Roof gutter mount or roof center mount for antenna?

Discussion in 'On the Road' started by N7BKV, Dec 26, 2018.

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  1. N7BKV

    N7BKV Ham Member QRZ Page

    Is there much advantage of mounting the UHF antenna centered on the vehicle (Jeep Cherokee) roof over a side bracket or gutter bracket?

    Thinking of going with a Comet CSB-750A antenna.

    Comments appreciated

    Brian N
    N7BKV
     
  2. AF9US

    AF9US XML Subscriber QRZ Page

    Brian:

    The short and simple answer to your question is YES!

    To expound:

    • Gutter Bracket - A clamp that holds the UHF female connector with attached coax, the clamp is designed to grip the gutter rail on the left-side of the roof, or, the gutter rail on the right-side. Disadvantage: unknown electrical connection to the nearby potential ground plane - the roof of the Jeep Cherokee. Additionally, the car is outside in the weather, the unknown electrical connection to the car body is subject to oxidation caused by the weather.
    • Side Bracket - I don't know what the actual mount is. A ball mount, is mounted on the side of the vehicle. A trunk-lip mount could be side-mounted to the tailgate of a vehicle. Any body part that is hinged to the rest of the vehicle does not offer a ground plane as good as a through-the roof mount centered in the middle.
    • Luggage rack mounts - not a good choice when there is a better one only a foot away on the center of the roof. Depending on the vehicle, most luggage racks are mounted to the roof with plastic parts. Thus, electrically isolating the antenna on the luggage rack from the body of the car.
    • Mounting the Comet CSB-750A antenna on a roof mount in the center of the roof of the Jeep Cherokee is the best location for best radiation pattern. This mounting location requires a female UHF connector with attached coax. This mounting location requires the most work.
      • Drilling a hole in the roof of the vehicle, close to the interior dome light (for ease of working with the mount and coaxial cable on the interior of the car). Objectives to meet are 1) Excellent electrical connection to the car roof, and 2) Weather sealing the mount.
      • Routing the coaxial cable from the roof down to the location of the radio inside the car. Being able to work with the ceiling, metal and plastic covers in the interior is a highly desired skill.

    The center of the roof, through the roof mount affords the best signal - transmit and receive, from your mobile. If a marginal signal - especially on the fringe of the repeater is acceptable, that is the coverage you'll end up with by using an antenna mount with an unknown and variable electrical connection to the car body.

    Lastly, depending on the age of the vehicle, you may want to electrically bond the hood, doors, and trunk to the car body. The exhaust pipe may need grounding to the car body if you intend to operate SSB, AM, or on HF.

    Obtaining the assistance of a ham friend who has a good signal from their car, is a good idea.

    Good luck,
    Bernie, AF9US
     
    N7BKV likes this.
  3. KB3WFV

    KB3WFV Ham Member QRZ Page

    A gutter mount will work OK, a magnet mount will work better, a through the roof mount will work the best.

    It has to do with the tx signal return path to the radio. The better the physical connection to more metal (rather less) directly under the antenna. the better the performance of the antenna will be.

    This site has a lot of good information

    https://www.k0bg.com/

    Might want to look at this page

    https://www.k0bg.com/eff.html

    and this page

    https://www.k0bg.com/antmount.html

    and finally this may help

    https://www.k0bg.com/options.html

    Brian
    KB3WFV
     
    N7BKV likes this.
  4. N7BKV

    N7BKV Ham Member QRZ Page

    Thanks AF9US and KB3WFV. That's exactly the info I was looking for. As my next project on the Jeep is to remove/refurbish/reinstall the headliner hard board with new fabric, I will incorporate the cable installation and routing since all the trim and panels will be off.
     

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