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GMRS antenna mount location

lwimi48

Newbie
Joined
Aug 26, 2020
Messages
2
Hello:
I am currently looking at mounting a 6 db (30 inch) GMRS antenna to the top of our motorhome, right in the roof since it would serve as the perfect ground plane. I basically have two spots that will work for where I can drill the hole and run the cable. The best spot, would be about 18 inches away from the AC unit (which is about 13 inches high, or in other words, sticks up about 13 inches above the ground plane next to the antenna). Would there be any concern with the AC unit being too close (could it interfere or block the signal being this close?).

There's another spot more open, but it would be only about a 13 inches away from a 30 inch FM antenna that has a spring base on it, so I am trying to avoid this spot to keep the antennas from touching each other while on the road.

I really appreciate the feedback. Hopefully this is a simple answer.
Chris
 

KOK5CY

Member
Joined
Jan 6, 2005
Messages
386
Location
Afton, Ok
If your roof is metal it'll work but keep it away from your a.c. unit . but if it's fiberglass it's a no go . you'll need a spot that's solid metal for a decent ground plain .
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
13,829
Location
SNCZCA01DS0
First, be sure your roof is actually metal. Not all of them are. Some are steel/aluminum framing with plywood and a membrane over the top.

If it's not a metal roof, then you may want to consider using a 1/2 wave antenna.

I'd stay away from the FM broadcast antenna if you can. Likely won't hurt the radio, but it will desense the FM receiver when you transmit. 13" away from the A/C unit likely won't be an issue, but you do want the antenna in the clear if you can.
Also, beware of low clearance. My trailer is 12' 6" at it's highest point, which does become an issue on some forest roads. Make sure whatever antenna you choose, it has a spring in the base.
 

lwimi48

Newbie
Joined
Aug 26, 2020
Messages
2
Thank you very much for the replies. Our motorhome actually has an aluminum roof and the roof height is about 8'10". I was able to move to about 19" away from the AC unit and installed the antenna today (this is about 40 inches from the FM antenna, so hopefully like you said it will not interfere when transmitting). So far so good in testing. Sounds like the AC unit should not cause an issue but if it does my thought will be to relocate the antenna maybe on top of the AC unit and install one of the NMO ground planes but that's a last resort. Thanks again!
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
13,829
Location
SNCZCA01DS0
Thank you very much for the replies. Our motorhome actually has an aluminum roof and the roof height is about 8'10". I was able to move to about 19" away from the AC unit and installed the antenna today (this is about 40 inches from the FM antenna, so hopefully like you said it will not interfere when transmitting). So far so good in testing. Sounds like the AC unit should not cause an issue but if it does my thought will be to relocate the antenna maybe on top of the AC unit and install one of the NMO ground planes but that's a last resort. Thanks again!
Glad it worked.

The A/C unit shouldn't be an issue. My concern was that if you have metal too close to an antenna, you can detune it as well as create RF shadows. 19" away should not be an issue.

If you have the antenna mounted to the roof with a permanent NMO mount, then you'll have an excellent ground plane and it should work quite well.
 
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