NMO Mount angle

Discussion in 'General Technical Questions and Answers' started by N1DVJ, Jul 10, 2009.

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  1. N1DVJ

    N1DVJ Ham Member QRZ Page

    I'm about to drill my Mustang to put an NMO mount on the small strip in front of the trunk and before the convertible well. There's not much of anywhere else to mount an antenna that won't really detract the looks of the car. I can't use a trunk lip mount because the trunk goes 'past vertical' when it's opened.

    The only catch is that the trunk STILL goes up and hits the antenna. (I have a mag mount sitting there now, so I know how much it hits.) I'm willing to put up with a slight hit with my Larson Kulrod, which has a small base coil and then a thin whip, but if I put my Diamond dualband on, I'm afraid it would really be a conflict.

    Anyway, I was thinking... (Step back!!) If I had a small 'wedge' that I could put there. Something that would give the NMO mount just a few degrees of 'tilt' to the front, everything would clear.

    Are there any commercial products to do this?

    Mike N1DVJ
  2. NE3R

    NE3R Ham Member QRZ Page

    not sure of a commercial product, but from your description, I would first worry about the integrity of the mount and making sure water doesn't get in there.

    I'm not sure of the antennas you are using, but in any case, straight up and down would be ideal. Do you think bending the actual antenna element slightly would work?

    73 de Joseph Durnal NE3R
  3. N1DVJ

    N1DVJ Ham Member QRZ Page

    With the Larson Kulrod 5/8 antenna it's not an issue. It's a THIN whip, and the coil base for the thing is pretty stubby.

    However, the Diamond (I think it's the 660 model) has a 'disk' at the bottom that screws over the NMO mount, then a vertical coil that's a number of inches tall, then a mechanism to allow for 'pull and tip-over' that's kind of neat. Unfortunately from the base to the point where it tips over is probably over 6 inches, and definately into the space the truck tries to occupy when open.

    As I said, the trunk goes 'past vertical', so I can't mount on the trunk, or I'd surely be breaking the real window in short order!

    As to weather-proofing... If the angle base was made of a material that would seal... But I suspect that I'd have to do the 'wedge' on both the top of the body and underneath on the bottom, otherwise the 'ring' of the NMO may not seat and seal correctly. Just have to see, I guess. I may take a piece of sheet steel and see what I can fabricate.

    Mike N1DVJ
  4. KB1JUF

    KB1JUF Ham Member QRZ Page

    Another option might be to limit how far the trunk lid opens with a piece of rope from inside the trunk. If you need to open it fully only once in a while, unscrewing the antenna from the NMO and a d ring shackle in the center of the rope will give reasonably quick access.
  5. N1DVJ

    N1DVJ Ham Member QRZ Page

    The rope might actually be a good idea. But I'd hate to rely on it if failure meant damage. Rope has a way of 'loosening up' at the worst possible time!
  6. K8JD

    K8JD Ham Member QRZ Page

    Why don't you park the Mustang and put a cover over it and just drive it on Sunday, Get a Beater like an Escort or an older Focus for everday driving and load it with VHF, UHF on the roof and HF antenna on the trunk lid. :D
    Problem solved..............
  7. N1DVJ

    N1DVJ Ham Member QRZ Page


    I'll run right out and buy a new car!
  8. KF6NFW

    KF6NFW Ham Member QRZ Page

    I dont think you mentioned the year of "horse"! May sound trivial, but to get better response it could be usefull for us to be able to look at either a pic or the real thing to understand your delima better.

    While not much of a stang, I had a 79 that I put a through hole mount on the trunk lid as well. of course I didnt have to worry about convertable tops.
    I did however have to make sure to mount as far to the back as possible and keep integrity to clear the back window and top of the car, otherwise I had several dings left behind from the whip hitting and vibrating when opening the trunk.

    As for a sealant, I would suggest some RTV. I had to use some when I did my through hole mount because I had to also install a re-enforcement plate to take up the flex in the trunk lid. I was afraid of ripping it out. I installed a 1/4 inch plate about 12 inch diam. on inside of trunk, with a 1/8 x 6 inch on the top to fix the problem. but I was left with a problem of the water getting in. I tried collars and other tricks and couldnt get anything to really work long term. I resulted to some KY jelly as an experiment, and was actually impressed with the reults, but of course it does wash off over time, as well as drips when heated by the CA. sun in summer.
    I finally had enough and went for the RTV. with a beer in hand and a week to get it right, I took my time and applied a VERY thin coat to the underside of the top plate, cleaned up with a thin bead all the way around the disk. once it was all dry, I masked off and painted the damn thing to match the color of the car. Of course this was when cars actually had metal for a body and not plastic and fiberglass!

    When it was all done, it was water tight, PERMANENT, and the best of all, the wife was happy with it!

    Your idea of using a shim or some sort of angled k in place will work but you will have to use the same on both sides of trunk lid as in top and bottom, otherwise as you noted the NMO will want to move to a loose position, and cause failure.
  9. N1DVJ

    N1DVJ Ham Member QRZ Page

    Sorry about that... It's a 2006 Convertible.

    At first I was worried about the thickness of the cavity where I'd have to mount it, but that now seems to be the least of my worries.

    Now I suspect I can cut a small access hole from inside the trunk. And them maybe even a complete access cutout under the area for the mount.

    And yes, I did consider the angle affecting integrity. But at least on the NMO mount that I have, the 'under panel' portion of the mount is a 'rocker', not something that would require the thickness to be the same all around. But still I don't think I want to leave it more than a little off from 'parallel' from the top surface to the bottom.

    What I'm thinking nowis to find a 'wedge' piece of hard plastic that I can cut to a 'square' the just barely is bigger than the diameter of the NMO top, and I want it to be down to a razor thin edge on the front edge. Then I think less than 1/8" inch on the back will be enough.

    Hmm, perhaps I should post some photos...
  10. KB0YYO

    KB0YYO Ham Member QRZ Page

    Or you could make a metal bracket to go from under the rear bumper brace ( bracket mounts to frame) up the side of the rear fender and mount the antenna on it and no holes in a new stang. Paint to match car color.
    It works on Pick up trucks and car owners that do not wish to punch holes in their car. Simple, cheap. and can be moved to another vehicle in case you wish to buy a Chevy.

    I cringe just thinking of drilling holes a Stang.

    By the way. Why does the antenna have to be on the rear?. Tradition? You could put on a trunk lip mount on the hood and you don't open the hood often but you do have a lot more clearance and the antenna just might not hit the roof . just a suggestion or two.
    Best of luck. No holes is best.
    Every hole is a beginning place for rust to start.
    for me. Drilling a hole is last resort with no other options left.
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