Short 800 MHz Antenna Won't Fit on NMO

[radiochuck]

I just got a new Tram 1128 800 MHz NMO antenna and the cavity under the threads at the base of the antenna isn't deep enough to fit on my NMO mount. In other words, I can't get the threads started because this antenna sits too high on the NMO's center 'nub.'

My other antenna has a deeper cavity with a spring loaded center contact, so it fits just fine. I'm not sure what I can do with this one, short of putting a 3/8 x 1-1/2 rubber washer under the threaded outer ring of the NMO mount. I'd rather not go that route, if there's another option. Looking for suggestions. Thanks!

 

[ramal121]

Thin flimsy metal in todays vehicles really allows the NMO center to come up higher than I ever remember before. The more you crank on it the higher it goes. Makes putting on those quarter wave whips a challenge.

Here's what I do. Put the antenna square on the mount and then press down hard. Turn the antenna nut counter clockwise until you feel/hear a click. This is the start of the threads lining up to each other and falling into place. Still pressing down now turn the nut clockwise and the threads should start. Finger tight only on that nut. Do not wrench it down to the car body otherwise you will probably crack that plastic piece at the bottom of the whip. No bueno. Good luck!

 

[mmckenna]

I just got a new Tram 1128 800 MHz NMO antenna and the cavity under the threads at the base of the antenna isn't deep enough to fit on my NMO mount. In other words, I can't get the threads started because this antenna sits too high on the NMO's center 'nub.'

My other antenna has a deeper cavity with a spring loaded center contact, so it fits just fine. I'm not sure what I can do with this one, short of putting a 3/8 x 1-1/2 rubber washer under the threaded outer ring of the NMO mount. I'd rather not go that route, if there's another option. Looking for suggestions. Thanks!

I'm not a fan of those "chrome nut" type antennas. I've found that water will eventually find its way down inside and causes corrosion. Usually down past the whip. I would not use one of those if the base doesn't seal down properly. I think it's asking for issues.

Some NMO mounts stick up a bit higher when you tighten everything down, like what Ramal said. If you can get the threads to engage well enough to hold the antenna, adding the gasket might do what you want. However, if you have an antenna that works better, why not just go with that?

 

[devicelab]

Press down hard.

This phrase works for a lot of things but particularly NMO antenna mounting.

PS. You should always have a rubber ring at the base of the NMO mount or as Matt says you'll get water ingress. Some antennas have one integrated with their base but an extra one isn't a bad thing as long the antenna works!

 

[radiochuck]

Put the antenna square on the mount and then press down hard.

That did the trick. Lol.

Thanks for all of the suggestions.

 

[radiochuck]

I'm not a fan of those "chrome nut" type antennas.

There weren’t a lot of great options for a low-profile 700/800 MHz mobile antenna, so I settled for this one.

 

[mmckenna]

There weren’t a lot of great options for a low-profile 700/800 MHz mobile antenna, so I settled for this one.

It's just a 1/4 wave.
I use these at work because of the much better sealing design on the base:

Larsen NMOQ800B 806-896 MHz Mobile Antenna NMO Type 4.5"

Larsen NMOQ800B 806-896 MHz 1/4 Wave Mobile Antenna - NMO - Black

theantennafarm.com

I've recently started using EM Wave antennas, which I've found to have an even better base seal:

EM Wave EM-MX0746 746-894 MHz 1/4 Wave Mobile Antenna - Stylish High-Impact Dual Shot Xenoy™/TPV Base - NMO

EM Wave EM-MX0746 746-894 MHz 1/4 Wave Mobile Antenna - Stylish High-Impact Dual Shot Xenoy™/TPV Base - NMO

theantennafarm.com

 

[radiochuck]

It's just a 1/4 wave.
I use these at work because of the much better sealing design on the base:

Larsen NMOQ800B 806-896 MHz Mobile Antenna NMO Type 4.5"

Larsen NMOQ800B 806-896 MHz 1/4 Wave Mobile Antenna - NMO - Black

theantennafarm.com

I've recently started using EM Wave antennas, which I've found to have an even better base seal:

EM Wave EM-MX0746 746-894 MHz 1/4 Wave Mobile Antenna - Stylish High-Impact Dual Shot Xenoy™/TPV Base - NMO

EM Wave EM-MX0746 746-894 MHz 1/4 Wave Mobile Antenna - Stylish High-Impact Dual Shot Xenoy™/TPV Base - NMO

theantennafarm.com

I’m not very knowledgeable when it comes to antennas. I’m much better at programming the radio than I am when it comes to the technical workings of the antenna.

