[time-nuts] GPS discipline oscillator vs phase lock

Lifespeed life_speed at yahoo.com
Sat Jun 17 17:07:32 EDT 2017

Yes, one has to lock them at a high reference frequency so as to avoid multiplied-up phase noise.  I can manage the tracking loop design.  Some applications aren't line-of-sight, so the radio link doesn't solve every situation.  Fiber optic backup plan, but everybody hates cords.

This is my application as well, phase measurement of the signals separated by some distance.  Not a billion km, but even a few km requires similar considerations.


-----Original Message-----
From: jimlux [mailto:jimlux at earthlink.net] 

Well, at JPL we regularly lock two crystal oscillators together that are over a billion km apart with added Allan deviation of less than 1E-15 at
1000 seconds with a radio link at 7.15 GHz.  It's how we measure the distance and velocity to spacecraft (a few cm in range and mm/s in
velocity) and from that figure out the gravitational fields (among other

So it is *doable*

The performance depends ultimately on the noise within your tracking loop bandwidth.

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