On 6/16/17 10:55 PM, Lifespeed via time-nuts wrote:
Not too surprising to read locking two crystal oscillators together
without using a physical cable is difficult to impossible.
Essentially what I am looking for is the phase alignment accuracy
(and phase noise) one would get PLL’ing one oscillator to the other
using a cable, but over a longer distance. Some modest phase noise
degradation might be acceptable, but not an order of magnitude.
Clearly not a trivial problem. Yes, the jitter (phase noise)
typically accomplished from a PLL phase comparing at 100MHz is better
than what one could get “locking” to GPS. It was just a thought,
apparently not a realistic one. Thanks for disabusing me of that
notion.
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
things)
So it is *doable*
The performance depends ultimately on the noise within your tracking
loop bandwidth.
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