[ntp:questions] garmin 18x and linux

Miguel Gonçalves mail at miguelgoncalves.com
Wed Sep 7 00:03:31 UTC 2011


On 6 September 2011 23:02, Chris Albertson <albertson.chris at gmail.com>wrote:

> > Why don't the manufacturers provide the PPS signal to the serial port
> > themselves? Is it meant to be NMEA only?
>
> If cost is an issue there are even lower priced options then the one
> from Sure Electronics.   Older Moterola UT+ receivers sell for $18.
> These actually have better specs and the signals are all run out to a
> 10-pin header, no soldering.
>

I second this. I am looking at a Motorola Oncore UT+ unit I got on ebay for
about 10 USD. I believe the antenna cost me 7 USD. :-)

A quick trip to the local electronics shop and with a bit of soldering I
have a board that gets the power from USB and returns the GPS signals to
NTP. Oncore is connected to this board by a flat 10 wire cable. Quite neat!
:-)

The performance is quite impressive:

oncore# uptime; ntpq -p; ntpdc -c kerninfo
12:02AM  up  2:07, 1 user, load averages: 0.00, 0.00, 0.00
     remote           refid      st t when poll reach   delay   offset
 jitter
==============================================================================
oGPS_ONCORE(0)   .GPS.            0 l    7   16  377    0.000   -0.001
0.001
 canon.inria.fr  .GPSi.           1 u   34   64  377   49.054    0.621
0.383
 ptbtime1.ptb.de .PTB.            1 u   36   64  377   66.475    0.864
0.316
 ntp.ien.it      .CTD.            1 u    6   64  377   52.064    0.452
0.263
 ntp02.oal.ul.pt 194.117.9.138    2 u   27   64  377    9.486    0.565
0.453
 ntp04.oal.ul.pt 194.117.9.138    2 u   34   64  377   10.109   -0.831
0.235
 Router7.Lisboa. 193.136.250.246  2 u   27   64  377    8.181    0.508
0.258
 Router15.Porto. 193.136.250.246  2 u   13   64  377   12.538    0.528
0.129
pll offset:           -8.37e-07 s
pll frequency:        -32.057 ppm
maximum error:        0.004234 s
estimated error:      1e-06 s
status:               2107  pll ppsfreq ppstime ppssignal nano
pll time constant:    4
precision:            1e-09 s
frequency tolerance:  496 ppm
pps frequency:        -32.057 ppm
pps stability:        0.016 ppm
pps jitter:           1.811e-06 s
calibration interval: 256 s
calibration cycles:   50
jitter exceeded:      5
stability exceeded:   0
calibration errors:   3

I've tried Garmin 18 LVC and Sure. Not want to start a war here but for the
specifications and price Oncore beats both. :-)

Just my 2c.

Cheers,
Miguel



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