A different kind of mobile 2m antenna.

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KJ4ZQK, Dec 28, 2010.

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  1. KJ4ZQK

    KJ4ZQK Ham Member QRZ Page

    Does anyone know if anybody makes a 2m mobile antenna with a counterpoise?

    I drive a gas tanker. I am in and out of this truck daily. I can't us a magmount as the roof is aluminum, so I will be using a clip on mirror mount. The problem, no metal under the antenna. The built in coax is appalling so I won't screw into the built in system. Given the poor operation of CB in these trucks I am pretty sure the problem lies in the lack of an RF mirror for the antennas.

    The antenna can be no more than 1/2 wave long or my max legal height will be exceeded. At this point I am waiting to get my Antenna Book and am thinking of trying to build something on my own, though this seems like a waste of time considering the low cost of most mobile 2m antennas out there.

  2. W5RB

    W5RB Guest

    A collinear antenna would work better in the circumstances , but is likely to exceed your height limit . If your mirror mount is metal , it probably will offer a suitable counterpoise , since ~ 19 inches is plenty , compared to the much greater length needed to be effective for CB .

    Dunno if it's a possibility in your installation , but Hustler makes a ground plane skirt , designed to convert its mobile antennas for base use , have a look and see if it's something that could work for you .

  3. W8JI

    W8JI Ham Member QRZ Page

    The mirror, assuming it is reasonable size truck mirror with metal frame, should be an adequate counterpoise for two meters. It would be like having a ten foot mirror frame for CB.

    73 Tom
  4. AC0FP

    AC0FP Ham Member QRZ Page

    Several manufacturers make a "no ground plane" 1/2 wave length antenna for 2 meters, I think MaxRad makes some. These antennas are generally intended for use on fiberglass boats and cars where there is no ground plane available.

    Don't make the mistake of listening to those who will tell you how much better this type of antenna will work if you mount it over a ground plane! :(


    fp :)
  5. K9ASE

    K9ASE Ham Member QRZ Page

    what about mounting to the frame of the tractor behind the cab instead of the mirrior the highth may put the antenna above the cab but not beyond your restriction?
  6. KA9MOT

    KA9MOT Ham Member QRZ Page

    Your max legal height is 13' 6". You should be able to run an antenna at least 5 feet long. I don't think antenna height counts for your max legal height anyway. You just need to be able to clear bridges. Do you need to clear a Boom for loading?

    I used to use my right CB antenna as a "feeler" for low bridges. If the antenna hit (very low speeds) move left or back out.

    On my last truck, I modified the mount of an Arrow Antennas Dual Band J-Pole to work on the right mirror of my 379 Pete. That son of a gun worked good and I still use that antenna today here at the shack.


    Look close, you'll see it on the right mirror (The truck is dirty). You will also see a Larson Dual Band NMO that did not work as well as the Arrow:


    BTW, This truck had 1.6 million miles on it. The paint is faded but she was in excellent Mechanical condition and LOOK! NO DENTS!!!! A big truck with no dents is hard to find now-a-days.
    Last edited: Dec 28, 2010
  7. KA9MOT

    KA9MOT Ham Member QRZ Page

    Yeah because all VHF/UHF antennas work so well when surrounded by steel! NOT!!!!
  8. AD5MB

    AD5MB Ham Member QRZ Page

    decoupling sleeve. solder a 1/4 wavelength conductor - copper pipe, or a shield from a larger cable - to the mounting end of the coax shield. if you disassemble a standard 2.1 dBi wifi antenna you will see that it consists of 1.25" of coax with the shield stripped off, and a 1.25" decoupling sleeve soldered on. that's why they have that characteristic taper halfway up.

