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I just installed a spare-tire mount and Browning BR-180 dual band antenna on my Jeep JK. Initial SWR testing show nothing higher than 1.4:1 across both bands so I didn't try to tweak it.

Then I put the spare tire back on and the SWR shot way up, over 5:1 and worse in some cases. Removing the spare again confirmed the problem, as the SWR dropped back down.

What can I do to resolve this? I know others with similar installations that work fine. I'm not sure exactly what's happening.

These pics are of my installation.

Back view of antenna on vehicle

Side view of mount between tire and rear hatch

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The metal wheel is detuning the antenna.

You'll either need to:

  1. Put the spare inside the vehicle
  2. Move the antenna

I would move the antenna.

And the higher the antenna the better! How about on top of that gray cap? If that truck bed cap is nonmetallic, you'll need a counterpoise to maximize your communications range. That could be made with some metallic tape radials on the inside, properly sized and connected to the antenna's ground (the coax shield through the connector).

EDIT: I just noticed what seems to be a metal luggage rack or roll bar. Can you mount it to that? A better photo of that would help.

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  • $\begingroup$ The cap is removable, so not really an option. The luggage rack is too. I have a feeling moving it up to be even with the brake light might be my best choice. If there are no better suggestions soon, I'll accept this as the answer. Thank you. $\endgroup$ – Lance Mar 2 '17 at 0:12
  • $\begingroup$ @Lance It sounds like you regularly remove both the cap and the rack. When the rack is installed, wouldn't mounting it near the brake light put the antenna in close proximity and parallel to the rack? That would likely detune the antenna also. $\endgroup$ – Mike Waters Mar 2 '17 at 0:50
  • $\begingroup$ It's perpendicular to the rack. The vertical supports are still there, but they are there now too. And without the tire the SWR is fine. I don't think just being a little higher will change how it interacts with the rack. $\endgroup$ – Lance Mar 2 '17 at 4:13
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The metal wheel and the steel-belted tire are big chunks of metal. Those add capacitance between the antenna and ground, so they lower the resonant frequency of the antenna.

A shorter whip or a variable-length whip might work. Some mobile antennas have an adjustable length portion at the tip. If the top of the coil is the common 3/8" thread, you can find a telescoping whip to get the length right, then cut a solid whip to the right length.

Some mobile antennas have a mast section below the coil. These are usually for bumper mounts, but might help here. Search for "Hustler mast".

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I resolved the SWR issue by using an Arizona Rocky Road Mount mount, which raised the antenna above the spare tire. This resulted in SWRs no greater than 1.5:1 across both bands.

Arizona Rocky Road Jeep J/K Mount

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