[ntp:questions] NMEA ref.clock better than my ISP's timeserver?

David J Taylor david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid
Fri Jun 12 09:08:37 UTC 2009

Unruh wrote:
> I use cat 5e cable since it is cheap, available and is supposed to be
> good for better than about 100MMHz
> (10nsec) signals. I would not use usb cable or any old wire, because
> of
> the problems of spread of the pulse from the gps. Also I would
> terminate
> it properly as well so that signal  reflections could be problematic.
> on
> long runs.
> If the run is less than 10m it should be ok even with improper
> termination.

Cat 5e cable sounds like a good compromise.  On very long runs, you would 
not only need to terminate the cable correctly, you would need to drive it 
correctly as well, requiring powered line drivers and receivers at either 

In the OP's case, the run is only 30m (i.e. about 100-150ns) so the effect 
of reflections on a system (RS-232) which is bandwidth-limited to a 
microsecond or two should be very little, and I would likely use the cable 
in an unbalanced configuration.


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