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Thread: Mobile antenna mount question

  1. #1

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    Default Mobile antenna mount question

    I've mounted a 2 meter antenna on my car fender and am looking for a little grounding advice. Since the antenna bracket is screwed directly to the fender with 3 sheet metal screws, is it advisable or not worth the time to run a secondary ground strap to the antenna bracket? Thanks for your help. :o)

    edit: The self tapping screws and L bracket mount are stainless and I have added a ground strap as well. Better safe then sorrry I always say.
    Last edited by KI7UJM; Thu 29th Mar 2018 at 01:58.

  2. #2

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    I can't quite picture the bracket being screwed to the fender, probably a US difference, as our wing mounts rarely screw on? However, as mag mounts don't have a direct ground connection, and performance isn't compromised to any great degree, I doubt an extra ground path is really worthwhile. My experience suggests that your performance will be more based on exactly where it goes and how distorted the polar plot is by being offset from dead centre of the roof.

  3. #3

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    You will be all good till a little corrosion sets in and then all bets are off. I would recommend stainless fasteners and toothed washers to help ensure a decent bond. Check this website out, tons of good stuff for mobileering and worth the time it will take to sift through and absorb it all. The info within works great on both sides of the pond.

    http://k0bg.com/

  4. #4

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    Default Thanks

    Quote Originally Posted by WZ7U View Post
    You will be all good till a little corrosion sets in and then all bets are off. I would recommend stainless fasteners and toothed washers to help ensure a decent bond. Check this website out, tons of good stuff for mobileering and worth the time it will take to sift through and absorb it all. The info within works great on both sides of the pond.

    http://k0bg.com/
    Totally awesome website, thanks! I'm going to spend a lot of time reading it.

  5. #5

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    Quote Originally Posted by KI7UJM View Post
    I've mounted a 2 meter antenna on my car fender and am looking for a little grounding advice. Since the antenna bracket is screwed directly to the fender with 2 sheet metal screws, is it advisable or not worth the time to run a secondary ground strap to the antenna bracket? Thanks for your help. :o)

    edit: The self tapping screws and L bracket mount are stainless and I have added a ground strap as well. Better safe then sorrry I always say.
    That's not the type of ground we are talking about.. What do you think a thin little copper ground strap is going to do?

    What we are talking about when we talk about RF is GROUND PLANE - AS IN THE MISSING HALF OF THE DIPOLE ANTENNA..

    A DIPOLE ANTENNA IS THE ONLY RESONANT ANTENNA. THINK TEETER TODDER, WHEN ONE HALF IS NEGATIVELY CHARGED, THE OTHER HALF IS POSITIVELY CHARGED. RF IS ALTERNATING CURRENT. BECAUSE OF SKIN EFFECT, SINCE THE PAINT ON THE ROOF OF A VEHICLE IS ONLY A COUPLE OF MICRONS THICK.. A MAGNETIC MOUNT ANTENNA CAN CAPACITIVELY COUPLE TO THE BODY AS LONG AS THE WAVELENGTH IS SHORT ENOUGH.

    TRY IT ON 10 METERS WITH 100 - 500 WATTS, AND YOU JUST MIGHT FIND A BURNED SPOT IN THE PAINT BENEATH THE MAGNET MOUNT...

  6. #6

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    That is the point - we are talking about VHF and above and at the point close to the feed, the current flow is greatest, but the voltage least - so any arcing needs voltage to initiate, which that close to the feedpoint doesn't exist. You could get arcing at the tip, but there the current is low. So the upshot at VHF and above is that the physical distance between the feed point and the metallic roof is too far to cause arcing. We need to be realistic here, and not use flawed physics in this way.

  7. #7

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    Quote Originally Posted by WZ7U View Post
    You will be all good till a little corrosion sets in and then all bets are off. I would recommend stainless fasteners and toothed washers to help ensure a decent bond. Check this website out, tons of good stuff for mobileering and worth the time it will take to sift through and absorb it all. The info within works great on both sides of the pond.

    http://k0bg.com/
    Thank you WZ7U for the web site. Much appreciated. I read some about ground plane and I see I have much too learn. Guess that's why they call me a nubie. :o)

  8. #8

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    No sweat sir, that's just another service I perform; pointing people to places way smarter than I. You think this is a lot; wait till you get the HF bug. Then it starts getting very hairy! You'll do fine if you just don't get in any hurries and not follow through properly. It's not rocket science, but it is science nevertheless. Enjoy the road, be safe and keep learning.

    Oh, I would probably lose the self tapping screws and splurge for stainless screws with nuts and washers. Realize that it could require removing some sheet metal or fender skirts to access tight spots, that's where the planning phase is critical. I remember when I put my first antenna bracket on (I'm betting nearly identical to yours) I planned for weeks how I was going to pull it off. I also learned a little about how my pickup was put together during that exercise and the really sad part was that in less than a year I wasn't using the antenna anymore because thieves decided I didn't need to operate mobile and I have yet to replace that 2 meter radio after nearly 20 years. I hope YMMV.

    73, Eric wz7u
    Last edited by WZ7U; Fri 30th Mar 2018 at 06:33.

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