Question on mount types and strength

[Chazz Layne]

I was going to install a 2-meter in the wife's truck this afternoon, thinking it would be a simple task since a shop had already previously installed a CB and antenna (hole-in-the-roof type). I did make the mistake of ordering a NMO antenna and mount, which obviously swims in the hole for the larger UHF mount. No biggie, now it has a hole a few inches further back that is NMO-sized and we can add a CB later if needed. The trouble I ran into is when I went to put the mount on - when tightening it down I did so expecting what I would get from a CB antenna or UHF mount... make it nice and tight. The NMO snapped right in half at around what I'm guessing is 10 pounds of torque (not sure, since I wasn't using a torque wrench for the above reason). Diamond is supposed to be good stuff, so I'm guessing it is me and not the mount. This was also enough to bend the flimsy roof panel around the hole.

This leads me to a question of strength when it comes to putting a 33" antenna on thin sheet metal in an off-road vehicle. Should I be using the heavier duty UHF style mount and antenna for such a purpose? Also, what is the recommended torque setting for a NMO mount and an UHF mount? I now have holes for either and need to order a new mount/cable anyhow at this point so...

[cruiserlarry]

I was going to install a 2-meter in the wife's truck this afternoon, thinking it would be a simple task since a shop had already previously installed a CB and antenna (hole-in-the-roof type). I did make the mistake of ordering a NMO antenna and mount, which obviously swims in the hole for the larger UHF mount. No biggie, now it has a hole a few inches further back that is NMO-sized and we can add a CB later if needed. The trouble I ran into is when I went to put the mount on - when tightening it down I did so expecting what I would get from a CB antenna or UHF mount... make it nice and tight. The NMO snapped right in half at around what I'm guessing is 10 pounds of torque (not sure, since I wasn't using a torque wrench for the above reason). Diamond is supposed to be good stuff, so I'm guessing it is me and not the mount. This was also enough to bend the flimsy roof panel around the hole.

This leads me to a question of strength when it comes to putting a 33" antenna on thin sheet metal in an off-road vehicle. Should I be using the heavier duty UHF style mount and antenna for such a purpose? Also, what is the recommended torque setting for a NMO mount and an UHF mount? I now have holes for either and need to order a new mount/cable anyhow at this point so...

I've used Diamond NMO roof mounts in vehicles for years, with all types / lengths of antennae without issue. Most mounts should be tightened until snug - but not cranked tight. As far as torque specs, you'll probably need to e-mail Diamond.

I actually prefer the NMO mount on the roof, as it's lower profile, and a wider base on the antenna, than a UHF style mount.

Sorry you had a problem, but I'd give it another try with a gentler hand...

[Chazz Layne]

Will do, that'll save me the cost of another antenna too...



It is getting cold, wet and windy so for now... DUCT TAPE!

[sdnative]

I have two of these mounts on my roof, and I don't recall any trouble with the install. The bottom piece has two wings that press into the bottom of the roof. The top piece screws onto the post that pops up through the hole. It has an o-ring to make a weather tight seal. Just tighten so it is snug.

If you are installing the mount in a thin part of the roof (where there are no cross-supports, etc) it will not be able to support a heavy antenna, especially if there will be horizontal forces (wind during freeway driving, hitting tree branches, etc). I would only recommend short or flexible antennas for these mounts, and not the more rigid types like the half-waves. I had a diamond half-wave up there and bent the roof a little by hitting some low branches.

[BigDave]

..... so for now... DUCT TAPE!

Duct tape is my friend. That and safety wire.

[Chazz Layne]

If you are installing the mount in a thin part of the roof (where there are no cross-supports, etc) it will not be able to support a heavy antenna, especially if there will be horizontal forces (wind during freeway driving, hitting tree branches, etc). I would only recommend short or flexible antennas for these mounts, and not the more rigid types like the half-waves. I had a diamond half-wave up there and bent the roof a little by hitting some low branches.

I think I will reinforce it a little when I get the replacement mount in, I have plenty of scrap aluminum laying around from my other project. The only place thin enough for the mounting stud to go all the way through is this little island of REALLY thin stuff that was kind of scary to drill through (couldn't tell until I was suddenly through it).

[sdnative]

The only place thin enough for the mounting stud to go all the way through is this little island of REALLY thin stuff

Larsen makes a really nice THICK NMO mount that should go through even the thickest part of your roof. If you can drop the headliner some, you'll be able to find a nice spot. I had to do mine by feel.

See page 7 of this document:

http://www.larsen-antennas.com/docfiles/ASB8/Mounts.pdf

[DaveK]

I was going to install a 2-meter in the wife's truck this afternoon, thinking it would be a simple task since a shop had already previously installed a CB and antenna (hole-in-the-roof type). I did make the mistake of ordering a NMO antenna and mount, which obviously swims in the hole for the larger UHF mount. No biggie, now it has a hole a few inches further back that is NMO-sized and we can add a CB later if needed. The trouble I ran into is when I went to put the mount on - when tightening it down I did so expecting what I would get from a CB antenna or UHF mount... make it nice and tight. The NMO snapped right in half at around what I'm guessing is 10 pounds of torque (not sure, since I wasn't using a torque wrench for the above reason). Diamond is supposed to be good stuff, so I'm guessing it is me and not the mount. This was also enough to bend the flimsy roof panel around the hole.

This leads me to a question of strength when it comes to putting a 33" antenna on thin sheet metal in an off-road vehicle. Should I be using the heavier duty UHF style mount and antenna for such a purpose? Also, what is the recommended torque setting for a NMO mount and an UHF mount? I now have holes for either and need to order a new mount/cable anyhow at this point so...

The-sheet-metal-bending-in-the-trees thing is the major reason why I have my vhf/uhf antenna mounted to a sturdy reinforced mount on my roof rack. The other solution is to put a spring on the antenna so it will be better able to avoid damage from low branches, etc. There are some motorized units that will angle the antenna to a down position at the push of a button but since those !@#$ branches come out of nowhere, I prefer the spring (it reacts when I may not).

I have found the NMO mounts to be very strong and have never had one break. I seem to recall that Amphenol (sp???) makes some good quality mounts.

[Chazz Layne]

I finally got something resembling internets at the new place... still pretty pathetic though. I think I have a more stable/faster connection on my phone.

The new mount is here (the same Diamond NMO mount), going to install it hopefully tomorrow so we can see what the reception is like out here for Thursday's net. I *think* I might just have line-of-sight to Keller from the roof...

[unwiredadventures]

... make it nice and tight. The NMO snapped right in half at around what I'm guessing is 10 pounds of torque (not sure, since I wasn't using a torque wrench for the above reason). Diamond is supposed to be good stuff, so I'm guessing it is me and not the mount. This was also enough to bend the flimsy roof panel around the hole.

I've never tried Diamond. I've always used Comtelco NMO mounts. I've always used the model with the fully enclosed base (CEZM) and double shielded coax so I can use it for cellular, wifi, CB or Amateur Radio. I've abused them and tightened them quite tight. I've never had one fail.