Another antenna question

k9medic

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#1
I am currently running an Mfj-1402 dual band antenna on what amounts to a homemade hood Mount for an nmo attachment.

SWR’s are less than 2:1 and everything ohms to Zero.

Recently I have though about drilling to Nmo mounts into the roof and separating the antennas into a single 1/4 wave vhf antennas and a stubby/ covert uhf antenna.

Here is my main question before I dig into this - will really see an improvement if I do this?




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#2
Yes, it would be worth it.

The rusting bracket should be one indication.

Putting the antenna on a proper ground plane will help performance. That means putting it center of the cab. You can easily do that with a 1/4 wave VHF and a 1/4 wave UHF antenna. The equal ground plane in all directions will make it truly omni-direction. As you have your antenna installed right now, the radiation pattern is lopsided.

NMO's, if installed correctly, will not leak and will likely outlast the rest of the truck. It doesn't impact trade in value.

A 1/4 wave antenna is also very broad banded, much more than the high gain antennas. This can be useful if you are operating across wide chunks of spectrum on UHF. If you are using commercial gear and are licensed to operate outside the amateur bands, it really helps since the wider bandwidth antennas give you lower SWR across the bands.

Not sure where you are located, but 1/4 wave antennas also have a more favorable radiation pattern if you are in the mountains.

I've installed a lot of NMO mounts over the last (almost) 30 years. All my personal vehicles have them, so do my work vehicles. I've never regretted doing the full install.

Plus, it just looks w-a-y better. Lower profile, more professional, more durable.
 
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#3
I should add, after rereading your post…

The low profile UHF antennas are fine, but a UHF quarter wave will work better. It's only 6 inches tall, and probably lower profile than the puck style antennas.

Also, on your current install, not sure what frequencies you are running, but getting below 2.0:1 SWR shouldn't be an issue. I've swept my antennas with my work analyzer as well as a Bird 43, and getting it down to 1.2:1 across the amateur bands is easy. I've got something like 1.6:1 across the 144-170MHz band on my VHF quarter wave.
 

k9medic

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#4
I'm in Florida so thankfully no mountains. The only reason why I mention the covert UHF antenna is because I already have one.
 
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#5
Drilled NMO roof mounts are the professional way to go. Just be careful... working with interiors in today's vehicles can be a PITA, removing the headliner can be very tedious. Be aware of any airbag locations such as side airbags. My advice would be to get professional help.
 
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#6
Drilled NMO roof mounts are the professional way to go. Just be careful... working with interiors in today's vehicles can be a PITA, removing the headliner can be very tedious. Be aware of any airbag locations such as side airbags. My advice would be to get professional help.


The side curtain airbags made this more of a PITA than it’s worth. They can be anywhere from the A post to the edge above the window to the B post. I wouldn’t want to pull down a headliner in any kind of newer vehicle. Agree with the above. External mounts, no problem, but I’m not interested in drilling holes through the roof for small gains.
 

k9medic

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#7
The side curtain airbags made this more of a PITA than it’s worth. They can be anywhere from the A post to the edge above the window to the B post. I wouldn’t want to pull down a headliner in any kind of newer vehicle. Agree with the above. External mounts, no problem, but I’m not interested in drilling holes through the roof for small gains.


This is kind of where I am at now.

If I would see a decent change then I have no problem doing so but for a little bit of an increase is it worth it?


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#8
This is kind of where I am at now.

If I would see a decent change then I have no problem doing so but for a little bit of an increase is it worth it?
What model/year truck is it?
There's a lot of people that have done installs as part of their job that may be able to give you insight.

I've installed a lot of NMO mounts in vehicles with side curtain airbags, and it's not difficult and it does not require dropping the headliner.

The "worth" depends on the individual. If this is a scanner/hobby/amateur radio, then probably not. Slap a mag mount on there and be on your way. If it's a work radio where you need it to work well, then it's absolutely worth it. As I've said before, there's a really good reason public safety installs are done this way. If someones life or your own depends on your radio, then ask yourself if it's worth cutting corners on the install?
 
