[time-nuts] GPS Antenna

Miguel Gonçalves mail at miguelgoncalves.com
Mon Sep 12 14:13:38 UTC 2011


Hi all!

First let me introduce myself: I am a time nut since 1996 (former admin of a
stratum 2 server: bug.fe.up.pt) but college and other priorities kept me
away from my obsession.

The other day I happened to buy a Garmin 18 LVC unit and installed it in the
roof in my company. It has been working great and it handled the hot days of
August quite well. It shares it's time with the entire network through NTP.
Here it is:

tick# ntpq -pn
     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
*127.127.20.0    .GPS.            0 l    1   16  377    0.000    0.010
0.004
 10.0.2.9        .GPS.            1 u    4   16  377    0.161    0.012
0.007
 194.117.9.130   194.117.9.129    2 u   33   64  377   14.810    1.154
0.886
 194.117.9.136   194.117.9.138    2 u   62   64  377   14.307   -2.253
3.324
 193.136.5.7     193.136.250.246  2 u   18   64  377   11.719    1.549
0.811
 193.136.5.15    193.136.250.246  2 u   43   64  377   15.922    1.166
0.819
 178.79.160.159  217.20.44.6      2 u   51   64  377   43.315   -0.816
0.666

BTW, it's an embedded machine (ALIX 1D) running FreeBSD 7.4 out of a Compact
Flash card. I am looking at other stratum 2 servers to see if my time is
off.

I also added another stratum 1 server (tock, 10.0.2.9) using the same
FreeBSD/CF configuration but on a more powerful machine (an old server
laying around). This time I used a Sure GPS Evaluation Board. Here it is:

tock# ntpq -pn
     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
o127.127.20.0    .GPS.            0 l    6   16  377    0.000   -0.009
0.001
 10.0.2.10       .GPS.            1 u    3   16  377    0.176   -0.015
0.004
 194.117.9.130   194.117.9.138    2 u   29   64  377   14.458    0.837
2.336
 194.117.9.136   194.117.9.138    2 u   22   64  377   14.073   -2.361
2.371
 193.136.5.7     193.136.250.246  2 u   20   64  377   12.425    1.420
0.377
 193.136.5.15    193.136.250.246  2 u   26   64  377   16.594    1.651
0.924
 178.79.160.159  217.20.44.6      2 u   23   64  377   44.289   -0.722
1.819

I've also installed, at home, a FreeBSD machine (same software as before)
but this time I hooked it with a Motorola Oncore UT+ (great unit by the way)
and configured it to resolve only time (averaged the antenna location for 24
hours). This machine is also running NTP:

oncore# ntpq -p
     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
oGPS_ONCORE(0)   .GPS.            0 l   12   16  377    0.000    0.002
0.001
 canon.inria.fr  .GPSi.           1 u   30   64  377   56.218    3.469
0.261
 ptbtime1.ptb.de .PTB.            1 u   23   64  377   65.395    0.225
0.355
 ntp.inrim.it    .CTD.            1 u    7   64  377   50.840    0.185
0.314
 ntp02.oal.ul.pt 194.117.9.138    2 u   61   64  377   10.703   -0.811
2.863
 ntp04.oal.ul.pt 194.117.9.138    2 u   46   64  377   10.361   -3.673
0.401
 Router7.Lisboa. 193.136.250.246  2 u   17   64  377    8.313   -0.189
0.390
 Router15.Porto. 193.136.250.246  2 u   65   64  377   13.052    0.040
0.280
 li298-159.membe 217.20.44.6      2 u   64   64  377   40.719   -2.208
0.385

The Oncore machine has the antenna indoors (near the window) and after
looking at the clockstats file I have this

oncore# /var/tmp/sats.sh
8 satellites:        0
7 satellites:        0
6 satellites:      870
5 satellites:     7941
4 satellites:     7313
3 satellites:     6385
2 satellites:      575
1 satellites:        0

The machine has been running for 6 hours and it has been seeing a good
number of satellites for most of the time.

Do you think I should buy an external antenna like this one:
http://www.ebay.co.uk/itm/Panasonic-NAis-VIC-100-TNC-Timing-GPS-L1-Active-Antenna-/180721168817?pt=LH_DefaultDomain_0&hash=item2a13d231b1or
my current antenna (
http://www.ebay.co.uk/itm/ws/eBayISAPI.dll?ViewItem&item=330464866792) is
good enough used indoors?

Thanks for your help.

Cheers,
Miguel


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