivalent is usually required. One can't usually just add a
> varicap to adjust the frequency of a packaged oscillator. If an external
> crystal is used the varicap should be placed in series with the crystal.
> However to do this reliably one needs to know the crystal parameters and
> those of the oscillator circuit. If you need to adjust the frequency both
> up and down (due to crystal parmeter tolerances) then an inductor in
> series with the crystal and varicap will also be required.
> Bruce
>
>
>     On Wednesday, 17 August 2016 7:05 PM, Peter Reilley
> <preilley_454 at comcast.net> wrote:
>
>
>  As a neophyte, I was wondering: rather that trying to discipline an
> external
> oscillator to create a GPSDO and produce a precise 10 MHz why not
> discipline the oscillator
> of the GPS receiver itself?  This could be done with a varactor diode
> across crystal of the
> receiver's oscillator.  Of course there are the same problems with
> trying to servo this
> oscillator as there are trying to servo an external oscillator but there
> are fewer parts.
>
> Being a beginner I assume that I am missing something, but what?
>
> Thanks,
> Pete.
>
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