Sealing back side of NMO mounts that are not used in a "through-panel" install?

[Sbsyncro]

So most people with Jeeps and trucks are not installing their NMO antennae in a "through the roof" mount and are instead using external brackets.  NMO mounts such as the "Midland 6 Meter Antenna Cable with NMO Connector" are obviously designed to be water proof (with an o-ring seal) when installed on a flat panel where the underside is protected from weather by the panel that it is mounted to and the o-ring on the top side of the panel.

In a bracket type mount, the underside of the NMO mount is completely exposed to the elements.  Is this a problem?  Should one somehow protect it from the elements?   Most installations I see just leave it exposed, so I wonder if the o-ring is merely to seal the roof panel from leaking and not to necessarily protect the back side of the antenna mount.

[kidphc]

Nmo weren't designed to have the back side exposed to the environment (weather).

I searched for a while and found water resistant ones but they aren't much different from the regular one in design.

My hood mount bracket, the nmo doesn't seal well on both sides.

I ended up pulling the plastic cover back, had to because the center pin broke connection. The manufacturer used hot glue to seal it up.

After soldering. I ended up using hot glue to quickly fill the cap on and pressed and clamped till set. I purposely used too much so it oozed out. Then covered the whole backside with water proof rtv silicone.

For the topside (way more then I normally use) I used a lot of conductive contact grease. You do not want to use to much or you will short the outer to inner. So some cleaning up is necessary.



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[BoxCar]

There are water resistant (close to waterproof) tapes available designed primarily for protecting the connectors. For the mount itself, I would flush it with 91% isopropyl alcohol and then use a good weather resistant caulk to seal the bottom or back side of the mount. A lot of the better caulks can be painted.

[Extreme]

Duct Seal, aka: bear shixx has worked for 2 years on the NMO exposed underside on my S x S.

For instance:  https://www.lowes.com/pd/Gardner-Bender-Duct-Seal-Compound-5-lb-Pugs/5001428173

[gortex2]

Most of us use the Larsen NMOKHFUD NMO Mount. It isn't 100% waterproof but way better than the others. I normally slip a piece of self sealing heat shrink over the cable and I have yet to have one get water in them. My JK is at least 10 years old and still works fine. They work really well.

https://www.theantennafarm.com/catalog/index.php?main_page=product_info&cPath=264_266_291&products_id=1125

 

[Extreme]

I run these because they require only a 3/8" hole instead of 3/4" and I can drill with a uni-bit + finish with 3/8" instead of a specialized hole-saw.  They're also available for different thickness mounting surfaces.   I don't know if they're susceptible to water intrusion but no issues for a couple years.  My rigs are garaged 90%.

https://www.theantennafarm.com/catalog/index.php?main_page=product_info&cPath=264_266_1291&products_id=1154

[gortex2]

The base of those is just like a standard NMO and open under the plastic. They will fill up with water in rain and wick into the cable. 

 

[Extreme]

The base of those is just like a standard NMO and open under the plastic. They will fill up with water in rain and wick into the cable. 
 

If exposed to the the elements I use Duct Seal.

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[widnerkj]

Liquid electrical tape would be what I would use.

Gardner Bender 07315001126 LTB-400 Liquid Electrical Tape, Easy-on, Waterproof, Indoor/Outdoor Use, 4 Oz. Jar, Black, Bottle https://www.amazon.com/dp/B000FPAN2K/ref=cm_sw_r_cp_api_glt_fabc_X3G6JWQ2174DCBF19FZB

[Guest]

On 5/27/2021 at 6:31 AM, kb2ztx said:

Most of us use the Larsen NMOKHFUD NMO Mount. It isn't 100% waterproof but way better than the others. I normally slip a piece of self sealing heat shrink over the cable and I have yet to have one get water in them. My JK is at least 10 years old and still works fine. They work really well.

https://www.theantennafarm.com/catalog/index.php?main_page=product_info&cPath=264_266_291&products_id=1125

 

 

I second this - same method and part number. Never fails.

[Doctnj]

I had to make a bracket to mount to roof top.  Used coax seal tape.  Damn good tape.  Uv resistant etc.  Don't know if you can see but there are several layers.  If I have to take it down.... Basically never, I'll have to cut tape off. Tape wrapped around bracket and feed line in a figure eight and upside down figure eight. 

[widnerkj]

Sort of reminds me of "rubber splicing tape"  we use in motor connections.  Seriously stretchy, only sticks to itself, is overall pretty fantastic to have in the toolbox.  Also called "mastic tape".

 

Here is a link of the good stuff.

https://www.amazon.com/3M-Scotch-Moisture-Sealing-Electrical/dp/B001B1AP3O/ref=psdc_256161011_t3_B0000CBJ5W

[Doctnj]

On 6/18/2021 at 9:53 PM, widnerkj said:

Sort of reminds me of "rubber splicing tape"  we use in motor connections.  Seriously stretchy, only sticks to itself, is overall pretty fantastic to have in the toolbox.  Also called "mastic tape".

 

Here is a link of the good stuff.

https://www.amazon.com/3M-Scotch-Moisture-Sealing-Electrical/dp/B001B1AP3O/ref=psdc_256161011_t3_B0000CBJ5W

Yeah that sounds like the same characteristics. Between the layers of this tape on the roll is mylar film to keep it from becoming a solid Puck. 

[overrulecaratmutt]

The PCTEL Maxrad MBM looks like it's sort of a surface-mount to their angle/mirror bracket, with the cable coming out the side of a housing. Does anyone know if these are actually weatherproof assemblies?

I ordered a Laird MB8 before realizing that the NMO is open on the bottom, will have to try the Larsen NMOKHFUD next.

 

[gortex2]

used alot of those maxrad mirror mounts on dump trucks over the years. As long as its assembled as the picture its waterproof. The bottom of the mount is open and if you remove the 2 screws from under the bracket that mount comes off and its wide open. We used to have to repair some that got water damaged after years on the vehicles. Alot of DOT/DPW vehicles ran those in the NE on trunk systems.

[widnerkj]

KB2ZTX,  If you were going full crazy in a waterproofing attempt.  I'd imagine you could go wild like on an aircraft fuel tank, and apply sealant to the screws from under, like rivets in a plane's fuel tank.  Though, even being a former Navy wire biter, this might be going too far.

 

https://shop.vansaircraft.com/cgi-bin/shop.cgi?browse=misc&product=proseal

[overrulecaratmutt]

Thanks for the clarification @kb2ztx! Sounds like the Larsen NMOKHFUD is still the way to go then.

ocm

[JCase]

I know I’m a little late adding my comments but, I discovered the same issue with the bottom not sealed. I filled the cavity with silicone and this remedied the issue. So far, so good. 

[maddogrecurve]

On 5/27/2021 at 3:31 AM, kb2ztx said:

Most of us use the Larsen NMOKHFUD NMO Mount. It isn't 100% waterproof but way better than the others. I normally slip a piece of self sealing heat shrink over the cable and I have yet to have one get water in them. My JK is at least 10 years old and still works fine. They work really well.

https://www.theantennafarm.com/catalog/index.php?main_page=product_info&cPath=264_266_291&products_id=1125

 

That's the one I have, I used an initial heat shrink tube, then spread silicon over that and shrunk another tube over that to really seal it.