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Old 05-27-2018, 2:16 PM
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Default Ground plane on car with sun roof.

I tried installing CB in my wife's car that has a sun roof. Of course the SWR reading was a nightmare. What would it take to keep the antenna on a car's roof that has a sun roof?
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Old 05-27-2018, 2:24 PM
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I never had an issue with my wife’s car and her sunroof, antenna was mounted more towards the center of the roof behind the sunroof.
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Old 05-27-2018, 2:41 PM
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My wife's car is a Hyundai Accent model, so the roof does not encompass a whole lot of metal surrounding the antenna.
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Old 05-27-2018, 2:55 PM
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Quote:
Originally Posted by SnowWalker View Post
My wife's car is a Hyundai Accent model, so the roof does not encompass a whole lot of metal surrounding the antenna.
You are kinda screwed, not enough metal for a ground plane at 27 mHz.

The commercial NMO27 may work on a mag mount. Another idea, NMO27 on a 'hood' mount.
The NMO27 seem to work better in poor or lack of groundplane, the other half of the antenna, applications.
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Old 05-27-2018, 3:39 PM
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This antenna may help:

Laird Technologies C27S

'DC grounded base-loaded antenna. Higher power handling and less ground plane required than standard base loaded antennas. Internal and external contacts are gold plated for best conductivity.'
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Old 05-27-2018, 4:22 PM
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You will never get a perfect ground plane on a passenger vehicle.
Especially on a car that small. Add in a sun roof, and you are stacking the deck against yourself.

But having a good antenna makes a difference. I've put a lot of Larsen NMO-27's on pickups and SUV's and had excellent results, even with less than ideal ground planes. Never had an issue getting them right down to 1.1:1 SWR on the center of the CB band, with about 1.3:1 on channel 1 and 40.
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Old 05-28-2018, 12:14 PM
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The shorter the antenna the worse they are for performance and match.
All antennas that rely on a 1\4 wave GP in all directions will be a compromise in performance.
A base loaded 1\4 wave antenna like a K40 would be best
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Old 05-28-2018, 4:39 PM
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Hyundai calls it a sunroof, yes. But that's a glass panel, which is what Lincoln Mercury trademarked as a MOONROOF and properly that is still called a moonroof. A sunroof would be less of a problem, as the metal is still capacitively coupled to the rest of the roof. With a glass MOONroof, it simply isn't going to be counterpoise.

What you've got, if you try different locations on the metal aft of the moonroof, is that the A, B, and C pillars will be your effective ground radials connected down to the body of the car. Sometimes a difference of a few inches makes a big SWR difference. Sometimes, the antenna setup or the way you're using the SWR meter is an issue. If it is all unacceptable, look for a "no ground plane" antenna for the car.
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