[time-nuts] GPS receiver time message offsets to 1PPS (updated)

Bob Camp kb8tq at n1k.org
Thu Jul 28 07:07:05 EDT 2016


Hi

So everything is inside a 10 ms sdev except:

UBLOX LEA-6T NMEA at 11.1 ms (Binary is much better) 
Adafruit Ultimate at 39.8 ms

Neither one of those are really surprising. NMEA is not the best thing on uBlox.
The specs on the Adafruit part have never made much sense for timing. Somebody
was a bit confused when they did (or at least spec’d)  that part. 

There is the Skylab SKM53 at 37.8 ms. I’ve never seen one of those, so no guess
about that one. 

The surprise in the crowd is the Res-T SMT at 63.7 ms. I wonder what they messed
up? 

Bob


> On Jul 27, 2016, at 10:13 PM, Mark Sims <holrum at hotmail.com> wrote:
> 
> I found what was causing the apparent ramps in the message offset time for the Motorola mode receivers and the Z38xx receivers.  Here is the updated and corrected info.  Note that a couple of receivers do have some minor ramp sawtooths in their message timing.  They are less than +/- 10 msecs from nominal.
> 
> -------------------------------------------  
> 
> 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 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 and baud rate) these measurements are of the last byte of the message.  This was chosen to assist people trying to sync a clock to a GPS receiver without relying on the 1PPS pulse.  They are also useful to people that want to knowhow long they have to process a timing message (like to set a sawtooth compensation delay line) before the next 1PPS pulse comes out.
> 
> 
> A few receivers appear to not fully sync their timing message to some referenceclock.  This causes the timing message arrival time to follow a ramp curve.The ramp size is fairly small (+/- 5 to 10 msecs) in most receivers.
> 
> 
> 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              -287.9      3.2 
> Jupiter Pico    Zodiac        14.00 11/28/05    -1235.5      0.4  (ramps -1225 .. -1245 over 130 minutes)
> Jupiter Pico    Motorola      14.00 11/28/05     -298.0      1.8 
> 
> Motorola UT+    Motorola      R5122U1112         -258.2      3.7 
> Synergy M12+    Motorola      P273T12T11         -194.8      1.4  
> 
> Z3812A          SCPI          X98-4-A             949.5      0.8  (ramps 945 .. 955 over 16 seconds)
> Z3801A          SCPI 19.2K    3543A               973.0      2.0
> 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 
> 
> 		 	   		  
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.



More information about the time-nuts mailing list