David J Taylor wrote: > 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!
Are you getting better than 10us offsets though? :-) I've no idea how much signal degradation there would be using utp for pps and will both put it on spice and keep the spare pair in cable free to give it a try. However I'm making up various pcbs so an extra couple of tiny jobs won't add much to the fun and is playing safe in case I end up mounting aerials on roof or in garden, although that looks very much less likely to be needed now. > 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. That's another project, putting the servers in a cupboard with temperature control. Alternative of locating the crystals and fitting heater is also a possibility. Cupboard idea has advantage of cutting down noise and will help keep the pcs from overheating. David _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
