[time-nuts] Comparing PPS from 2 GPS units

lists at lazygranch.com lists at lazygranch.com
Thu Dec 13 10:25:12 UTC 2012

They make frequency difference meters. I never used one, but it seems to me a frequency difference meter would just use the two input signals to toggle up and down respectively on a counter, then display the result over a fixed period.

Would this do what you want?

------Original Message------
From: Hal Murray
Sender: time-nuts-bounces at febo.com
To: time-nuts at febo.com
ReplyTo: Discussion of precise time and frequency measurement
Subject: [time-nuts] Comparing PPS from 2 GPS units
Sent: Dec 13, 2012 1:57 AM

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?

These are my opinions.  I hate spam.

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