[time-nuts] Comparing PPS from 2 GPS units

David davidwhess at gmail.com
Thu Dec 13 17:00:41 UTC 2012

If the trailing edge of one of the pulses is reliable, you could
measure from the starting edge of one pulse to the trailing edge of
the other pulse.

It is not impossible to make an adjustable but accurate pulse delay
using a comparator or maybe a gate.  How accurate does your
measurement need to be?

Setting the cable delay like Bob suggests would be the easiest.

On Thu, 13 Dec 2012 01:57:34 -0800, 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.
>Is there a simple solution for this?
>My straw man is to use the antenna cable delay setting to offset one of the 
>PPS pulses a long way.
>Plan B would be a physical delay unit.  But they are probably temperature 
>sensitive, and I'm not setup to keep anything at a constant temperature.
>Do any of the counter/timer boxes have a mode for this?  If so, is there a 
>buzzword I've overlooked?

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