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How about a GPS receiver for Big Trucks?...
Ken in Regina
Have you checked a magnet mount CB or Ham radio antenna? They are constructed the same way .. no ground plane and you don't scratch the paint on your car to get a physical connection to the metal. The connection with the ground plane is made via the magnet.

If you don't believe me, get a magnet mount CB antenna and a CB radio with a good meter on it. Set the magnet mount antenna on a piece of wood or plastic somewhere away from any metal and see what sort of reception you get. Now stick it on the roof of the car and see the difference. To test further, hook an SWR (standing wave ratio) meter inline with the antenna and check the SWR with the mic keyed, both off the metal and on the metal.

For a test with your magnet mount GPS antenna, try using a small cast iron or stainless steel frying pan inside the house. Find a place in the house where the signals are hard to get with the antenna by itself, then stick it to a piece of (ferrous) metal 4" or so in diameter or larger.

If you never have reception problems it's not an issue. I simply mentioned it in my original comment that it's a bonus. With the adapter that was mentioned you not only get a good place to stick a magnet mount GPS antenna; you also get a good ground plane. In locations with more difficult reception it will be helpful. If you never go such places, it's still a good mounting point for use on the truck. Win-Win.

...ken...
OTR
I mounted a US Globalsat MR-350 on a pole. I used pipe fittings and some sythetic wood called Starboard. I fixed that rig to the out side of my mirror on my truck. I used SS hose clamps for that. I ran the wire for the GPS down through the pipe. OTR
tcassidy
I don't believe a seperate ground plane is as important for a GPS antenna because of their design and the lack of a whip. More important is a clear view of the sky in as many directions as possible.

Terry
Ken in Regina
Quote:
Originally Posted by tcassidy
I don't believe a seperate ground plane is as important for a GPS antenna because of their design and the lack of a whip. More important is a clear view of the sky in as many directions as possible.

Terry
But that's just the point, Terry. Sometimes you don't have a clear view of the sky in all directions.

Out here on the Canadian Prairies it's pretty wide open so I'm in the habit of just tossing my external antenna on the dash inside the front window and that works fine most of the time. ... Until I drive the TransCanada Hiway through places like Three Valley Gap, completely surrounded by high mountains. On the dash I lose the lock. But if I put it on the roof so it gets a good ground plane I'm able to get just enough signal for a 2D lock. There are lots of other places in the Rockies where I need to do that.

...ken...
tcassidy
Ken,
I'm not sure that is proof of ground plane (as in a large piece of metal) as it is in better sky view. On the roof the antenna can see in a 360 degree sweep. On the dash, it can only see maybe 120 degrees. Plus there is less interference in its way such as the windsheild.

Terry
Ken in Regina
Quote:
Originally Posted by tcassidy
Ken,
I'm not sure that is proof of ground plane (as in a large piece of metal) as it is in better sky view. On the roof the antenna can see in a 360 degree sweep. On the dash, it can only see maybe 120 degrees. Plus there is less interference in its way such as the windsheild.

Terry
Yes, I thought of that and tested to see how much difference it made. I have a piece of galvanized metal (the surplus side from a modular electrical box left over from when I wired my workshop) that is about 4" square. I use it as the mounting point for my external antenna when I use the GPS with my golf cart (my GPS/PDA has a Golf program on it that tells me my yardages). On one trip in the mountains when I was in the boonies with mountains and tall evergreens all around and the lock was lost I pulled the plate from my golf cart (my golf clubs are like your dogs, I never leave home without them) and stuck it under the antenna on the dash. That got a 2D lock back. The signal strength was a bit weaker than when I put the antenna up on the roof, for all the reasons you mentioned, but just having the ground plane made it quite usable.

Any time I put the antenna on the dash with that galvanized plate under it the signal strength is noticeably greater than without it. Most of the time it's a non-issue for me because the signal strength out here on the Prairies is excellent all the time. It's just nice to know that I can improve the reception when I need to with such a simple remedy. And it's not always the answer because you can get into some places that it's impossible to get GPS signals no matter what you try.

...ken...
Marvin Hlavac
I'd like to add here, for the benefit of readers, an excerpt from Wikipedia.org regarding what ground plane is:

Quote:
In telecommunication, a ground plane structure or relationship exists between the antenna and another object, where the only structure of the object is a structure which permits the antenna to function as such (e.g., forms a reflector or director for an antenna). This sometimes serves as the near-field reflection point for an antenna.
Source: http://en.wikipedia.org/wiki/Ground_plane

"Ground plane" doesn't necessarily have to be "grounded" or connected with an electrical wire to anything (although it may be). "Ground plane" is simply a piece of metal, or a wire, or wires, usually placed bellow certain types of antennas. The relationship between the actual antenna and the "ground plane" improves the efectivness of the antenna.
OTR
I am not sure why I got a reply to what I posted. I did not mentions ground plain, just a method I used to mount a GPS modual. Please let me know if I am missing something. OTR.
OTR
Please excuse my confusion, I just signed up on this forum a day or two ago. If I should have responded to a post and did not I am sorry. OTR
Ken in Regina
Quote:
Originally Posted by OTR
Please excuse my confusion, I just signed up on this forum a day or two ago. If I should have responded to a post and did not I am sorry. OTR
Not to worry, OTR. The ground plane part of the discussion spun off from someone else's message in this thread. If you look back a ways in the thread you will see that it began before your message was posted and just happened to continue after your message. Once you get a little more experience in reading these discussions you will discover that sometimes they will take on a life of their own.

Welcome aboard.

...ken...
OTR
OKee Dokee, Thanks
Marvin Hlavac


OTR, you are the first person I've met who uses US Globalsat MR-350! How is it? How do you like it? I think I would likely get one too if I were to drive a big rig, or if I didn't mind drilling a hole in my roof, or if I wasn't lazy creating an appropriate mounting solution for it.

Perhaps even the antenna inside GlobalSat MR-350 is a bit larger than antennas in other GPS receivers. The diameter of the unit is 62mm, and for example the diameter of the popular BU-353 is only 53mm. A larger antenna would mean better performance.
OTR
We have had no problems with the MR-350 to date. We have been running with it for about 18 months. The only issues we are having with GPS now are software related. If you decide you want to mount it on your mirrors let me know and I will take a picture or two of the mounting pole I made.
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