Here are the results of measuring the difference between the time code in a GPS
receiver time message and the arrival time of the last byte of the message.
Negative values mean that the receiver sends the timing message after the 1PPS
pulse that it describes. The table also shows the standard deviation of the
message arrival times.
The test configuration was a Compaq N610C laptop (2 GHz Pentium, hardware
serial port) running Linux Ubuntu Mate 15.10). The time of the messagearrival
was from the system clock synced to NTP. The receivers were tested in native
binary protocol and, if supported, NMEA. The com port was runningat the
default value for the receiver. If not specified that was 9600:8:N:1Data was
collected after the receiver had been tracking satellites for at least 1 hour
and averaged over 4 hours. The timings were also checked andagree with those
on a 1.2 GHz Raspberry PI 3 and a quad-core 3 GHz box.
Although measuring the arrival time of the first byte of the timing
messagemakes more technical sense (less variation due to timing message length)
thesemeasurements are of the last byte of the message. This was chosen to
assistpeople trying to sync a clock to a GPS receiver without relying on the
1PPSpulse. They are also useful to people that want to know how long they
haveto process a timing message (like to set a sawtooth compensation delay
line) before the next 1PPS pulse comes out.
Several receivers appear to not sync their timing message to some
referenceclock. This causes the timing message arrival time to follow a ramp
curve.
Device Protocol Firmware (msg-arrival) sdev
(msecs)
============= ===== ================ ======== =====
Thunderbolt TSIP App:3.0 GPS:10.2 -52.9 6.2 (gold box)
Thunderbolt TSIP App:2.22 GPS:10.2 -67.2 10.2 (red box)
Resolution-T TSIP GPS:1.26 -140.0 5.4
Res-T SMT TSIP GPS 2.7 -475.0 63.7
Starloc II TSIP App:1.10 GPS:1.2 -267.5 7.2
Trimble NTWx? TSIP GPS 10.4 -44.9 1.2
Nortel NTPx TSIP GPS 10.1 -61.8 1.4
Nortel NTGx TSIP GPS 10.5 -57.2 2.4
Ublox LEA-6T binary 6.02 (36023) -242.7 4.4
Ublox LEA-6T NMEA 6.02 (36023) -198.7 11.1
Ublox Neo6M binary 7.03 (45969) -211.6 9.3
Ublox Neo6M NMEA 7.03 (45969) -149.0 8.4
Ublox 7 binary 1.00 (59842) -186.9 2.6
Ublox 7 NMEA 1.00 (59842) -152.9 7.9
Ublox NEO-8M binary 2.01 (75350) -192.7 9.1
Ublox NEO-8M NMEA 2.01 (75250) -182.4 8.0
V.KEL SIRFIII binary GSW3.2.5 -432.8 6.1
V.KEL SIRFIII NMEA GSW3.2.5 -427.6 5.0
Navspark Mini Venus8 1.7.27 15.8.18 -139.3 7.1
Adafruit Ultimate NMEA -428.2 39.8
Skylab SKM53 NMEA -492.0 37.8 (has short
jumps to usually -180)
Jupiter-T Zodiac 93.07 -1263.6 3.3
Juptier-T Motorola 93.07 -774.5 4.7 (ramps -274
.. -1274 over 1000 secs)
Jupiter Pico Zodiac 14.00 11/28/05 -1236.9 0.4 (ramps -1225
.. -1245 over 130 minutes)
Jupiter Pico Motorola 14.00 11/28/05 -771.0 4.7 (ramps -1271
.. -271 over 1000 secs)
Motorola UT+ Motorola R5122U1112 250.5 5.0 (ramps -250
.. +750 over 900 seconds)
Synergy M12+ Motorola P273T12T11 300.5 1.1 (ramps -200
.. +800 over 1000 seconds)
Z3812A SCPI X98-4-A 1450.5 0.6 (ramps 950 ..
1950 over 1000 secs)
Z3801A SCPI 19.2K 3543A 1341.5 2.0 (ramps 941 ..
1841 over 1000 secs)
Symmetricom UCCM-P 57.6K 1.0.0.2-01 -115.5 3.6 (ramps -109
.. -119 over 10 seconds)
Trimble UCCM 57.6K 3.0.0.11-0 -278.5 3.1
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