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Care of magnet mounts, and then some.

Discussion in 'Ham Radio - CB - Trail Communications' started by The DB, April 18, 2012.

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  1. The DB

    The DB Active Member

    June 14, 2011
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    City, State:
    St. Louis
    Year, Model & Trim Level:
    2000 Limited SOHC
    I went back all 36 pages and if a thread on this exists I must have missed it. I know I've seen parts of it mentioned on this forum before but most of it is buried in random threads.

    So you bought your new shiny new magnet mount antenna, put it on your roof, tuned it, and now you are done right? Not quite. You could do it that way, but you will have rust on your roof under that magnet, likely much sooner than you think.

    Stuff can still get in between the magnet and your vehicle like dust and water.

    Now dust can be near anything, tiny particles of random impurities in the air. When the roads are treated for snow this often includes some very corrosive chemicals. Some of this dust is even magnetic, and can ride the magnetic field and cause circular scratches in your paint eventually causing rust patterns. You likely won't even see it on the magnet or the roof under the magnet if you take the antenna off and look unless a lot has built up.

    Contrary to popular belief, rain water is not pure water. It is called acid rain for a reason, and pretty much all of our rain has some acidity.

    When these two separate issues combine a chemical reaction can happen, creating a mild sulfuric acid that will over time eat away at your paint. In addition, scratched paint plus the corrosive chemicals from ice melt in winter will quickly cause rust.

    It is best to clean under the magnet, and the roof of the vehicle where the magnet rests. I like to recommend at least once a month, although the more often the better. Just after it rains is always a good time, before any chemicals have a chance to do any serious damage to your paint as it takes much longer for the area under the magnet to dry than the rest of your vehicle.

    You might also consider moving the antenna when cleaning it. It doesn't have to be far, just not exactly where it was. Moving it between two or three positions can have a long term effect keeping issues from happening. Just be sure you clean both where the antenna was and where it is going on the roof.

    You may be surprised to hear that these antennas don;t always stay in one place by themselves. If the antenna is moving around when driving it needs a larger magnet than it has. Even if it is not moving around, the only thing holding the antenna in place is a magnet. As your engine runs and you drive down the road and hit bumps and such the body of the vehicle is vibrating, and some of these vibrations are larger and more sudden than others. This can also cause a wearing of the paint on the roof.

    I also should point out that most magnet mount antennas have a film at the bottom of the magnet. Most people think it is to help protect the vehicle, and that is true. Some antennas use this magnetic connection as part of the tuning network, and removal of this film (even just breaking it) can cause SWR issues. That being said, replacing the film will usually fix any issues caused by breaking/removing this film. I know you can get the Wilson film by itself for about $5 if you look for it.

    As an information note, more or less for completeness, magnet mount antennas are less efficient than a properly set up permanent mount antenna. This is because you don't have a direct connection to the ground plane. They use a magnetic field and something called capacitive coupling. Different magnets used can vary the efficiency loss, but as a general rule, the larger the magnet (or combined magnets if you have a multi-magnet mount) the less efficiency loss you will suffer.

    That being said, the big magnet mounts that contain three and four magnets often become more like a permanent setup. And with their cost its often just as cheap if not cheaper to just install a permanent mount in its place. Plus it is very difficult to get them off for cleaning under the magnets.

    The DB
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