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#9
This is kind of where I am at now.

If I would see a decent change then I have no problem doing so but for a little bit of an increase is it worth it?


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YES. Yes it is worth it. You will see improved coverage. The antennas will also not be directional as they are with an ‘L’ bracket on a compromised ground plane.

They also look a lot nicer drilled.


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k9medic

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#11
Well I went ahead and drilled two new NMO mounts. I figure it's easier to ask for forgiveness.

Time will tell if I it improves tx/rx.
 

k9medic

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#13
I used a three-quarter inch step drill bit to drill the hole after drilling a small pilot hole.

Everything else was plug and play intuitive And I did not have to drop the headliner.

I might add that my vehicle is not a off the lot vehicle so it may have been easier for me.


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#14
The short mfj is likely a decent antenna as low profile antennas go but since it is a 1\4 wave design on 2 meters it requires a excellent ground plane to work which you don't have with that mounting location.
.......
If it is a true 1\2 wave on 440, it would work better than a 1\4 wave in that location for certain but it would still be compromised.
.....
I use nothing but 1\2 wave UHF antennas on every police, fire, or business mobile due to the superior pattern and their abilty to perform well even with compromised ground planes.
.....
Where clearance allows i install 1\2 wave vhf antennas as well.
........
Most two way shops use ground plane dependant antennas on trunks, hoods, and light bars which results in poor performance.
......
I've replaced hundreds of 1\4 waves, 5\8 waves, and colinear antennas over the decades incorrectly installed in those areas.
 

AI7PM

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#15
Everything mckenna said and more.

BTW, the side curtain airbag issue is not what people make it out to be. Run your coax BEHIND everything else you find, and you'll be fine. Ignore the naysayers, as there's plenty of pro advisers in here to help you.

It would drive me nuts to do anything but a proper NMO install.
 
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#16
Everything mckenna said and more.

BTW, the side curtain airbag issue is not what people make it out to be. Run your coax BEHIND everything else you find, and you'll be fine. Ignore the naysayers, as there's plenty of pro advisers in here to help you.

It would drive me nuts to do anything but a proper NMO install.
Most people also don't understand how the curtains deploy. Key thing is just to not run the coax through the deployment zone (never put the coax between the bag and headliner) and instead run it behind (between bag and roof) anytime you have to transition to a pillar.
 
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#17
Not knowing if the OP had ever installed a drilled NMO or the age of his vehicle, I will stand by my comments in post #5.

Drilled NMO is the pro way to go but there are pitfalls to be aware of... therefore my suggestion to seek professional advice before attempting this task.

There is a big difference between working on a 25 yr old beater and a new 2018 whatever. This applies to not just antenna work but all areas of radio installation. With things like CANBUS and ESS and, yes, SRS, you had better know what you what you are doing before making modifications.

Fortunately it sounds like all went well for the OP and hopefully he enjoys improved TX/RX.
 
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#18
I used a three-quarter inch step drill bit to drill the hole after drilling a small pilot hole.
Everything else was plug and play intuitive And I did not have to drop the headliner.
I might add that my vehicle is not a off the lot vehicle so it may have been easier for me.
And this guy did NOT even have or use the correct tool. And it worked out good.
 

k9medic

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#19
Correct. I used a step drill bit which worked just fine.

Last time I dropped an NMO Mount in a roof it was 1999.

Vehicle is an issued 2014 Tahoe so I had plenty of room to work with.


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#20
Vehicle is an issued 2014 Tahoe so I had plenty of room to work with.
Well, there ya' go.
I've installed a lot of NMO's on that series pickup. Been a while since I've done a Tahoe, but since those are pretty close to the pickups, and, they use the Tahoes as police vehicles, it's a simple task. The large American vehicles are really easy to install in, as you've discovered.

A full size vehicle will really give you a nice big ground plane to work with. I'd suggest stepping up from the MFJ antenna to something a bit more 'commercial'. If you are just running VHF, get a 1/4 wave VHF whip. If you are running dual band, something like a Larsen NMO-2/70 or NMO-2/70SH would be a good option.
 
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