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NMO Externally Mounted

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Project25_MASTR

Millennial Graying OBT Guy
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Out of sheer curiosity, you think it’s strong enough to handle pulling into and out of a garage that only has about 6” roof clearance? I’m wondering if I’m just going to be stuck storing an antenna behind the back seat and manually replacing a rain cap if I want to use the radio.

I'm going to add to @mmckenna's reply. I run nitol antennas on my pickup (live in Texas, doesn't get cold enough to make them limp) which is tall enough that it is actually two inches too tall to fit in my garage (fits in every parking garage in Texas though). Actually, my garage is so low I drag whip on my Jetta with it's 1/4 wave VHF whip. Somewhere on Youtube there is a video of me driving through a parking garage in Lubbock averaging 10 mph slapping a Sti-Co Flexiwhip on the upper portions of the garage (last time I counted it was something like 53 strikes), you wouldn't know that antenna had been though that.

The only problem I've ever had was with a Comet CA-2x4SR. Struck a tree branch 20" above the roof and it mount came out of the roof. Been Larsen, Sti-Co, Laird and Panorama ever since and that was some 250,000 miles ago.
 

krokus

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The only problem I've ever had was with a Comet CA-2x4SR. Struck a tree branch 20" above the roof and it mount came out of the roof.

I had one of these antennas, and while it performed well, it being impacted did "interesting" things to the roof of my XJ body Jeep Cherokee. (This was before the spring section model was available.)
 

Project25_MASTR

Millennial Graying OBT Guy
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I had one of these antennas, and while it performed well, it being impacted did "interesting" things to the roof of my XJ body Jeep Cherokee. (This was before the spring section model was available.)

It came out the month after the incident happened. That was not on y XJ though...it was on my Trailblazer.
 

kb4mdz

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Cary, NC
Out of sheer curiosity, you think it’s strong enough to handle pulling into and out of a garage that only has about 6” roof clearance? I’m wondering if I’m just going to be stuck storing an antenna behind the back seat and manually replacing a rain cap if I want to use the radio.

Can verify that antenna length and a garage door height are critical values. Setup: Dodge minivan. Door height: 8 ft. Antenna: VHF/UHF dual-band, with spring, in a professionally drilled 3/4" hole smack in the middle of the roof. Well, I was working in the bidness when I did it.

When I installed it I said "Always remember to close the garage door after you pull in, so you release the antenna. Always remember that."

Always did, until one evening I was in a rush to go somewhere after dinner with the DD. Hopped in, started up, into reverse-go... hellacious noise!!!

Yup, backing up into the direction the antenna was already pointing. Ripped the ears right off the NMO mount as it got extracted from the roof. Oy vey.

probably woulda been OK if i'd just had simple quarter-waves on VHF & UHF; it doesn't matter now, I don't park in that side of the garage anyway. And another lesson in Never depend on yourself always being smart enough to...
 

Firekite

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I've since switched back to the standard Larsen NMOQ without the spring. The whip is flexible enough to take the hit.
Silly question I can’t seem to find a clear answer to: I realize this is billed as a 1/4 wave VFH/UHF antenna, but does it function as a monobander on ONLY one or the other, depending on cut length, or does it work reasonably well as a dual-band transmit antenna on both bands for a single dual-band mobile radio? I know you’re an advocate of using multiple monoband antennas with a diplexer, and I may got that route one day, but right now I’m trying to keep things simple.

Can verify that antenna length and a garage door height are critical values.
Right now the garage door allows only an inch or two clearance over the cab lights on my F250 (and thankfully is just deep enough to fit even with full replacement Ranch Hand bumpers front and rear). It’s frustrating because the actual garage ceiling is a legit 10’ or more (haven’t measured yet for exact height), but the door opening itself is only as tall as it was built in 1971. Maybe one day if I have the money I’ll come in and open it up higher.
 

mmckenna

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Silly question I can’t seem to find a clear answer to: I realize this is billed as a 1/4 wave VFH/UHF antenna, but does it function as a monobander on ONLY one or the other, depending on cut length, or does it work reasonably well as a dual-band transmit antenna on both bands for a single dual-band mobile radio? I know you’re an advocate of using multiple monoband antennas with a diplexer, and I may got that route one day, but right now I’m trying to keep things simple.

It's a "field tune" antenna, so it'll be advertised as something like 136-512MHz. When you buy it, it includes a cutting chart that gets you close enough to specific resonate frequencies.

Like many antennas, it'll resonate on odd quarter wavelengths of other bands, so while it's considered a mono-band antenna on the frequency you cut it for, they'll do OK on —some— other frequencies. I've used them quite successfully as dual band antennas, 2 meters and 70 centimeters. I ran one for years on a Yaesu FT-7800 dual band radio. The radiation pattern isn't "ideal" for all applications on 70cm if you cut it for 2 meters, but it worked just fine for me. SWR was low on both 2 meters and 70cm. Below 1.3 across the band on both.

Right now the garage door allows only an inch or two clearance over the cab lights on my F250 (and thankfully is just deep enough to fit even with full replacement Ranch Hand bumpers front and rear). It’s frustrating because the actual garage ceiling is a legit 10’ or more (haven’t measured yet for exact height), but the door opening itself is only as tall as it was built in 1971. Maybe one day if I have the money I’ll come in and open it up higher.

So, 3 or 4 inches above the roof? I think you might have issues. That's a little low.

I'm lucky enough that my truck doesn't fit in the garage.
 

