On 2012-01-10, David J Taylor <[email protected]> wrote: > "David Woolley" <[email protected]> wrote in message > news:[email protected]... > [] >> To the extent those constraints don't apply and both ends are terminated >> well above the characteristic impedance, the output voltage actually >> goes up in a staircase, with the steps being the round trip time. >> >> Some other mistermination conditions cause a ringing approach to the >> final value, which is why it is better to operate with a high impedance >> load, and therefore capacitive characteristics. > > I wish Chris would just look at the remote signal with a 'scope! A wide
Needs a reasonably good scope. > pulse over the length of line he talks about should be no problem at all > (but a microsecond-wide pulse might). The timing PPS I've seen are in the > tens of milliseconds wide. If there is overshoot, perhaps a capacitor to Did you mean 10s of ns? The Sure width is about 5-10ns. at the card without any line attached. The line could certainly broaden that up to about 1us, but ms? Even the Garmin 18 is less than a usec. > slow things down might help, or on the other hand, if the edge is too slow > providing a better match might help. > > Of course, "clean" transmission does rely as I said before on each signal > being provided with its own ground in the twisted pair, a point also made > by Bill Unruh. For PPS a screened 50-ohm coax cable is not needed except > in extra ordinary circumstances (exceptional noise or sub-microsecond > accuracy). Even level converters may not be needed - even though the > specification says so. Many RS-232 ports work just fine with TTL levels. > > Cheers, > David > _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
