[time-nuts] Comparing PPS from 2 GPS units
lists at rtty.us
Thu Dec 13 11:52:11 UTC 2012
The easy way to take care of the problem is to program one of them with a cable delay of around 500 ns. The GPS should not be outside +/-100 ns, so that's plenty of room for a start / stop to occur. Of course that assumes that the GPS has a programable cable delay setting.
A 500 foot spool of cheap coax from the local big box store would be the other answer. You may need to fiddle a little with the terminations on it. Some of the cheap coax really isn't quite the impedance you would think from the "75 ohm coax" label on it ….
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.
> 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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