Firekite

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The radiation pattern isn't "ideal" for all applications on 70cm if you cut it for 2 meters, but it worked just fine for me. SWR was low on both 2 meters and 70cm. Below 1.3 across the band on both.
That sounds like it would probably be good enough for me, then. I’m not sure how the radiation pattern would be affected or what applications would be less than ideal, but that SWR sounds good to me. One day I’ll need to get a good tuner, but hopefully I’ll be able to borrow one from someone when the time comes.

So, 3 or 4 inches above the roof? I think you might have issues. That's a little low.
Maybe. We’ll see I guess. Right now I can’t pull into the garage due to all the stuff in it as we finish renovations before moving in. But once I can at least pull most of the way into it, I’ll see what the actual clearance is once I reach the middle of the roof. When test fitting before purchase, I pulled the mag mount with the NMO2/70SH off the top.

I'm lucky enough that my truck doesn't fit in the garage
That would make it easier to ignore garage issues. But we get some bad hailstorms around here from time to time, and the new place sits immediately on a main public road. With Super Duty trucks being so popular to steal, and tailgates being popular to steal, and being so easy to break into them for any opportunistic passers-by, I’d rather go ahead and pull the antenna off if it comes to that.
 

mmckenna

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That sounds like it would probably be good enough for me, then. I’m not sure how the radiation pattern would be affected or what applications would be less than ideal, but that SWR sounds good to me. One day I’ll need to get a good tuner, but hopefully I’ll be able to borrow one from someone when the time comes.

On VHF, the radiation pattern is nice and round with good radiation out to the horizon and above.
On UHF, the radiation pattern, from my understanding, goes a bit high.

That might impact long distance coverage on UHF, but where I live with lots of hills and mountains, long range UHF involves repeaters.

The nice thing about 1/4 wave antennas is that they are quite broad banded. Cutting to the included cutting chart gets you pretty dang close in my experience. I've got some high end test gear at work and can analyze antennas, and I've found that the cutting charts do well.

Here's a plot from the VHF quarter wave on my truck. Notice perfectly acceptable SWR from 144 to up above 174.

qlfXD2a.jpg
 

nzoliver

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Christchurch, New Zealand
The biggest issue I have with mounting it though the body panel here is this is on our camping vehicle. Even with the best of intentions we have had an antenna snag a tree and get ripped off. Its much easier to make a new bracket than have a buckled/ripped body panel. Maybe for this setup it would have made more sense to use an SO-239 connector.

I think for the time being I'm going to swap to one of the heat shrunk / crimped versions of the NMO base and see how it holds up. It looks like I can get those with ATX195 coax or RG58A/U. Since my run is only 3ft in length I'm thinking the difference in loss is negligible and getting the RG58A/U with the solid PE dielectric vs the ATX195 with a foam PE is going to be my best foot forward with regards to bend radii / conductor migration? Is that correct thinking?

Hi

Worldwide SO239 connectors are used a LOT. They are waterproof if you get the correct ones from good manufacturers like Diamond etc. I have had SO239 connectors on pretty much all my radio gear for over 10 years running 50w at VHF and UHF and I've lived in some very harsh environments and I've never had any issues at all with water ingress from snow or rain. Dirt stays out too. I've seen lots of SO239 mounts come out of Japan on vehicles and they might look a bit iffy on the outside but the connection with the antenna off was perfect.
My 10c

Oliver
ZL3OOC
 

KK6ZTE

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That sounds like it would probably be good enough for me, then. I’m not sure how the radiation pattern would be affected or what applications would be less than ideal, but that SWR sounds good to me. One day I’ll need to get a good tuner, but hopefully I’ll be able to borrow one from someone when the time comes.


Maybe. We’ll see I guess. Right now I can’t pull into the garage due to all the stuff in it as we finish renovations before moving in. But once I can at least pull most of the way into it, I’ll see what the actual clearance is once I reach the middle of the roof. When test fitting before purchase, I pulled the mag mount with the NMO2/70SH off the top.


That would make it easier to ignore garage issues. But we get some bad hailstorms around here from time to time, and the new place sits immediately on a main public road. With Super Duty trucks being so popular to steal, and tailgates being popular to steal, and being so easy to break into them for any opportunistic passers-by, I’d rather go ahead and pull the antenna off if it comes to that.

I'm going to highly suggest the super flexible Sti-Co. I stock a ton of them on my truck--it's a real problem solved. We get a lot of water delivery trucks that manage to break ANY other antenna while these keep going. Same thing for ambulances at one local hospital that shaves all the standard nmo quarter-waves off... Worth every penny. You'll never think of it again.
(Ignore the "replacement mast" portion, it's a standard NMO antenna)
 

KK6ZTE

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It'll flex a bit, but no damage or noticeable performance change. Being that they are flexible, they'll bend a bit (not like flat to the cab) at higher speeds (70-80).

I was running big heavy wideband 1/4 wave antennas with springs, the thick rod kind. I swapped them out for the StiCos on my service truck because I cover two counties and a lot of driving, the wind noise from the larger bases was too much. (2018 F-150)
 

Project25_MASTR

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They'll bend over to roughly a 45 degree max angle (normalized since it's a smooth arc typically). How much they bend over is also highly dependent on their length, placement and aerodynamic properties of the vehicle. For example, a 440 MHz 1/4 wave whip may be entirely in the turbulent flow (low pressure) caused by the windshield pushing air up and over the vehicle and as a result, may see little to no bending.
 
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