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NMO Mounts and Wind Loading

jcrmadden

Member
Joined
May 10, 2024
Messages
182
Hello everyone. My name is Ray and I'm an Antennaholic.

Hello Ray...

It's been four days since my last antenna purchase.

**Scratches neck nervously**

Seriously, I have more antennas than I have underwear, and all but two are are on Breedlove QD's for a "quick fix"

The wife's Yukon still doesn't have a permanent mount, but I picked up a NMO27B and W640B in preparation (because why not).

"I can stop anytime I want! Okay?!"

Then I found the NMO to 3/8x24 adapter and why wouldn't I expand the antenna options (addiction) to both vehicles?

Antics aside, my real question is, "How much wind loading can an NMO mount really take?"
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
25,511
Location
United States
The wife's Yukon still doesn't have a permanent mount, but I picked up a NMO27B and W640B in preparation (because why not).

You'd want the NMO-34 coil if you are going to use the 64" whip, not the NMO-27 coil.

Then I found the NMO to 3/8x24 adapter and why wouldn't I expand the antenna options (addiction) to both vehicles?

Antics aside, my real question is, "How much wind loading can an NMO mount really take?"

Not sure anyone could accurately answer that since it will depend on the vehicle that its been installed on.

But, it'll have no issues running an NMO-27 at 80+ mph. Done that through Texas on an aluminum body Ford pickup.
Worst case, I had a stiff Larsen NMO quarter wave wide band antenna that has a very thick/stiff whip with a spring at the base. Got into a low clearance situation that resulted in the whip getting folded back 90º. Zero damage to the truck roof, zero damage to the NMO mount, spring took a permanent kink.

Properly installed NMO mounts are solid. Improperly installed, all bets are off.

Not sure I'd want to run a 3/8x24 antenna on there without a good spring. Most of those fiberglass antennas are not forgiving. And I'd not run a full 108" whip, either.

And I've done a lot of NMO mounts over the years, including lots on vehicles at work. Never had an issue with them with normal NMO mount antennas.
 

prcguy

Member
Premium Subscriber
Joined
Jun 30, 2006
Messages
16,637
Location
So Cal - Richardson, TX - Tewksbury, MA
Hi Ray, I can stop at any time too and probably attend meeting across town from you. Not that they are helping.

I've played with NMO to 3/8" adapters and they would be scary to use with most any fiberglass CB whip over 2ft or with a lightweight center load longer than about 3ft putting a lot of stress on the vehicle sheet metal. I use them on temporary base station adapters and for simply checking SWR on some antennas without actually driving around.

Do yourself a favor and buy another antenna, it will make you feel good as you ponder your final decision.
 

slowmover

Active Member
Joined
Aug 4, 2020
Messages
2,874
Location
Fort Worth
I once was running 90+ and easily 12-14k over gross in oilfield days leading a group westbound out of Galveston on the 600-mile drive to Monahans, TX. At about where the speed limit opens up to 80 on IH-10.

Almost had a heart attack when a DPS trooper was coming up alongside. He had to be at over 100-MPH.

I’d have noticed if any critters escaped from the antenna farm. Eagle-eyes, as I was waiting for him to pull over the bunch of us. To start the downshifts timed perfectly to plan:

It was gonna be tricky to come down s-m-o-o-t-h-l-y being that heavy and not get rear-ended . . . so as to not reveal how far over we were. Didn’t have the overweight permits for that part of the state.

Those AWD DODGE Chargers were speed-limited at either 140 or at the 155-MPH Autobahn limit. The early ‘70’s A38 DODGE Police Pursuit could cruise at 120+, but I can’t remember seeing NMO-type on them.

So git’er up past 90, drop it in the big hole and let it start that just perceptible side-to-side rock afore you check the mirrors to see what’s gaining on ye.


If he’s a’coming on that Dodge will still be up-and-down as long as he’s got his foot in it.

Frequency Shift Inbound.
.
 
Last edited:

slowmover

Active Member
Joined
Aug 4, 2020
Messages
2,874
Location
Fort Worth
I was running these on the Peterbilt West Coast mirror arms. Never worried about whip flex, but they were on BIG six-bolt, fully-threaded mounts.

That was the point where I’d added the DSP Speaker. Got out and back in excess of thirty-miles a few times once out near Fort Stockton.

Until you asked it, it hadn’t occurred to me to question whether an NMO34 + WD640 was in peril at 100-MPH.

.
 

prcguy

Member
Premium Subscriber
Joined
Jun 30, 2006
Messages
16,637
Location
So Cal - Richardson, TX - Tewksbury, MA
I once was running 90+ and easily 12-14k over gross in oilfield days leading a group westbound out of Galveston on the 600-mile drive to Monahans, TX. At about where the speed limit opens up to 80 on IH-10.

Almost had a heart attack when a DPS trooper was coming up alongside. He had to be at over 100-MPH.

I’d have noticed if any critters escaped from the antenna farm. Eagle-eyes, as I was waiting for him to pull over the bunch of us. To start the downshifts timed perfectly to plan:

It was gonna be tricky to come down s-m-o-o-t-h-l-y being that heavy and not get rear-ended . . . so as to not reveal how far over we were. Didn’t have the overweight permits for that part of the state.

Those AWD DODGE Chargers were speed-limited at either 140 or at the 155-MPH Autobahn limit. The early ‘70’s A38 DODGE Police Pursuit could cruise at 120+, but I can’t remember seeing NMO-type on them.

So git’er up past 90, drop it in the big hole and let it start that just perceptible side-to-side rock afore you check the mirrors to see what’s gaining on ye.


If he’s a’coming on that Dodge will still be up-and-down as long as he’s got his foot in it.

Frequency Shift Inbound.
.
In the mid to late 70s I worked at a CB/car stereo shop in Colorado Springs and had to go to a radio convention in Denver for CB stuff once. A friend drove me in one of these Smokey and the Bandit things and we stuck a new Turner mag mount CB antenna on the roof between the T tops and did about 125mph most of the way from north Colorado Springs to Denver and the mag mount was fine. Turner was one of the vendors at the show and after telling them about our trip it became part of the sales pitch for their mag mount antennas.

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