[time-nuts] GPS 1 PPS Averaging ?

Bill Hawkins bill at iaxs.net
Sun Mar 13 17:39:55 EST 2005


What if I use two clocks and a Time Interval counter?

I'd apply the sawtooth 10 MHz output to a decade divider and
feed 1 MHz to a Datum 9300 time code generator. The generator
provides a day-time clock and a 1 PPS output

I'd apply the standard-under-test 10 MHz output to an identical
divider and time code generator, also getting time and 1 PPS.

I'd expect some systematic errors from the rise and fall times
of all of those SSI and MSI chips, but I can make the measurement
interval long enough that those errors fall off the end of the
time of year plus TI counter digits.

I don't need high-speed computer input (which, I think, takes
the fun out of it for most of you). I sample the counter once
an hour while I tweak the standard down to 10E-10 error, using
100 ns resolution on the counter. The standard won't move any
faster than that, so there's no point to more resolution.

If I could sample every counter reading, I'd know exactly what
the maximum reading error would be. Then I'd adjust the sampling
times to swamp the reading error.

This procedure does not yield fast results, but it is very
accurate when the sources of errors are not known quantitatively.

Of course, you can't do this without a UPS - or converting
everything to run from batteries. That leads to an assortment
of batteries and chargers.

Bill Hawkins

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