How to keep CB magnet mount from scratchin paint?

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  1. 74DartSwinger360

    74DartSwinger360 The Brat Pack

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    What are some opinions on the Wilson 1000 trunk mount?
     
  2. coffeedart67

    coffeedart67 Well-Known Member

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    Have seen a lot of street rodders and corvette owners that just have a small tab coming out from under their rear bumpers and mount a fiberglass whip, then just a wrench and can remove it at a show. I have a Maxon hand held that would probably be more than adequate for caravaning, it did have a docking station that had a handheld mike and external antanea hook up but it is long since gone.
     
  3. 74DartSwinger360

    74DartSwinger360 The Brat Pack

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    We dont really want to buy handhelds because we all have CBs ready to go in our cars.
     
  4. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    That, in effect, was what I was suggesting. If you were to get a little "trick" with this, you could make a "mini receiver" quick disconnect type of thing.
     
  5. yeswedeliver

    yeswedeliver New Member

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    I know this is an older post - but I have the same problem. However, knowing a little about ground plane and Antenna theory - it SEEMS to me [I am not an expert] that the metal to metal contact is important (!). That said, I understand the car paint is not metal - but it still seems an additional layer of cloth, cardboard, plastic ... will inhibit the efficiency. I have used aluminum foil - but was not happy as it weathered and marred that paint anyway. I'd like to hear from an old HAM on the effect of a non conductive material between the magnet and the car... maybe someone has actually measured the difference [in fact, I will post this to an Amateur Radio forum and return if I get some feedback]. Thanks!
     
  6. yeswedeliver

    yeswedeliver New Member

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  7. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    That article is primarily aimed at VHF and above-------they mentioned 50mhz which is the amateur 6M band. That is nearly twice the frequency of CB. "Here's the thing..............." as frequency goes down capacitive reactance goes up........which is the what -you- might-call "conductivity" between the mount and the car. Add to that "if" you add plastic/ rubber/ cork/ other between the mount, which drives the Xc up even more, the "short answer" is the SWR and preformance will suffer.

    Way to revive and old thread LOL

    Also keep in mind the SAFETY of mag mounts. "If they let go" due to reduced magnetic holding power, they can damage your or other's vehicles, as well as becoming a projectile that can hurt living things
     
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    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      Further explanation, attempting to keep this in some context that you can visualize.........The mag mount must 'ground' to the car body, for lack of other.........by capacitance. Capacitance is effected, at least in some ways, by the thickness and type of insulation (dielectric) between the two plates of the capacitor---one being the car body, the other being the metal on the bottom of the mag mount, by the distance such as other objects such as plastic film in between, by the diameter (surface area) of the plates (the mag mount)

      This works like a coupling capacitor, which are used to couple AC signals. An example might be an audio amplifier. Modern microphones often are powered by DC power sometimes called "phantom" power, because that power is sent down the mic cable itself. BUT INSIDE the amplifier, going to the input stages of the pre-amp, this DC power must be BLOCKED from the amplifier circuit, so a COUPLING or DC BLOCKING cap is used. The value (size, capacitance) must be tailored for the audio frequency range. This coupling cap, then, "feeds" the audio AC signal from the mic cable to the input stages of the amp

      What we are dealing with here is RF. Just like the coupling cap above, the capacity of the mag mount is much MORE effective at RF coupling at VHF, and better yet at UHF, than it is at lower, HF frequencies. This coupling, called "capacitive reactance", or Xc, is the AC equivalent, so to speak, of RESISTANCE value of a resistor. This reactance varies with many things in a circuit, as well as the frequency of the AC signal, in the case of CB, of course, about 27mhz
       
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      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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        Another annoying story from the old days (standby)

        SCAN08csd.JPG

        This is the old, unloved, "Skud missile," a low flying, poorly guided object. 1978 Ford LTDII, 351W 2bbl. The photo was a "last thought' as I turned it over to the junk yard. I bought it when I was broke in the '80's for 300 bucks with a broken cam gear and bad crank. Got it running, and drove it to work for 3 years or so. I had a Tempo (Uniden) 2020 transceiver which I used on the amateur bands, installed in the car. HUGE radio. MADE MY OWN mobile whip for 10 through 160meters. The system consisted of a pipe nipple welded to a home-built hitch receiver, with 1/2 pipe PVC coupling screwed on for a base insulator, and about 4? ft of scrap 1/2 pipe into that, with a diagonal brace about 1' high to keep it "in place." At the top of the 4' pipe, I screwed various PVC fittings on, with HAND WOUND loading coils for the various amateur bands, and topped it all off with a broken off CB whip about 6' or so ft long. The whole damn thing was over 12' to the top, and HIT SOME LOW overpasses!!!!! By removing the loading coil, and coupling the top whip directly to the 1/2 pipe it was "just right" for the amateur 10M band

        The infamous (and huge!) Tempo 2020

        a_tempo2020.jpg

        I was working in Spokane, about 50mi drive one way, and had several "adventures" in that car. One afternoon, coming home from work, had the "cruise" turned on, and "not much" happening on the amateur bands. I was on either 15 or 20M trying to get my morse code speed "up" and had one hand on the wheel, the other hand, my arm resting on the console, tuning the radio, trying to "copy in my head", something I've never been good at doing.

        THE NEXT THING I KNOW I sort of "woke up" and noticed that I was about FIVE FEET from the vehicle in front, both of us doing 70 mph!!! Nothing happened, everybody was just cruising along, but funny!!! (NOT) how you remember those things.

        I've worked all over the world on that damned old thing........all mobile. Hawaii on 75M at night, Spain and England, Germany. Down into S America, Japan, I don't remember where all. This was a few years where propagation REALLY opened up and in the last few cycles has not been duplicated
         
        Last edited: Jan 4, 2020
      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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        When I first got that mess going, I was trying to "tap" the loading coil for the "best match' (SWR). I had the radio locked in transmit, with the power turned down to minimum, and the swr meter propped up on the dash. I was out back trying to read the SWR reflected power through the back window, and "tap" the correct part of the loading coil with an alligator "clip lead" and a pin, poking into the coil turns.

        "RF BURNS"

        THE THING IS, loading coils and antennas can generate VERY HIGH RF voltages, even at low power settings. I "pulled an arc" off one finger, and the RF DRILLED A HOLE down into my finger, WHICH HURT LIKE HELL for WEEKS ON END!!!!!
         
      • Dave NEO

        Dave NEO Well-Known Member

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        vinyl bumper sticker or clear contact paper cut to size of base and stuck to the car (not to the magnet base). my experience with Wilson 500s is that no matter what you do if you leave it in place you will have some type damage after a few years.
         
      • yeswedeliver

        yeswedeliver New Member

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        Thanks to all of you - it is so cool that you all engaged - all were excellent thoughts, good ideas - and sound data ... I actually learned - better said, I was reminded, of the nature of 'connection' to the car. Finally, I am afraid the most recent experienced comment from Dave is the unwelcome truth ... to attach it and leave it - there is a cost in damage to the paint ... pretty much no matter what ... .
        No matter, I enjoyed all of your input. Thanks!
         
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        • pa340dart

          pa340dart Well-Known Member

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          @74DartSwinger360
          Found this during my dad’s cellar cleanout
          He was so into “ham radio”
          Old school since late 40’s
          >> drawback you have to drill 2 holes in the trunk gutter

          22A60889-F7B2-4F5D-8101-AAC8033006EB.jpeg

          93DA6BC7-FFD7-40FC-8AE4-7BC09424179B.jpeg
           
        • Mr. Sinister

          Mr. Sinister Devastation Manager

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          Put it on the nieghbors car.
           
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