[time-nuts] Comparing PPS from 2 GPS units

David davidwhess at gmail.com
Thu Dec 13 23:59:55 UTC 2012

On Fri, 14 Dec 2012 00:06:15 +0100, timenuts at triplespark.net wrote:

>On Dec 13, 2012, at 4:57 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
>> Suppose I want to compare the PPS outputs of 2 GPS units.  The problem is
>> that I don't know which one will happen first.
>> If I feed them into the start/stop inputs of a typical timer/freq box, I
>> don't know which is which.  If I get them wrong, the answer will be
>> 0.999999xx seconds rather than the -0.000000xx that I want.
>> [...]
>> Do any of the counter/timer boxes have a mode for this?  If so, is there
>> a buzzword I've overlooked?
>Counters like the Agilent 53230 actually WILL output negative delays 
>in this case as long as the delta is still small. This is a quite useful 
>feature in such cases...

I was thinking along those lines but as far as I can tell from the
manual, the Racal Dana 1991 and 1992 only measure backwards to -2
nanoseconds which I have just verified with a 50 nanosecond rise time
pulse and fiddling with the A channel and B channel trigger levels in
common mode.  I remember seeing the same thing when using a 2
nanosecond calibrated delay coaxial patch cable.

More information about the time-nuts mailing list