[time-nuts] Precise Time transfer and relative position over ashort baseline

[Tom Van Baak]

Bruce,

So the time tag information will be processed off-line. In that case there's no requirement for real-time clock synchronization, is there? Why not let each station's clock free-run and provide periodic external pings amongst the stations as a way to continuously calibrate all the pair-wise clock drifts.

Since you don't want coax or fiber perhaps multi-round-trip RF or laser pulses could be used, NTP-style. From this you get the phase drift of each clock relative to its neighbor(s). The clocks need to be stable below 100 ps but do not need to be accurate or disciplined. You simply apply the measured paper clock corrections to the observed time tags.

Another way might be to use single-channel common view GPS. I've not checked recently to see if 100 ps is possible over a 1 km baseline. If so that would be a less expensive solution. Someone should dig into the RINEX mode of the ublox 6T. It's on my list but the list is long.

/tvb


----- Original Message ----- 
From: "Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
To: "Discussion of Precise Time and Frequency Measurement" <time-nuts at febo.com>
Sent: Sunday, April 10, 2016 10:00 PM
Subject: [time-nuts] Precise Time transfer and relative position over ashort baseline


There is a proposal to use multiple light bucket style optical telescopes to do Intensity stellar Interferometry over short baselines (up to perhaps 1km or so) by using independent clocks to time tag photon arrivals. store the time tags and process the data off line. Depending on the time tag resolution there is a need to measure the time differences between the independent clocks to an accuracy in the 1ns to 100ps range. Is there a better way of doing this other than using geodetic grade GPS receivers capable of GPS carrier phase measurements?Since the local clock flywheel oscillators will need to not deviate by more than 100ps or so over the several minutes required to perform the carrier phase averaging what sort of clock will be suitable apart from a good rubidium standard with a cleanup oscillator?
NB Running fibres or coax between the telescopes isnt an option.

The relative positions of the telescopes has to be known to within a cm or so for this to work.
Bruce

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