View Full Version : ground plane question. Non-issue?

08-04-2009, 04:34 PM
I got tired of holding the HT out the window of the truck last weekend. The least I can do is mount an antenna on the outside of the 4Runner.

I figure I can either:
Drill a hole in the roof of the cab for the nmo mount. (headliner might cause some effort, but the NMO mount will be as low profile as I can get things.

Put an L bracket right behind the cab with the nmo mount on that. Routing the feed line would be easy though the seal between the hard/soft tops into the cab area.

Notes: My cab is 2 door pickup sized with a big sunroof in the middle leaving about 6 inches of metal halo around the top. (not much metal)

Will I be giving up much ground plane by elevating the antenna mount above the metal roof or bed with the L bracket mount?

My guess is no. The electrical ground plane established by the entire truck will affect the radiation pattern of the antenna and mounting the antenna 1 inch higher and 3 inches farther back isn't going to make much difference on my non-optimal mobile mounting.


08-04-2009, 05:00 PM
We mounted the 2 meter antenna on a bracket on the spare tire carrier of the Bronco. I would guess that with the fiberglass top, the Bronco is close enough the the same situation you have with the 4runner regarding ground plane. In our experience, even with low power (5 watts) we were plenty strong in transmit and receive capability. Our situation is probably even worse than your's will be as it was on the back corner of the truck.

The only issue we had was a narrow trail combined with the wide truck, some slippery mud and an aspen tree. I wasn't there but TheBoomBoom swears the tree was very unyielding about making room for the sliding truck and insistent about knocking the bracket off. :eek:

08-04-2009, 05:14 PM
Another thing I noticed is that side mounted antennae spend a lot of time in the bushes on a tight trail like Jenny Creek. Those with center mounted antennae rarely hit branches. I see that as an advantage to a center mounted antenna.

My only concern is getting the truck into the garage. A fold over MIGHT do the trick, but I only have about 1 inch of clearance above my 'Runner. I think I'm stuck with removing the antenna each time I pull into the garage. My CB antenna is on a quick disconnect on the spare tire carrier and I never remember to take down the arial when I pull in until I hear the bad noises of straining fiberglass.

I guess the L bracket will cause less damage when I drive my antenna into the garage door frame!

08-04-2009, 05:34 PM
Does the sunroof happen to have a metalized coating? No matter, I would just drill the hole personally. The height alone will make this the best option. You don't necessarily need a huge plane under the antenna, typically even a 1/4 wavelength will be enough to get most of the benefit. For a 2m antenna that's about 19 inches and for 70cm it's only 7 inches. Beyond about 1/2 a wavelength there isn't much added performance, either. Certainly the NMO won't be any worse than a corner bracket and those work pretty decent.

08-04-2009, 05:52 PM
I opted for the mag-mount. Makes it really easy to remove to get into the garage and also easy to swap between rigs. and no drilling required. :)

08-04-2009, 05:56 PM
I have a mag mount that we use for Allison's Jetta. works great.

08-04-2009, 09:53 PM
Those with center mounted antennae rarely hit branches. I see that as an advantage to a center mounted antenna.

That's funny cause TheBoomBoom managed to come back from his trip to Red Cone without the center mounted antenna that replaced the one the aspen tree ate a few weeks ago. :hill:

08-04-2009, 11:36 PM
Hmm, OK Ricardo, so no where is safe for the antenna on a bronco! Funny, I never lost one on my 1980 Bronc'.

Metalized sunroof? I doubt it. It is blue. I have an amber one as a spare too. I could test 'em and tell you guys which sunroof works better for ham.

I actually like the mag mount idea because it'll tip over, fall off, and scratch the side of my truck (some more) instead of breaking off an/or bending the roof when I drive into the garage.

See y'all tomorrow!