Article 44920 of sci.geo.satellite-nav: Path: matra.meer.net!news1.best.com!su-news-hub1.bbnplanet.com!cpk-news-hub1.bbnplanet.com!news.bbnplanet.com!news-peer.sprintlink.net!news-pull.sprintlink.net!news-in-east.sprintlink.net!news.sprintlink.net!Sprint!207.67.253.7!atmnet.net!vigra.com!news.vigra.com!steve From: steve@vigra.com (Steve Haehnichen) Newsgroups: sci.geo.satellite-nav Subject: Lowe Electronics GPS antenna vs. Garmin GPS-II+ stock antenna Date: Mon, 25 Aug 1997 04:58:34 GMT Organization: Vigra - VisiCom Labs, Inc. San Diego, CA Lines: 99 Message-ID: Reply-To: steve@vigra.com NNTP-Posting-Host: 199.254.9.2 Xref: matra.meer.net sci.geo.satellite-nav:44920 I recently received my Lowe Electronics magnetic mini-antenna, and was curious to see how it would compare to my Garmin GPS-II+ standard antenna, so I ran a few quick tests. I don't claim that these results are "standard", or statistically significant, but they tell me what I wanted to know. POWER CONSUMPTION: I do most of my GPS tracking from internal batteries, so the long run-time of the GPS-II+ is important to me. I was concerned that the Lowe antenna (or any active external antenna) would put a large dent in the battery life. Fortunately, this does not appear to be the case. The GPS-II+ with factory antenna draws approx 95mA from the batteries. (The current draw is rather pulsed, so it's hard for me to measure accurately.) This is in-line with the 24-hour run time and Duracell's 2850 mA/hr rating for the AA cell. With the Lowe mini Antenna attached, the Garmin GPS-II+ draws 113-129mA (pulsed), averaging around 120mA, from what I can tell. For my needs, this is very good! I get better receiver performance and flexible GPS antenna placement for a 20% reduction in battery life. All things being linear, I should expect 19 hours of run time with the Lowe antenna. (I have been getting *better* than Garmin's stated battery life in the past.) From the external power input to the GPS, I get 50mA @ 12v consumption with the factory antenna, and 60mA @ 12v with the Lowe antenna. Exactly the same 20% increase. (This all reflects very well on the Garmin internal DC/DC power convertor, BTW.) As an aside, my Lowe antenna draws 21.3 mA at 5.00v DC, much less than its rated max power spec of 32 mA. According to data posted by Lowe (Richard Mclachlan), current draw from the last production run varies from sample to sample within "14.2 to 20.9 mA", so it looks like I got one on the high end. :-( PERFORMANCE: To try to quantify the performance differences, I ran the "SA Watch" program from S.R. Huntting (http://www.mutadv.com/kawin). I logged ten hours of fixes using the factory antenna, and then another ten on the Lowe antenna. The test environment was "difficult"; much more so than my normal applications. Specifically, the antennae were tested at exactly the same place on top of my indoor wooden storage cabinet. For comparison, the GPS-38 can not get a fix at all, and the Trimble Accutime has trouble holding it. Unfortunately, SA Watch doesn't seem to be able to export or print the statistics(?!), so I can only manually quote a few here: GPS-II+ with FACTORY ANTENNA: Elapsed time: 0:10:29:56 - Logging time: 0:10:29:56 for 18,699 records Minimum Maximum Mean EPE 16.1 60.9 26.91 HDOP 1.0 6.4 1.92 SVs Tracking 3 8 5.67 2D Position std. deviation: 46.99m GPS-II+ with LOWE MINI GPS ANTENNA: Elapsed time: 0:10:05:19 - Logging time: 0:10:05:19 for 18,047 records Minimum Maximum Mean EPE 15.2 55.8 23.35 HDOP 0.9 5.0 1.69 SVs Tracking 3 9 6.18 2D Position std. deviation: 37.33m Before you statisticians get all excited and warm up the flamethrowers, I KNOW this is not reliable data. Most significantly, I could have picked two different time periods with widely different satellite coverage and biased the results. I believe that 10 hours is barely adequate to get an idea of what to expect, but it was intersting to see. On average, the Lowe antenna tracked "half an SV" :-) more than the factory antenna. This is good! The extra SVs are probably what gave it the edge in the HDOP and reduced the 2D std. dev by almost 10m, or 20 percent! I intend to collect more data, of course, but these early results confirm what I suspected from watching the signal bars. The Lowe antenna pulls in signals much better than the factory antenna. The fact that it can be placed remotely to the GPS is even more beneficial to my applications, but it's good to know that it's also a superior antenna. Again, I have no personal or business connection with Lowe. I just bought one from them at http://www.lowe.co.uk/gpsant.html, and so far, I'm quite pleased! -Steve Steve Haehnichen Vigra, a division of VisiCom Labs. steve@vigra.com (619) 597-7080 x169 Fax: (619) 597-7094 (800) 668-4472 San Diego, CA Article 46009 of sci.geo.satellite-nav: Path: matra.meer.net!news1.best.com!nntprelay.mathworks.com!howland.erols.net!newsxfer3.itd.umich.edu!nntp.cs.ubc.ca!cs.ubc.ca!cs.ubc.ca!not-for-mail From: davem@cs.ubc.ca (Dave Martindale) Newsgroups: sci.geo.satellite-nav Subject: Re: Lowe Antenna for G-12XL Date: 8 Sep 1997 23:11:00 -0700 Organization: Computer Science, University of B.C., Vancouver, B.C., Canada Lines: 37 Message-ID: <5v2p9k$g70@harpo.cs.ubc.ca> References: <01bcbc74$638b40f0$fe011d0a@netadmin> NNTP-Posting-Host: harpo.cs.ubc.ca Xref: matra.meer.net sci.geo.satellite-nav:46009 "Jason Durbin" writes: >The info I've seen thus far is company specs on the antenna, but I'd like >to hear from someone that's currently using one. How do you like the >quality? Any noticeable improvement/degradation in signal strength with >and without the Lowe antenna at a common location? Any other comments? With a clear view of the sky, the Lowe antenna gives nearly full-height signal bars on almost all satellites. This is a marked improvement over what you get with the passive antennas that come with the Garmin GPSes. It makes a substantial difference in speed of acquisition and ability to track even in the clear on the older single-channel receivers like the 45 XL. The newer parallel receivers (12XL, 12, II+) do pretty well with their internal antenna with a clear sky view, so the difference when adding an amplified antenna is not so noticeable with them. But in poor signal conditions like in a forest, an amplified antenna like the Lowe can make the difference between a fix and no fix. The Garmin GA-26 and GA-27 are also amplified antennas. When attached directly to the GPS, the Lowe, the Trimble "Miniature OEM antenna", and the Garmin units all work about the same. The Garmins draw less battery power than the Lowe and Trimble (about 15 mA vs. 25 mA) but are physically larger. The Lowe and Trimble antenna preamps have more gain than the Garmin units. This doesn't help any when connected directly to the GPS, since then it's noise figure that matters, not gain. But you can use a *long* piece of coax between the Lowe/Trimble and the GPS if you need it. I've had about 75 feet of cable (15 feet of RG-174 that comes with the antenna plus 60 feet of RG-58) between the antenna and GPS, and still had good signal strength. You'd want to use a bit shorter maximum length with the Garmin antennas. On the other hand, the lower gain of the Garmin antennas should give less problem with intermodulation effects in RF-rich environments. In practice, I haven't seen this myself. Dave