The EM Wave looks like a much better antenna, though. I’ve ordered one and will probably send the other back to Amazon.

 

[madrabbitt]

like he said, and like i've agreed to in several other related posts.

The EM Wave is probably the best sealing NMO. its all i'm using on my POV, its what i've been switching agency vehicles to (except the ones where we had the stupid $200 STI-Co)

Their quarterwave that you ordered is a really good antenna, using them on a bunch of fleet vehicles.

 

[radiochuck]

Their quarterwave that you ordered is a really good antenna, using them on a bunch of fleet vehicles.

It was delivered to my office yesterday while I wasn't there. I'll get it today and give it a try and report the results. Thanks again for everyone's input.

 

[OpSec]

It was delivered to my office yesterday while I wasn't there. I'll get it today and give it a try and report the results. Thanks again for everyone's input.

You should be successful. Our entire fleet is E/M-Wave, which is around 1600 antennas total.

 

[madrabbitt]

get a tiny thing of dielectric grease at the auto parts store. Put it on the rubber ring and its groove (and it will probably fall off once you install it) and on the inner threads. Tighten the base as far down on the NMO mount as possible and leave it.

Then, separate the antenna at the middle, put some dielectric on the silver threads, and screw the nut and attached whip back.

For car washes, remove just the nut and whip. leave the base in place. Its a better seal then even those car wash caps.

 

[radiochuck]

Yeah, that ring is a little weird. I do need to put some grease in there. It’s good for the moment.

Antenna is great tho. Love the small form factor and great reception.

I don’t know how I ever survived using a Remtronix antenna INSIDE the car. LOL.

 

[mmckenna]

Yeah, that ring is a little weird. I do need to put some grease in there. It’s good for the moment.

It's much easier to just put it down over the NMO mount first, then screw the antenna down.
Even if you use the grease, it's going to stay there when you unscrew the antenna.

 

[radiochuck]

It's much easier to just put it down over the NMO mount first, then screw the antenna down.
Even if you use the grease, it's going to stay there when you unscrew the antenna.

The thing is, I do plan on changing antennas from time to time. For instance, when I drive to California next weeekend, I'll be swapping the stubby antenna for the whip, so I can monitor CHP on VHF low. Maybe a few dabs of Emler's glue would be helpful to keep the ring in place. I'll have to fiddle with it over the weekend and see what I can come up with. It's secure for now, though.

 

[mmckenna]

The o-ring is still removable if you place it over the NMO mount first. You don't want to use glue as the o-ring will bind up when you tighten down the antenna and likely damage/tear it. No need to make this difficult.

When you remove the antenna to install a different one, just take the o-ring off and put it over the whip so you don't lose it. Truth is, the o-ring doesn't play that much of a role in keeping the moisture out. The base design does a pretty good job of that.

 

[radiochuck]

The o-ring is still removable if you place it over the NMO mount first. You don't want to use glue as the o-ring will bind up when you tighten down the antenna and likely damage/tear it. No need to make this difficult.

When you remove the antenna to install a different one, just take the o-ring off and put it over the whip so you don't lose it. Truth is, the o-ring doesn't play that much of a role in keeping the moisture out. The base design does a pretty good job of that.

Good point about the binding up if I were to glue it.

And honestly, I still have the rubber washer that sits round the outer diameter of the NMO mount, so the o-ring is pretty much redundany anyway. I can't imagine any moisture is getting in there, even without the ring.

 

[mmckenna]

Good point about the binding up if I were to glue it.

And honestly, I still have the rubber washer that sits round the outer diameter of the NMO mount, so the o-ring is pretty much redundany anyway. I can't imagine any moisture is getting in there, even without the ring.

You'll want to remove the rubber washer before installing the EM Wave antenna. The only place those rubber washers belong is under the chrome nut style 1/4 wave antennas.

 

[bharvey2]

I just pulled all of the RF stuff out of a decomissioned fire truck. There were a number of the chrome nut style antennas (maybe 1/2 dozen) and every one of the NMO mounts showed signs of water intrusion and corrosion. While I fancy the NMO mount, I haven't doen much with those antennas. Seeing what I did, they sure wouldn't be my first choice. I P.M. my personnel vehicle antennas about anually (also NMOs) and haven't seen that problem.

 

[mmckenna]

Yeah, I've had a few of those chrome nut style antenna leak a bit of water down around the whip eventually and it can make a mess. I've been swapping ours out with the Larsen NMOQ antennas, but as soon as I run out, I'm going to switch to the EM Wave.