    I would verify the SWR and resonant frequency with an MFJ-269 before I trusted my finals to it.
  9. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    How about putting a magmount out on the hood! (if you aren't driving a cab-over).
  10. KF5GCL

    KF5GCL Ham Member QRZ Page

    I have wondered about that. Are you suggesting that it won't work better than a conventional antenna, or that it won't work at all? What's the story on that?
  11. KA9MOT

    KA9MOT Ham Member QRZ Page

    Most truck bodies are made or Aluminum and/or Plastic. The hoods are usually plastic.
  12. AC0FP

    AC0FP Ham Member QRZ Page

    It works as advertised which is as a dipole, it has some gain over a 1/4 ground plane. If you were to place the 1/2 wave 2 meter antenna over a ground plane it would become a 1/4 wave ground plane antenna at 4 meters!


    fp :)
  13. K8ERV

    K8ERV Ham Member QRZ Page

    1.6 million? Time for an oil change.

    TOM K8ERV Montrose Colo
  14. K9ASE

    K9ASE Ham Member QRZ Page

    seems to me most tankers don't have sleepers and the trailer is not as close to the cab as a 53' Box. depending on where the 5th wheel is set. But no one was talking to you!
    Last edited: Dec 29, 2010
  15. KA9MOT

    KA9MOT Ham Member QRZ Page

    IT's a PUBLIC FORUM.....You are talking to everybody.

    Go buy an Antenna Book. You have allot to learn. Your reason for editing is listed as, "Wrong Idiot". Go look in a mirror. You haven't been a Ham for even a year yet, and with your medical condition you've never driven a big truck. You have little knowledge of either subject.

    While it is true, his tractor (That is the part in the front) may not have a sleeper, and there may be 300 inches (an exaggeration) between the rear of the tractor (the front part) and the trailer (That is the long part in the back) the VHF/UHF antenna is still going to be surrounded by metal plus it would only be 4 feet off the ground.

    Since you are qualified to call people idiots, try to explain to me (The right idiot) how that is going to work.

    I apologize if I hurt your feelings when I scoffed your advice...bad advice is bad advice and you should at least make an effort to understand the subject before you give advice....Don't get mad, when somebody points out that you are mistaken.
  16. K4EEZ

    K4EEZ Ham Member QRZ Page

    some thoughts...
    can you not find a mount for the door like a lip mount?
    and mount it to the top of the door frame

    I did this once to a lip mount and bent the mount so it was at a 10 deg pitch, it worked fine as there are 2 Alan set screws
    that binded to the metal door frame for good ground connection i then thattached it to the passengers side door and also
    installed some of the weather insulation fome... worked really good.

    also if you ran a ground wire from the radio chassie to ground somewhere in the cab the radio would then be grounded.

    Another idea would be to find one of them Large rear earth magnets and then put the mag mount on the center of the Alu. roof
    and locate the mag mount via the rear earth magnet, your need to find the North and south poles so they attracted and not
    propel each other, being so strong in flux the mag mount wont move. look at the hussler 5/8th wave antenna i think its 54
    inch whip and none taped to ground I use one of them my self, but not only for 2 meters use, it can be used on 6 meters
    as well as it is pretty close to a 1/4 wave electrical length for 6 meters.

    hope this helps 73 good luck.
  17. VA3CQC

    VA3CQC Ham Member QRZ Page

    I have one actually! Maxrad MDA-1501, it's an all aluminum vertical dipole. It has a little arm which clamps onto whatever you like. Mine is mounted on a brick chimney and needs no ground plane.

    If you mounted this on your mirror arm, someone reaching out from the window could grab it... not the best situation but I bet the performance would be amazing.
  18. KB0YYO

    KB0YYO Subscriber QRZ Page

    I knew a driver in KY the pulled gas tank. He mounted his antenna in the middle on top of the trailer near the cupola. He put it on the grab rail .It seemed to work for him.

    I use a Diamond quad band on my right mirror .Freightliner.Century. . works very well for me.

    Last edited: Dec 29, 2010
  19. W8JI

    W8JI Ham Member QRZ Page

    ANY vertical antenna always works better, to some extent, when mounted over an adequate groundplane. Sometimes the difference is large, sometimes unimportant, but there is always a difference. Even a half wave antenna requires a ground of some type to push current up into the antenna.

    Also, a sleeve over the coax will NOT take coaxial line shield currents to zero. The is because the sleeve to coax impedance at the open end is not infinite. People mostly kid themselves when they fold a braid back over the cable and pretend it is an effective isolation device.

    I expect the mirror is a better ground than you think.

    73 Tom
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