Ground Independent Antennas Question

Submitted: Monday, May 09, 2005 at 16:43
ThreadID: 22813 Views:5577 Replies:8 FollowUps:4
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Okay just a question about antennas. When an antenna is ground independent, they can be mounted on a pole or non metal surface. When they aren't, they have to be mounted on a ground plane, such as a metal roof. My question is can a ground independant antenna be mounted onto a metal surface also just like the others or only on a pole like they're supposed to? I'm thinking of purchasing an antenna but it is ground independant and I don't need it to be. Should this be okay or can only the non ground independant antennas be mounted on the roof? Help please!
Thanks
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Reply By: Wayne (NSW) - Monday, May 09, 2005 at 16:56

Monday, May 09, 2005 at 16:56
Big Bazza,

The way I understand it about antennas is that, the best position for any antenna is in the middle of the roof of the vehicle.

If you have a ground plane independent antenna it can go almost any where. The bull bar does not have a large surface but a GPI antenna will still work.

If you are getting a new antenna get a GPI one, and it will go almost any where on the vehicle as long as it is up high enough to clear the roof line on the vehicle.

Wayne
AnswerID: 110480

Reply By: hl - Monday, May 09, 2005 at 16:56

Monday, May 09, 2005 at 16:56
Hi,

Yes, that will be fine. You can mount it anywhere.

Cheers
AnswerID: 110481

Reply By: Member - Banjo (SA) - Monday, May 09, 2005 at 17:16

Monday, May 09, 2005 at 17:16
Indeed....so called (maybe true) exerts advised me that a good GPI job needs only be as high as you can get it, so that it can have a good "look" at other mobiles etc. - gutter or roofrack - either is good. Mine is still down on the bull bar (but is an elevated feed type - has a bit of height built in). I like that mounting, because I can see it, and it still works very well there......can't trust myself not to wipe the thing of the roof with a low branch.
AnswerID: 110485

Reply By: Member - Paul P (Bris) - Monday, May 09, 2005 at 17:24

Monday, May 09, 2005 at 17:24
G'day

I run a GPI off my bullbar also. My installer stated that it did not matter were it was, it behaved as if it was mounted in the centre of the roof.

Use a spring base. If there is enough panel gap use a L shapped stainless bracket and an already available panel bolt on the left or right mudguard run using the panel gap between bonnet and guard. Worked on a Land Rover Disco and a 4 runner. Too small a panel gap on my Nissan

Regards

Paul
AnswerID: 110486

Follow Up By: Michael Carey - Monday, May 09, 2005 at 19:31

Monday, May 09, 2005 at 19:31
Your installer is not entirely correct. The radiation pattern from a GI antenna isn't affected by the presence or absence of a ground, BUT metal will affect the radiation pattern. e.g. if you have it mounted on the bullbar, expect it not to work as well behind you as in front. The door pillars, doors, roof, cargo barrier, rear doors, canopy etc. will all affect the signal.
Up high and clear of obstructions is the best place for any antenna, GI or not.
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FollowupID: 367003

Follow Up By: Member - Paul P (Bris) - Monday, May 09, 2005 at 19:36

Monday, May 09, 2005 at 19:36
G'day Michael

Your right of course. The top of mine pokes just a little above the vehicle roof so general allround send/recieve is okay. It does work better to the front though.

Regards

Paul
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FollowupID: 367006

Follow Up By: ColinD - Monday, May 09, 2005 at 20:10

Monday, May 09, 2005 at 20:10
The presence of a large metal surface to the rear (front mount), will cause the signal to lobe to the rear ie. stronger. But because a lot of the signal is obstructed by the roof line, the end result is a weaker signal to the rear. There is no substitute to having the antenna as close as possible in length to the wave length being transmitted, and being located in the middle of an unobstructed ground plane.
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FollowupID: 367014

Reply By: DiesAl - Monday, May 09, 2005 at 18:14

Monday, May 09, 2005 at 18:14
BAz as others have it's ok to mount on the roof or anywhere else for that matter.

Al
AnswerID: 110492

Reply By: Big Bazza - Monday, May 09, 2005 at 20:32

Monday, May 09, 2005 at 20:32
Thanks for all of your replies people. I'm purchasing the AE409L 6/9db antenna, but still a tad confused as to how you attach it to the roof though, what exactly will I need to do to attach it? Hopefully it arrives with instructions...Thanks guys.
AnswerID: 110521

Follow Up By: Sports Junkie - Monday, May 09, 2005 at 21:46

Monday, May 09, 2005 at 21:46
Bazza,

If you bought the "kit", not just the antenna, it will come with a base and cable that will need to be mounted through a hole. I had to ream out the 12mm hole in my bullbar to suit (probably closer to 15 mm). If you intend to mount this in your roof, be prepared to make a large hole in your roof and pull all the lining off to hide the cable. I think you will still end up with an unsightly lump in your roof lining (unless you have a console to hide it). The mounting kit is designed for bullbar mount and only the top thread protrudes above the hole. I would recommend bullbar mounting it if you have one. The 9db assembly is quite long and would make height clearance a real problem in urban areas.
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FollowupID: 367027

Reply By: Groove - Tuesday, May 10, 2005 at 07:55

Tuesday, May 10, 2005 at 07:55
Bulbar mounting is certainly easier but if you would rather it on the roof you can get gutter mounts which clamp to the roof gutter (if your car has them, Patrols 80 series etc). No holes necessary I find the rubber seals on doors wont crush coax cable.

Not as good as dead centre in the roof for radiation pattern but a good compromise.

AnswerID: 110579

Reply By: signman - Tuesday, May 10, 2005 at 10:44

Tuesday, May 10, 2005 at 10:44
G'day Bazza
I have the ground independent set up attached to a bracket on the Rhino Rack bar- drivers side. Around town i have the small 'rubber ducky'type whip about 15cm long. When touring we fit the longer (about 60cm) whip.
From what I understand if you just mount the whip to say the bullbar or roof it gives about a 4.5db gain but sitting on the ground independent tube you get a proper 6.5 db gain ie. better transmit performance.
I do have the assembly spring mounted.
AnswerID: 110592

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