First mobile Jeep (jk) Antenna

Discussion in 'On the Road' started by K2IRE, Aug 18, 2016.

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  1. K2IRE

    K2IRE Ham Member QRZ Page

    Thanks for all the continued feedback!

    I've been logging some decent overtime at work, but from some reading that I've done, it seems 1/2 wave antennas are less reliant on the ground plane. Am I making that up?
     
  2. WA2LXB

    WA2LXB XML Subscriber QRZ Page

    I have to think on that because I'm not intuitively antenna savvy...but my quick answer is that the ground plane in a vehicle mounted vertical provides the reflected half of a vertically polarized dipole...so a 1/4 wave vertical omni on a Jeep hood becomes a 1/2 wave dipole once the reflected image is considered. You may increase gain with a 1/2 wave whip, but the need for a good ground plane remains if you're going to keep an even multiple (image) of the desired wavelength. I believe this is somewhat for resonance, but more for matching the antenna feed point impedance to what the radio wants to see. This gets back to my recommendation to use an antenna analyzer.

    I believe I read that the magnet on a roof mount capacitively couples to the ground plane of the vehicle, but it's not ideal. This is why I understand that it is better to use an antenna designed to through-hole mount to a vehicles ground plane.

    Corrections to the above welcomed by more seasoned and knowledgeable posters.

    http://www.arrl.org/files/file/Ante...al Files/Antennas 101 - 2013 - The Basics.pdf



    http://www.qsl.net/l/lu7did/docs/QRPp/09.pdf

    http://www.arrl.org/forum/topics/view/538

    https://en.wikipedia.org/wiki/Dipole_antenna
     
    Last edited: Aug 22, 2016
  3. KG5JPG

    KG5JPG Ham Member QRZ Page

    while we are on the subject of Jeeps, I drive a 2000 model Wrangler with the Fiberglass top. would it be worthwhile to secure a flat plate of sheet metal to the roof to use a ground plane for my mag mount antenna? I have no issues with drilling a few holes in the roof to mount it. my thought was it would not only work as ground plane but give me somewhere to allow the mag mount to "stick" to. My antenna currently sits on the ARB bumper on the front. I use it for both a Baofeng HT and my Kenwood V71. thanks, PG
     
  4. KD2IAT

    KD2IAT Ham Member QRZ Page

    Parking a sheet of steel on the outside roof of your Jeep is tantamount to planting a rust farm up there. For 2M, it needs to be about 38" in diameter for a proper ground plane. No matter how you paint it, it won't stand up to mag mounts and the elements.

    There are plenty of previous threads about installing a ground plane on the inside of a fiberglass roof. While a metal plate will work, it's easier to use HVAC tape or even metal window screen. In the old days, we used copper window screen material. If you're willing to drill holes for screws for a metal plate, you'd be better served by drilling for the antenna mounts(s) and using thick surface NMO's and have a right proper install. One added benefit is that you won't have your coax crimped in a door or window opening. Sooner or later, coax fails in that situation.
     
  5. WA2LXB

    WA2LXB XML Subscriber QRZ Page

  6. K2IRE

    K2IRE Ham Member QRZ Page

    The more I read the more confused on this particular application I become lol.
     
  7. WA2LXB

    WA2LXB XML Subscriber QRZ Page

    I understand. Here's another thought: I know that you just got your Technician license, but I think you'd really benefit from the General license ARRL study guide. Much of the antenna theory and practical application information that was skin-deep in the Technician study guide is explained in greater breadth and depth. Even if you don't plan to get your General now, get the study guide...even a used one...and flip to the section on antennas.

    Good advice has been given, above. Your confusion is in which plan of action you wish to follow, which is basically: 1) Get a high quality dual band mag mount and put it on your hood; or 2) Install a ground plane underneath your fiberglass top (galvanized hardware cloth works) and drill your antenna into the roof and make sure it contacts your ground plane. In the latter case, use either a very flexible whip or a folding antenna mount to allow your Jeep to get under the bar at the parking garage.

    If you wish to stick the antenna on the spare tire rack, go for it...just realize that your antenna radiation pattern is going to look like a mangled amoeboid...which will make transmitting and receiving less predictable and will alter your antenna feedpoint impedance.

    Mag mount is easiest and will get you on the air soonest...and if you install a better antenna later, you can use it on another vehicle or as a backup.
     
  8. K0UO

    K0UO Ham Member QRZ Page

    Tailgate is not grounded good on JK . I run grounding straps then that'll work pretty well. See the picture of my JK with HF antennas also on qrz web page.
     
  9. N7WR

    N7WR Subscriber QRZ Page

    I helped a friend install a public safety VHF radio in his JK. We used an "L" bracket with hole for NMO mount in the seem between the hood and windshield on the drivers side. He uses a Larson 2/70 dual band antenna and it works fine. When he is in town and doesn't need the gain of the Larson he just used a 1/4 wave antenna.
     
    N0TZU likes this.
  10. KF6UPP

    KF6UPP Ham Member QRZ Page

    For sure don't put it on the side of your Jeep. Going through brush will catch it and tear it off. The best spot is a Mag Antenna on the hood but lots of people think that looks a bit "Lame". The next best is on the back, level with the top of the Tub .
     

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