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Sunroof's effect on ground plane of the roof

Discussion in 'CB Radio Forum' started by sundown556, Apr 4, 2011.

  1. Apr 4, 2011 #1
    sundown556

    sundown556 Bobtail Member

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    Apr 2, 2011
    Phoenix, AZ
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    I've got an SUV with a sunroof and was wondering what effect, if any, the "gap" in the roof metal has on a CB radio antenna's ground plane and associated radiation "cloud". I'm open to suggestions, but was planning on installing an antenna behind the sunroof to get as close to center in the roofline as possible.

    Would the sunroof's gap plus the gap of the windshield between the hood and extreme front metal part of the roof cause a radiating gap? Not sure how that sounds when you read it, but I can't figure out a better way to describe it.

    FYI, the sunroof also has a sliding panel beneath the glass of the sunroof and the sliding panel has a reflective surface, kinda like those reflective screens you put up on your windshield to keep the sun from REALLY heating up your cabins. It's not metal, more like a metal film glued to a flexible backing.
     
    sundown556, Apr 4, 2011
    sundown556, Apr 4, 2011
    #1
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  3. Apr 4, 2011 #2
    jessejamesdallas

    jessejamesdallas Road Train Member

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    No effect what so ever...Nothing to worry about there...Although I would suggest having your antenna mounted closer to the rear of the roof instead of the middle...On SUV's with long roof lines like Suburbans, the antenna's seam to tune better towards the back vs. the center...
     
    jessejamesdallas, Apr 4, 2011
    jessejamesdallas, Apr 4, 2011
    #2
  4. Apr 4, 2011 #3
    handlebar

    handlebar Heavy Load Member

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    The gap left by the sunroof, open or closed, will affect the total capacitance that your antenna looks for the car's body to supply to reduce ground losses. However, there's nothing practical to do about it. Given your situation, I'd try to mount the antenna as near the center of the piece of roof that's behind the sunroof hole, equidistant between the rearmost edge of the roof hole and the top of the rear glass. That will help take advantage of the available symmetry.
    -- Handlebar --
     
    handlebar, Apr 4, 2011
    handlebar, Apr 4, 2011
    #3
  5. Apr 5, 2011 #4
    xPosTech

    xPosTech Light Load Member

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    The center point of the roof that's behind the sunroof would also seem to be far enough back to not interfere with the retraction of the sunshield and sunroof. You don't want to hard mount the antenna and then find out you can't fully retract the sunroof.

    Also when routing the cable take care to not interfere with the sunroof drain line(s).

    Ted
     
    xPosTech, Apr 5, 2011
    xPosTech, Apr 5, 2011
    #4
  7. Apr 5, 2011 #5
    Turbo-T

    Turbo-T Road Train Member

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    I've ran a mag mount on a sun roof SUV right behind the sun roof no problems.
     
    Turbo-T, Apr 5, 2011
    Turbo-T, Apr 5, 2011
    #5
  8. Apr 5, 2011 #6
    jessejamesdallas

    jessejamesdallas Road Train Member

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    And if you check your SWR witth the sunroof open, or closed you will notice no difference on your meter too...

    Unless your sunroof retracts like a convertible-top, that small hole created by having it open, is not going to do squat in regards to SWR...Unless they have developed some new kind of sunroof in the last 40 years I'm unaware of...
     
    jessejamesdallas, Apr 5, 2011
    jessejamesdallas, Apr 5, 2011
    #6
  9. Apr 5, 2011 #7
    delta5

    delta5 Road Train Member

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    The only way to really find out is with the use of a field strength meter...
     
    delta5, Apr 5, 2011
    delta5, Apr 5, 2011
    #7
  10. Apr 13, 2011 #8
    sundown556

    sundown556 Bobtail Member

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    Well, due to the sunroof glass retracting back underneath the metal roof portion behind it, the CB shop installed it pretty much close to the back of the roof, right behind the last left-right rung of the roof rack. It's a Wilson 5000 permanently mounted but when you remove the coil/whip and put the weather cap on it, you can hardly see it. Radio is a Cobra 75 for removable setup with little visual clutter.

    Antenna tuned to 1.1 and range to the rear (with that tiny remaining portion of the roof as groundplane) was about 4 miles; I checked in with the CB shop as I drove off. So I imagine forward range would easily equal that. So all in all, an effective setup. Hope this helps someone in the future.
     
    sundown556, Apr 13, 2011
    sundown556, Apr 13, 2011
    #8
  11. Apr 14, 2011 #9
    jessejamesdallas

    jessejamesdallas Road Train Member

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    Told ya! No bigger a hole than what a Sunroof has, just not going to be a factor...As for ground plane effect from the hole, you still have metal under the open hole! It's called the "Floorboard"....
     
    jessejamesdallas, Apr 14, 2011
    jessejamesdallas, Apr 14, 2011
    #9
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