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Capacitance Coupling via Magnetic Antenna Mount

Discussion in 'CB Radio Forum' started by BTShepp, Feb 3, 2017.

  1. Feb 3, 2017 #1
    BTShepp

    BTShepp Blue Demon

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    Oct 31, 2015
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    A lot of operators--CB and ham alike-- have mixed, if not negative, opinions towards the quality of ground that a magnetic mobile antenna allows for. It's understood mathematically that the higher the frequency, the more efficient the coupling is, making the antenna a great, or at least decent, choice for VHF and UHF applications. Larger bases provide more surface area for a better capacitance coupling to the vehicle in addition to a stronger physical bond to the vehicle, keeping the whip in place.
    But down here in the 11 meter band, is the capacitance coupling enough to make the magnetic antenna reasonably efficient, for lack of a better term? Is it inferior, superior, or comparable to a "hard" ground, all else equal?

    Below is an interesting article in support of magnetic antenna systems; indeed, it is one of the few in support of magnet antennas.
    http://www.cosjwt.com/index.php?a=3
     
    BTShepp, Feb 3, 2017
    BTShepp, Feb 3, 2017
    #1
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  3. Feb 4, 2017 #2
    Ridgeline

    Ridgeline Road Train Member

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    I brought up the question and no one seemed to get it.

    With a magnetic mount antenna, a lot of issues go away, why do they work better than some of the mounted setups on vehicles?
     
    Ridgeline, Feb 4, 2017
    Ridgeline, Feb 4, 2017
    #2
    BTShepp Thanks this.
  4. Feb 4, 2017 #3
    Meteorgray

    Meteorgray Heavy Load Member

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    The only antennas I use have magnetic bases, from the 3-foot K30 on the trunk of my Mazda to the 5-foot Wilson 1000 on the roof of my F250.

    I like the magnetic design because of the enormous versatility of being able to place the antenna where it is the most advantageous and being able to remove it when not needed.

    On my car, I get the best SWRs with the antenna on the center of the roof, but I can't drive it into my garage with it there, so it goes on the lid of the trunk, where it fits into the garage just fine. The compromise is that my SWR is at 1.1 on the roof and at 1.5 on the trunk. Big deal. Plus, I often remove the antenna and put it in the trunk because it's not needed until I'm on the open road anyway.

    For my needs, the magnetic mount works very well. I get good SWRs and a range that is quite satisfactory.
     
    Meteorgray, Feb 4, 2017
    Meteorgray, Feb 4, 2017
    #3
    BTShepp Thanks this.
  5. Feb 4, 2017 #4
    BTShepp

    BTShepp Blue Demon

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    Chicago, IL
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    Good point. It's hard to get a fair comparison all of the time, though. Most magnet mounts are placed on metal car roofs with all perpendicular and no parallel metal relative to the antenna. Many hard installs are done poorly-- short antennas, bad placement on vehicle, little to no ground, etc.
     
    BTShepp, Feb 4, 2017
    BTShepp, Feb 4, 2017
    #4
  7. Feb 4, 2017 #5
    BTShepp

    BTShepp Blue Demon

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    Chicago, IL
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    I used to think magnetic antennas were inferior and marketed for their convenience over functionality. I'm learning that they really give hard installs a run for their money, possibly exceeding many "permanent" mobile set ups.
     
    BTShepp, Feb 4, 2017
    BTShepp, Feb 4, 2017
    #5
  8. Feb 4, 2017 #6
    rabbiporkchop

    rabbiporkchop Road Train Member

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    Magnet mount on roof could outperform 9 foot whip on trunk lid.
     
    rabbiporkchop, Feb 4, 2017
    rabbiporkchop, Feb 4, 2017
    #6
    BTShepp Thanks this.
  9. Feb 5, 2017 #7
    BTShepp

    BTShepp Blue Demon

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    BTShepp, Feb 5, 2017
    BTShepp, Feb 5, 2017
    #7
    DRAGON64 Thanks this.
  10. Feb 8, 2017 #8
    craig_sez

    craig_sez Road Train Member

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    Ill offer my 2 canadian cents worth when my sirio mag ant gets picked up in a week and a bit..
    Ill have a stryker hpc2 and sirio mag mount on my hemi hopefully by then..
    Mark is shippin it out fri..
    Dont know how i keep finding myself in this darn loop....
    I had about 6 different radios and got down to two..Now in back to 6 again..
    My 1st cobra 29 from late 90's
    A cobra chrome with midnight 250 linear
    My 1st stryker 955
    My 2nd stryker 955
    And my newest stryker 447hpc2..
    Gonna have to sell the chrome,midnight 250 and a tx star high drive 350...
     
    craig_sez, Feb 8, 2017
    craig_sez, Feb 8, 2017
    #8
  11. Sep 18, 2017 #9
    CETjourneyman

    CETjourneyman Bobtail Member

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    Sep 18, 2017
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    Very simple. Because with a mag mount at 11 meters, your looking at a 5 ft whip and the other 4ft is coiled up as an inductor between the whip and magnet. The inductor equalizes the impeadance to 50 ohms with or without a proper ground plane thus giving low reflected power. A standard 9ft 1/4 wave whip (no inductor) must have a matching full size ground plane to acheive 50 ohms. any less than that and you run into an impeadance mismatch/reflected power. Same with 5/8 wave fiberglass antennas but the inductor is top loaded.
     
    CETjourneyman, Sep 18, 2017
    CETjourneyman, Sep 18, 2017
    #9
    lilillill Thanks this.
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