David J Taylor wrote:
"David Lord" <[email protected]> wrote in message
news:[email protected]...
[]
I've not put a scope on the pps but I added an extra section
of cable from my Sure GPS, 18 m of 4 x pair telephone cable.
I will need that length to reach from the GPS down to my PCs.
In the process the offset jumped from 0.004ms to about 12ms
but fairly quickly went back to a few usec.
PC = me6000 (VIA ME6000), NetBSD-5, ntpd 4.2.6p5
From my ntp-stat file:
time offset(ms)
15:06 -0.004
15:12 0.000
15:18 0.001
18:24 0.006 extra 18 m cable added
15:30 -12.938
15:36 -3.672
15:42 -0.814
15:48 -0.186
15:54 -0.054
16:00 -0.012
16:06 -0.006
16:12 -0.002
16:18 -0.002
16:24 -0.001
David
David,
I suspect that the offset jump was purely from losing the PPS signal,
and nothing to do with the extra cable as such. BTW: I think your
editing accidentally included the time - from 15:24 to 18:24. Must have
had "18" on the brain! <G>
I didn't spot that until after I'd posted.
My comments on wiring are as before - use one line from each pair as
ground, and then the other four "active" lines become TXD RXD PPS and
+5V power.
Nearly that, but I'm splitting the power and planning on
having +9V and -Ve on two of the lines and a 5V regulator
since some of the GPS modules with interfaces take over
200mA so common OV with the -Ve at the far end should
remove any effect from voltage drop over that length of
cable.
I might try rs422 for the PPS (and TxD lines) but they
are 16-pin chips and have unused sections. The 8-pin
versions with single Tx + Rx are much too expensive.
David
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