On 2/19/15 9:11 AM, Matt wrote:
Hi,
My university would like to have a <1ms precise source of time to do
some networking experiments (measure one way propagation delays
etc...). So I wandered on the internet to find the best choice with a
budget of ~1000€ (~1100 American dollars).
I've been overwhelmed by the number of possibilities (atomic
clocks/GPS signal etc...) and as no price appear on the seller
websites, it's difficult to rule out options.
An inexpensive GPS receiver with a 1pps output will easily get you to
much better than 1 millisecond. The Garmin 18 is but one choice. It
has the advantage that it's already packaged, as opposed to, say, one of
the little modules designed to be attached to a Arduino.
Configuring ntp to use it is just a matter of setting up the file
properly. NTP will use the 1pps coming in on one of the modem control
signals (DTR, DCD, RI, etc.)
(I use a USB cable to get 5V to run my GPS-18x-LVC, and wire 1pps to
DCD, pin 1 on the 9 pin connector)
So really, it's a matter of finding a place to put your Garmin receiver
and string a cable that's not too long to your *nix box running ntp.
People have done it with a Rpi, if you want to go that route.
I also read good comments on Garmin 18 hardware but it is so cheap I
wonder if it precise enough.
I wonder if we should buy a specific box or if we could not plug the
antenna to a linux box with gpsd/NTPd on it ?
That's exactly what you want to do.
http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm
http://www.rjsystems.nl/en/2100-ntpd-garmin-gps-18-lvc-gpsd.php
(everything there should work fine with the current GPS-18x-LVC, but I'm
sure someone on the list has actually done it and can confirm.)
http://www.catb.org/gpsd/gpsd-time-service-howto.html
Yeah, the Garmin is cheap ($85 US), so you're not going to get
nanosecond timing, just microsecond level. Since you need milliseconds,
it's plenty good enough.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
