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devel / comp.protocols.time.ntp / GPS+PPS vs NTP server, why such a large offset ?

GPS+PPS vs NTP server, why such a large offset ?

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Subject: GPS+PPS vs NTP server, why such a large offset ?
From: planetibo@gmail.com (Thibaut HUMBERT)
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by: Thibaut HUMBERT - Thu, 16 Jun 2022 07:22 UTC

Hello,
I post this message because I have a huge offset (+110ms) on a PPS source compared to NTP internet servers.

My hardware :
I use a USB<>TTL adapter (CH341A) connected to a NEO-6M in +5V, RX, TX, GND. I soldered pin 3 of the u-blox chip to have the PPS on the DCD/CLK pin of the CH341A.

My software:
I am using ntp 4.2.8p15 on windows with loopback-ppsapi-provider.dll drivers

Here is my ntp.conf:

server ntp.lothaire.net minpoll 4 maxpoll 6
server ntp-p1.obspm.fr minpoll 4 maxpoll 6
server 127.127.20.14 minpoll 4 maxpoll 4 mode 16 prefer
fudge 127.127.20.14 refid NMEA
server 127.127.22.14 minpoll 4 maxpoll 4 true
fudge 127.127.22.14 refid PPS
tos mindist 0.5

I let it run for a while, and this is what I get:

C:\Users\toto>ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
*GPS_NMEA(14) .NMEA. 0 l 3 16 377 0.000 -62.580 2.642
oPPS(14) .PPS. 0 l 11 16 377 0.000 -0.252 0.539
+arcturus.ciril. 193.50.27.139 2 u 15 16 377 37.707 +110.85 0.195
+ntp-p1.obspm.fr .MRS. 1 u 14 16 377 33.250 +110.44 11.592

Subject	Author
GPS+PPS vs NTP server, why such a large offset ?	Thibaut HUMBERT