[EMAIL PROTECTED] (Folkert van Heusden) writes: >> > day, but I think that was for long distances, bouncing off the >> > ionosphere which changed height at night. I'd expect it to be >> > pretty stable if you are close to the transmitter - ground wave. >> >> HBG is in Switzerland if I remember correctly, and from your post, you are >> in Netherlands,
>correct >> so you can estimate propagation delay. However, I don't see >> why you would want to use an LF reference of lesser accuracy and estimated >> delay when you can use GPS. >> Just a thought. >Well if I remember correctly someone said to me once that the >time-string returned by cheap gps device (like my garmin 18 lvc) >sometimes is a bit off while its PPS signal is fine. Yes, the pps is stated to be accurate to better than a microsecond. The interrupt time on your system when quiet is a few microseconds. The NMEA response string is maybe good to a few msec at best ( even subtracting out the "average" delan due to the length of time it takes to read the string). Ie, the fluctuation in the string read time is probably like 10ms, a factor of about 10000 worst than the pps. Yes, 185 ms is about how long it takes to read the nmea string (about 70 characters as 4800 baud is about 1/6 of a second) YOu can tell ntp to subtract off say 180ms but that would still leave you with a sizeable jitter. >Currently I'm syncing against NMEA/PPS and seeing quiet a big offset: For what? This looks exactly like what I would expect. > remote refid st t when poll reach delay offset jitter >============================================================================== >xGPS_NMEA(0) .GPS. 0 l 7 16 377 0.000 -185.08 1.001 > <--- > PPS(0) .PPS. 0 l - 16 0 0.000 0.000 0.001 > <--- >-muur.intranet.v .DCFa. 1 u 5 64 77 0.072 -9.207 0.023 >-thegateap.intra .SHM. 1 u 46 64 37 0.873 0.931 0.045 > SHM(0) .SHM0. 2 l - 64 0 0.000 0.000 0.001 > SHM(1) .SHM1. 2 l - 64 0 0.000 0.000 0.001 > SHM(2) .SHM2. 2 l - 64 0 0.000 0.000 0.001 > SHM(3) .SHM3. 2 l - 64 0 0.000 0.000 0.001 > NTP.MCAST.NET .MCST. 16 u - 64 0 0.000 0.000 0.001 > 192.168.64.0 .BCST. 16 u - 64 0 0.000 0.000 0.001 >-auth1.xs4all.nl 194.109.22.19 3 u 48 64 77 7.945 1.514 1.158 >-auth2.xs4all.nl 193.67.79.202 2 u 46 64 77 9.450 -0.893 0.713 >+ntp1.nl.uu.net .GPS. 1 u 45 64 77 13.693 0.173 9.097 >*chime2.surfnet. .GPS. 1 u 111 64 76 12.262 0.387 1.092 >-superboer12.stu 193.79.237.14 2 u 45 64 77 13.012 4.401 2.248 >+ntp.networking4 193.190.230.65 2 u 46 64 77 9.242 0.444 0.494 >+mailer.zylom.co 193.190.230.65 2 u 44 64 77 9.040 0.430 0.538 >-aivd.xelerance. 193.0.0.228 2 u 41 64 77 8.881 -0.610 3.154 What are you doing? Why all of these sources? _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions