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Mobile antenna position
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by KC9EOS on June 7, 2004
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I'm getting ready to have a mobile antenna permantently installed, after using a mag mount for some time. The choices for positioning seem to be three: 1) center of roof 2)center of trunk and 3) lip of trunk (off the one side)
I've been told that roof center is optimal, but my installer warns me that leaking could be a problem. He'll do it if I want, but he did warn me not to.
If I had to choose between the two remaining trunk positions, which one is best? The center trunk would still involve drilling a hole, but potential leaking there would not be disastrous.
I'm interested in your thoughts about pattern and gain, and also any concerns about RF exposure in the three positions? Thanks!
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RE: Mobile antenna position
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by WB2WIK on June 7, 2004
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A professional (?) installer warned you about a roof leak? First time I've ever heard of that.
I've owned 19 cars since 1968, and have punched a hole in the center of the roof of every single one of them, and surely never had any sort of leak. The antenna mounts, when properly installed, are extremely watertight (gasketed) and will withstand buckets of water dumped directly on them (as in a car wash!) thousands of times without a single drop of water leaking into the car. That's silly.
Locally our police cars have about sixteen whips mounted through holes in their roofs (hundreds of vehicles) and none of them leak, either.
I suggest you do it yourself, or get another installer!
The center of the roof is by far and away the best location for a whip antenna, and center of the trunk isn't as good -- period. On two meters, I use just a little 1/4-wave (19") whip mounted (permanently, Larsen NMO mount) in the center of my roof and when we do "FM shootouts" locally, I blow away anybody using any sort of trunk-mounted antenna, even if theirs are larger, gain arrays like 5/8-wave, stacked 5/8-wave and 7/8-wave antennas (that end up being far taller than my roof mounted whip). No comparison.
Another "problem" (although it may not exist for your particular car) is that when mounting a whip in the center of the trunk lid, there's a chance that the whip will slam into your rear window every time you open the trunk! (Depends on the car.)
WB2WIK/6
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RE: Mobile antenna position
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by K5LXP on June 7, 2004
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Dittos to WB2WIK's comments, I've had six antennas in the roof of my pickup for a decade now, no issues with leaks. If your installer warns you of this, perhaps *his* installs leak. They don't leak if you do it right.
Mark K5LXP
Albuquerque, NM
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RE: Mobile antenna position
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by KZ1X on June 7, 2004
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My car-roof antenna installs, which are approaching three figures, never leak.
My current vehicle has a power sunroof which precluded a roof mount; even all the way back near the rear windown.
Darned thing.
But I got the car at 6:41 PM on 12/31/02, nearly 2 hours after the dealer closed on New Year's Eve. Talk about a deal ...
... so, my current antenna is mounted in a hole in the middle of the trunk. And it doesn't leak, either.
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RE: Mobile antenna position
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by WTF52 on June 7, 2004
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Truth is, where you mount it won't make a lot of difference to your signal. Of course, the center of the roof is optimal, but who wants to ruin a perfectly good roof on a perfectly good car bring drilling a hole in it. I have mine on the rear driver's side with a diamond K-400 mount. Works great on all bands from 40M to 70CM.
Beware the purists!
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RE: Mobile antenna position
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by AA4PB on June 7, 2004
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I've never had a roof leak from mounting an antenna. I even take antenna off, screw on the NMO cover, and take it thru the car wash from time to time. If your installer has problems with them leaking, I'd probably find another installer.
Punching a hole in the roof is not that big of a deal if you have the right tools. I use drill and a chassis punch of the appropriate size. If you are paying the "going rate", you can probably buy the tools for what the installer costs and you wind up with some tools :-)
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RE: Mobile antenna position
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by KB9ERU on June 7, 2004
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I've been installing NMO mounts professionally for a few years now, and never had a single one leak!
Like the others, I tend to agree. Do it yourself, or get someone else to do the install. I'd steer clear of "Mr. Professional".
I currently run 2 antennas on my vehicle. I have a wideband gain center loaded on the roof, and a VHF gain on the roof. Because the VHF is taller than the UHF, I put in on the trunk lid. It looks really nice that way.
Now I need some more antennas, or a bigger vehicle :)
Mick KB9ERU
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RE: Mobile antenna position
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by N6AJR on June 7, 2004
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I use a trunk lip mount, either the Diamond K-400 for the larger antennas, or the good old hustler trunk lip mount for the smaller ones.
It allows a quick instalation, doesn't look bad, is far away enough not to cook my brain, and it works. I alwasy run a ground Braid from the mount to the chassis of the car .
I can use an extension kit and mount the rig in the trunk and I often run an amp there as well. its easy, and no leaks, and no hole in the roof. on my truck I dill holes in the bed rails for antennas.
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RE: Mobile antenna position
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by KC9EOS on June 7, 2004
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Thanks for all these replies! I appreciate them! Sounds like the leak issue should not be a problem.
Could a few of you address the RF safety factor? I have an Icom V8000 which has a max output of 75w. If running at full power, could the antenna position be a safety factor?
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