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

[Peter Reilley]

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.