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Reinforce rooftop NMO mount?

Discussion in 'On the Road' started by KK4JW, Oct 13, 2020.

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  1. KK4JW

    KK4JW Ham Member QRZ Page

    I have a roof mounted VHF 1/4 wave NMO antenna on my car and it works well. I'd like to upgrade to a 5/8 antenna which is obviously quite a bit longer and will obviously increase load on the mount at highway speeds.

    Providing my NMO is correctly installed with the proper size hole, etc (it is), would adding a very thin aluminum "backing plate" be beneficial or perhaps cause a RF ground contact issue with the rest of the vehicle?

    I don't want to do anything that would cause an issue - but at the same time, I want my antenna installation to be as solid as possible.
     
  2. K6CPO

    K6CPO Ham Member QRZ Page

    Any kind of reinforcing plate you decide to add isn't going to help one bit unless it's securely fastened to the metal surrounding the hole. Just securing it with the antenna mounting hardware isn't going add any more strength.
     
  3. KF5FEI

    KF5FEI Ham Member QRZ Page

    A larger washer would give you a bit more protection from flex, but you'll still have a smaller surface area on the outside. Even a 1/4-wave antenna will tear up a thin roof if it gets snagged. Body shop broke one off the wife's roof somehow -- and bent up the roof in the process -- while replacing the hood.
     
  4. AG6QR

    AG6QR Premium Subscriber QRZ Page

    Take a look at Breedlove antenna mounts, findable via your favorite search engine. My car has one of their 503 NMO roof mounts, and it has hefty hunks of machined aluminum both above and below the roof sheet metal. It's hard to imagine a sturdier NMO mount.
     
    KJ7AAI likes this.
  5. W9WQA

    W9WQA Ham Member QRZ Page

    need a plate inside and out. then its a water trap unless sealed good. is there room for 2 on the mount? could you get inside?

    oops didnt see above. 2 typing !!
     
  6. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    I’ve never experienced a wind loading problem on a mount from a tall 2m antenna (Low hanging branches, yes.) I wouldn’t worry about it.

    If there is a sizable risk of hitting something solid, like a garage door, drive-through roof, or branches, then get a quality flexible whip antenna from Laird/Larson which will likely take all the stress. Or just keep the 1/4 wave, which ideally should also be a flexible whip just in case.
     
  7. N1IPU

    N1IPU Premium Subscriber QRZ Page

    Had a Jeep Commando with the steel pop off top. Very flexible roof. My solution was a 4" 20ga. SS plate. Hole punched for the NMO and added a ground lug to one corner. I silver soldered it but you can just a s well drill and tap then cut the remain screw off the contact side of the plate. Used Araldite 300 hi temp adhesive after some roughing. Designed for aircraft structures so its a lifetime bond. It worked well and supported the antenna. Lot of work though so I will Second the breedlove mount. If he doesn't have what need on the website give him a call. He is very helpful for the one off mounting. I used his so-239 flat mount with 3"plates before. It's bulletproof. I use a 4" so-239 ball mount on the side of my truck to support a screwdriver and it's as tough as they come.
     
  8. AI7PM

    AI7PM Ham Member QRZ Page

    Is it a commercial grade 5/8 antenna? (Laird, Comtelco, Larsen, PCtel.....?) They don't really add any strain. If you are lookinfg at Comet, Diamond, or some of the ham grade stuff with the thick less flexible whips, maybe.
     

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