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04/30/2006 Entry: "Clock Setting"

I've just set the PPS offsets for CS1, CS2 and RB1 to make it easier to do clock comparisons. The idea is for them to fire in this order: RB1, CS2, CS1, GPS.

To accomplish this, I used GPSDO2 as the starting point. It's set in software to run 10us early versus GPS. Its 1pps went into the HP 5359A time synthesizer, which adds an additional adjustable delay.

The result is that as of right now, CS1 is nominally 5us early vs. GPS; CS2 is nominally 7.5us early; and RB1 is nominally 10us early (RB1 is set directly from GPSD02). And, for what it's worth, GPSDO1 is nominally set as close to GPS time as I can get it, taking into account cable delays.

So much for the nominal delays; the synchronization process introduces some uncertainties of its own. In particular, CS1 has the original HP clock with adjustable divider, while CS2 and RB1 have aftermarket clocks. The measured delays versus GPS (100 second averages via M12+T and HP 5370B) as of right now are:

CS1 -- 5.030us
CS2 -- 6.635us
RB1 -- 10.228us