ebay u-blox LEA-6T GPS module teardown and initial test

[texaspyro]

Thats pretty much what a timing receiver does.  With a known fixed position, it can also output time solutions with just one satellite in view.   Timing mode receivers can also operate without a fixed location.  The firmware may have tweaks to optimize the GPS solutions for improved time accuracy at the expense of position.  Timing firmware may have a message that sends 1PPS output sawtooth error corrections that normal firmware does not have.

With the proper firmware any GPS receiver can be a timing receiver... its just that the receiver makers tend to double the price for timing firmware.  Ublox configures their receivers so you can't load timing firmware on modules that were not originally sold as timing receivers.

[mark03]

Right, so the claim several posts back about the non-8T modules being essentially the same as the 8T modules, except you have to query for sawtooth data instead of having it spit out automatically, is incorrect.  That's what I was attempting to clarify.

[texaspyro]

Most of the Ublox messages can be configured to be output at a specified interval.  The "T" versions might default to being output... I don't know for sure if they are.

[cdev]

Does the output of ntpq serve any useful purpose? This is my non-timing receiver currently sitting on my living room coffee table with an indoor passive antenna.  Is the clock jitter low or is that not the meaningful figure. Its taken a while to tweak the settings to get it this low but then again, as I dont really understand what the numbers mean, I could be making mistakes and I would never know..

I have no idea what the settings mean. The documentation isnt very helpful at all.

I wish the NTP documentation was better. It would be a golden opportunity to teach people all sorts of interesting things.

ntpq -c rv -c pe -c cv -c kern -c as
associd=0 status=0415 leap_none, sync_uhf_radio, 1 event, clock_sync,
version="ntpd 4.2.8p10@1.3728 Fri Jul 14 05:12:26 UTC 2017 (1)",
processor="armv6l", system="Linux/4.1.19+", leap=00, stratum=1,
precision=-19, rootdelay=0.000, rootdisp=450.030, refid=GPS,
reftime=dde3060d.0e333675  Mon, Dec 18 2017 22:29:17.055,
clock=dde30610.07937c4a  Mon, Dec 18 2017 22:29:20.029, peer=33092, tc=3,
mintc=3, offset=0.000651, frequency=-35.014, sys_jitter=0.001907,
clk_jitter=0.002, clk_wander=0.000, tai=37, leapsec=201701010000,
expire=201806280000
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
oGPS_NMEA(0)     .GPS.            0 l    3    8  377    0.000    0.001   0.002
+clock.nyc.he.ne .CDMA.           1 u    1   16  377   13.832    3.419   1.643

XXXXXXXXXXXXXX
seven servers omitted for brevity
XXXXXXXXXXXXXX


-time-a-g.nist.g .NIST.           1 u   15   32  377   42.130   -6.978   6.841
associd=0 status=0062 6 events, clk_bad_format,
device="NMEA GPS Clock",
timecode="$GPGGA,032920.000,____.____,N,_____.____,W,1,10,1.1,94.0,M,-34.3,M,,0000*__",
poll=10786, noreply=0, badformat=6, baddata=0, fudgetime2=150.000,
stratum=0, refid=GPS, flags=9
associd=0 status=0415 leap_none, sync_uhf_radio, 1 event, clock_sync,
pll offset:            0.000591
pll frequency:         -35.0139
maximum error:         0.4515
estimated error:       1e-06
kernel status:         pll nano
pll time constant:     3
precision:             1e-06
frequency tolerance:   500
pps frequency:         0
pps stability:         0
pps jitter:            0
calibration interval   0
calibration cycles:    0
jitter exceeded:       0
stability exceeded:    0
calibration errors:    0

ind assid status  conf reach auth condition  last_event cnt
===========================================================
  1 33092  971b   yes   yes  none  pps.peer clock_alarm  1
  2 33093  941d   yes   yes  none candidate              1
  3 33094  9414   yes   yes  none candidate   reachable  1
  4 33095  9314   yes   yes  none   outlier   reachable  1
  5 33096  9314   yes   yes  none   outlier   reachable  1
  6 33097  9314   yes   yes  none   outlier   reachable  1
  7 33098  9414   yes   yes  none candidate   reachable  1
  8 33099  9414   yes   yes  none candidate   reachable  1
  9 33100  9314   yes   yes  none   outlier   reachable  1
 10 33101  9314   yes   yes  none   outlier   reachable  1

[Leo Bodnar]

Have you ever measured the stability/jitter of its 1KHz ouput?

Everything that runs on Ublox chip is clocked from 48MHz system clock, inlcuding both timepulse outputs.  Thus +-10.4ns quantisation which is just the nearest 20.83ns clock.  Ublox is basically Cortex-M3 with RF bodged onto it.

Leo

[cdev]

So Ublox is really not so different than Skytraq which uses a Leon processor (a SPARC core originally designed for the EU space effort) but I think Skytraq has around an 80 MHz clock