I took a trip to visit the folks over Thanksgiving and thought I would share some observations on GPS antenna location.

I have a Garmin Etrex Vista GPS that doesn't have an external antenna. I have been using a re-radiating antenna with the receiving antenna mounted in the center of the dash up over the defroster outlets in my 2k 4R. This unit has a small pencil-shaped antenna you mount near the GPS so the GPS itself doesn't have to "see" the sky to pick up the satellites.

I've always thought that reception wasn't any too great and as I was driving East of Seattle on I-90, the signal kept dropping out, even with the GPS itself on the dash. It was bad enough that going through the Cascades to Snoqualmie Pass, it was out more than in, and this isn't like being at the bottom of the Grand Canyon either. I finally stopped at a rest area and ran the wire out the passenger door window and tied the antenna to the roof rack.

It made a big difference! By the time I made the change, I was out of the mountains, but through the generally flat country in central Washington and down into Oregon, I was getting 11 or 12 satellites. The most I remember ever seeing before was 8. On the way home where I was having so much trouble before, I don't think I ever had less than 5 satellites being received.

Now I've got to figure out a way to route the cable so I can make a permanent mount on the roof, as this is a big improvement. Routing the wires will be a bit of a challenge because the antenna comes all connected with the receiver, a cig. lighter power supply, and the re-radiating antenna (like a thin pencil about 4" long) all wired together. I suspect the cable to the antenna is a coax cable so cutting it up is not an option. Making a bracket to fix the receiving antenna to the factory rack rails will be easy enough if I can get the wire there.

The Vista is set up to work the the Wide Area Augmentation System (WAAS) satellites that the FAA has for airplane navigation (experimental at this point) and I was picking one of them up too for the first time. There are only two of the WAAS satellites and they are low on the horizons off the E and W coast so they don't come in super reliably, especially as you go inland. When I was receiving it, the GPS was reporting 7 or 8 foot accuracy.

I was using ExpertGPS on a laptop and tracking against satellite photos for a moving map display most of the 500 mile trip back home and it appeared to be real accurate the whole way with no dropouts.

The only drawbacks I see right now are that the ExpertGPS program seems to have a few hickups. Once it had a portion of the display that was "stuck" and wasn't updating with the new photos. Another time it wasn't updating the satellite status to show which ones were received (compated to the GPS itself). It froze up completely one other time too.

Alan

 

Which antenna are you using? I'm ready to put my Etrex Legend on Ebay because it doesnt work worth a darn back in the woods. Even when there is clear sky directly above me, it still cuts out. Doesnt do much good this way.

 

Adam,

I was disappointed with the performance in trees too. Going down a logging road with tall trees on the sides caused lots of signal loss. I won't know how much improvement moving the antenna makes there until I get a chance to experiment more. I certainly see an improvement, but whether it solves all the problems I don't know.

I have a Big Brother re-radiating antenna. It was made by these people http://www.tri-m.com . It looks like they have discontinued it, but there is another one listed that might work. Don't know if there are others.

They're fairly expensive, so it will cost a few bucks to even experiment. I suppose you could find a spot where reception is bad (assuming this is in your rig) and try putting the GPS on the roof or at least ouside the vehicle to see if that helps. There seems to be an ongoing debate about the Etrex antenna sensitivity, but I'm not sure if there is a consensus yet or if you'd be better off to just get another unit with the external antenna.

It wasn't my original plan, but I've been using my GPS with a PC and have considered just getting a really "dumb" GPS with the serial or USB output and no display for a permanent setup. I find it kind of a pain to have to switch the GPS on all of the time and I don't make use of all the Vista features for in-car navigation. The Expert GPS PC software (and I think other sw packages probably do to) displays speed, altitude, compass bearing, satellite signal strength and time, and can record tracks and display them so I don't think I even really need to see the GPS itself. If you are considering PC navigation, I'd give that some thought before sinking another hundred bucks into an active antenna. (I haven't tried Ebay to see if there are any for sale cheap.)

I really want a GPS with a dead reckoning unit built in to deal with signal loss. These have a gyro or accelerometers and a hookup to the speedo and reverse switch (at least some) to determine a position when the GPS drops out. They can help a lot in cities with tall buildings, tunnels, etc. and should help with tree cover too unless the bumping around of rough roads throws the gyro off too bad. Most of the high-end dedicated units have gyros or similar, but I'm kind of a do-it-yourselfer and like the flexibility of the PC/GPS combo.

I even checked with an Australian company that makes a unit with GPS and a gyro system. The signal output is the standard NMEA format if I remember right so you could use it with most of the PC software. Unfortunately, they wanted something like $1500.00 for it. I saw at least one other maker of something similar, but I doubt its any cheaper.

I've seen a GPS receiver/dead reckoning piece of the Alpine navigation unit advertised for something in the $3-$400 range if I remember right, but haven't seen enough info to tell if this would work on anything but the Alpine system.

Hope this helps.

Alan

 

hey how much will you be selling it for? i wanted to pick up a etrex legend. would u sell it to me?

 

I'm glad to know that you get better accuracy with another antenna. The best I ever got with the Etrex Vista was 11feet, and I was practically pointing the unit at the ground, so go figure. I want to get the gpsmap 176 and an external antenna, I think this will be a good setup.

Adam - I used the Etrex Vista at the 4runner jambo back in June and it worked pretty well in the woods of GWNF, so I don't really know what to say about reception. The external antenna must do something good though.

 

I can get about $150 on ebay for it. It comes with the auto adapter too. I'd sell it to anyone who has the money!! It still is under warranty untill january 1st!!