Frequency Reference for NTP Use?
Alex Satrapa
grail at goldweb.com.au
Fri Jul 12 17:47:08 EST 2002
I'm trying to hook up my Garmin GPS-II+ GPS to use as a reference clock
for xntpd. Unfortunately, there's just way too much jitter (the NMEA
driver has to parse the time out of a lot of cruft including such
useless information as the current physical location). I'm hoping that
it might be possible to get a reference of some sort that can provide a
1PPS signal to discipline the GPS clock (ie: use the GPS to provide the
time stamp, use the PPS to provide the exact time).
Has anyone else been looking for frequency references/standards? All
the things I've found insist on being GPS clocks too, and they generally
cost in excess of $US1000. I just don't have that much money lying
around to spend on a clock.
Ideally, I'm looking for a 1PPS source with an RS-232 or Parallel port
interface, that has accuracy as low as a few seconds a month (which
means I'd be happy with a Quartz oscillator). I would love to have a
Caesium clock, but I just can't scrape up the $1M odd that I'd need ;)
My biggest reasons for avoiding GPS-based external clocks is that:
1) I already have a GPS
2) I don't want to rely on the GPS network for my time (I may not be
able to receive the signal)
I'm wondering whether I might get away with building my own oscillator
from a 10MHz crystal and just triggering the "CTS" line (or whatever)
every 10M cycles - but I'm thinking it would be cheaper to buy someone
else's proven technology.
Alex
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