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_...@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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