[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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