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

Nick Sayer nsayer at kfu.com
Wed Aug 17 14:51:07 EDT 2016

Updating the EFC more quickly reduces the ADEV, though. I find that the fiddly part of tuning a GPSDO design is balancing the ADEV against phase control. If you want keep an iron fist on the phase, you can only do so by constantly swatting around the frequency.

I won't say that getting more frequent phase feedback is a bad thing, but if you're trying to get the PLL time constant to be longer rather than shorter that it won't help a lot. 

Sent from my iPhone

> On Aug 17, 2016, at 9:57 AM, Peter Reilley <preilley_454 at comcast.net> wrote:
> You can get crystal oscillators that have a frequency control signal and are more
> stable than the run of the mill oscillators.   Changing the GPS oscillator would
> require modifying a very tightly populated circuit board.   Perhaps not possible.
> What about some of the SDR (software defined radio) projects that aim to
> implement GPS functionality?   If you used the GPS chipping rate (1.023 MHz)
> to dicipline the 10 MHz oscillator then you are less sensitive to crystal instabilities.
> You are updating the crystal one million times a second rather than once per second.
> This is assuming that the chipping rate of the transmitter is just as good as the
> 1 PPS signal.   This info from here;
> https://www.e-education.psu.edu/geog862/node/1753
> and here;
> https://en.wikipedia.org/wiki/GPS_signals
> Even using the 50 bits/sec data rate of the GPS signal would allow updating the
> GPSDO faster than the 1 PPS signal.
> Pete.
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