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Author Topic: Magnetic antennas near roof rack  (Read 1306 times)
W1EPF
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Posts: 7




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« on: November 06, 2002, 06:54:51 PM »

Hi folks,

I have a Jeep Liberty with a Kenwood TM-G707 dual band.  I have a Diamond 7500 magnetic mount antenna on the center of the roof.  Last weekend I had to put the cross bars on for the roof rack (metal tubing with vinyl covering).  The antenna is about 3 inches from the cross bar.  Combined with the snow we've had here in New England recently, it seems that I'm picking up a lot of static that breaks squelch.  Also, I was not able to reach a repeater that I can ususally get without any problem.

My question is...am I getting some extra coupling because of the roof rack, is it the snow, or just plain old bad luck.

Thanks for the help
Ed
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K0BG
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« Reply #1 on: November 06, 2002, 07:19:33 PM »

Probably a little of both.

Personally, I do not like mag mounts for a variety of reasons. If it were mine, I'd find a place in front of the rack, and permanently mount a loaded 5/8 wave Larson, or similar good-quality antenna. While difficult, it is possible to route RG58 thru almost any headliner. If you have a low clearance into your garage, then install a spring on the top of the loading coil. If the loading coil won't clear, then even a 1/4 wave permanently mounted antenna will usually out perform a mag mounted 5/8 unit.

Alan, KØBG
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WB2WIK
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Posts: 21836




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« Reply #2 on: November 07, 2002, 11:33:31 AM »

I'll ditto the vote for "hole mount" antennas, over mag mounts.  

Not only do they work better, but they are far less likely to scratch the car's finish, attract attention, and be stolen.  Slamming a car door on coax doesn't do it much good, either -- that's a failure in process starting the first time you do it.

But even a "through hole mount" whip will still be affected by snow and ice building up around it, so definitely clean that off if you expect good performance from the whip.

As for routing the coax from the roof mount (hole mount) antenna to the rig, I have a perfect solution for that, one that I've used on many cars over the past 20+ years:

I get the local body shop to do it for me.  Actually, the headliner in any car or truck is easy to remove, and I do that part myself.  Then I punch the hole for the antenna mount, install the mount, and route the coax in the approximate direction I want it headed, using duct tape or something to temporarily hold it against the roof underside.

Then, I drive to the local body shop, who has the tools and experience to re-install the headliner perfectly and quickly.  In my last vehicle, it was even easier because I live only 3 miles from an "auto upholstery" shop that repairs auto interiors, and one of their normal services is to replace headliners that have become soiled or torn.  So, they are REALLY good at it.

They took seven minutes (I clocked it) to replace my headliner, perfectly, exactly as the factory had originally done it.  I tried to pay the guy $20 for his efforts, but he wouldn't take it.  So, I went to the donut shop and bought two dozen donuts for everybody in the shop, and they were very happy with that!

WB2WIK/6
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WA9UAA
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Posts: 360




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« Reply #3 on: August 16, 2003, 10:45:00 PM »

Hi Ed,
Water under a mag mount will change the coupling between it and the roof of the car thus detuning your antenna system. If you have some snow melt thats probably one of the causes. The other posts are right about the mag mount. I am not that familiar with the roof rack on the Liberty, a clamp on mount might be a possibility. HTH
73,
Rob
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