Tom Van Baak said the following on 05/30/2009 03:44 PM:
... as long as you remember to use TI+/- mode.
For stuff like this I use plain old TI mode and just set the
UUT 1pps to lag the reference 1pps by a fraction of a
second, or maybe even just a couple of microseconds.
That way you get a small positive time interval reading
every second.
For what it's worth, I evolved a system where one of my GPS units and
one of my Z3801A run as close to UTC(GPS) as I can get, taking into
account cable delays, etc.
I run another Z3801A at about 500uS early relative to GPS. Then, I use
that 3801A and an HP 5359A time synthesizer (which can generate delays
of up to 180ms) as the reference when I sync the dividers in the clocks
that I am monitoring.
I set up a hierarchy -- with the nominally highest drift rate clock set
maybe 250uS early, the next unit 150uS early, and the final unit 50uS
early. Now, I can compare #1 against #2, #2 against #3, and any of them
against GPS using positive TI. (This assumes the convention that the
DUT goes on the START input, and the reference on the STOP input.) I
can usually take data this way for quite a while before any of the units
cross over.
John
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