[time-nuts] SE880 GPSDO

[Mike Cook]

> 
> Assuming that you have an amateur radio license, you could use a 
> well located central station to transmit a CW signal in the 70cm or
> 23cm band. There should be some effort put into this station
> to make it stable (eg by using a good rubidium as frequency source,
> or even an ensemble) and low noise.
> 
> Use this CW signal on all the telescope stations to phase lock a local
> OCXO. Using a good OCXO, it should be possible to use loop bandwidths
> in the 0.1-10Hz range. My guess is, that this frequency transfer system
> would yield stabilities in the order of 10^-12 @ 1s (or even better).
> For additional performance, one could modulate the CW with a PRN sequence
> to get a better SNR and probably get another order of magnitude out of it.
> For the simple CW case, the circuitry should be fairly simple and easy
> to do. The PRN case would require at least some processing in an FPGA.

It might be possible to clock the FPGA directly from a suitably massaged CW. Do any clock at 1GHz+???
It would be also possible to do away with LO’s in this case. 

> 
> Now that all stations have the "same" frequency, one can use the GPS
> module to get the time information using long integration times.
> Under the assumption that the (sawtooth corrected) PPS is good to +/-10ns
> an has a nice, time-invariant distribution, it should be possible to get
> below 1ns in precision within 100s. Using common view phase data it
> should be possible to get even better than that. 

The CW could also carry time, and if it was feasible, local GPS would be unnecessary.
The  telescope sites would receive the ticks at different times but the delta could be post processed out provided the positions are known to a few centimeters.

> 
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