[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 10:50:17 UTC 2009

David Lord wrote:
> First I don't think there's any problem getting the nmea down
> twisted pair at 4800 baud.

.. agreed, but .....

> To play safe with the ttl level pps I've setup to use a simple
> emitter follower that can drive into 75r coax.
> I didn't want to use line drivers as I don't have any handy that
> work off single 5V supply.
> I need a converter back to ttl before going to pc and don't have
> any spare gates in the box with compulsory flashing led and
> ticker, so will use another couple of transistors wired as
> Schmitt trigger.
> David

I think you're needlessly overcomplicating the PPS signal.  I have the GPS 
18LVC feeding /two/ parallel RS-232 interfaces, /and/ a low-current LED, 
so for a 30m length I think you would get away with a simple wire 
connection.  However, have fun with the soldering iron!

If you're seeing 4us offset now, that may be as good as it gets.  You may 
need a more constant temperature to see better.


More information about the questions mailing list