3rd Brake Light Antenna Mounts

[Alec]

7 hours ago, dosw said:

This is how this thread has gone:

OP: Has anyone tried these?

Others: Those won't have a very good ground plane, and that will hamper your signal propagation.

OP: But this is what I want to do.

Others: *shrug* then why did you ask?

 

Exactly! 

I believe I only received 2 posts from people who have actually used that specific type of mounting device and provided some feedback about them.  Nobody actually addressed my original questions, which were "Does it leak?" and "Are they strong?". 

The other posts that provided alternative mounting solutions, alternate recommendations or general antenna considerations regarding ground plane etc. were all valuable answers or comments to different questions that I did not specifically ask.  I am still appreciative and thanked those people for their contributions to the topic.  Looking at my OP I did not ask "what is the best way to mount an antenna?" 

Sorry if my communications sounded dismissive of others effort to help as that was not my intention.

[tcp2525]

4 hours ago, Alec said:

@WSEZ864 Thanks for the suggestion about the back rack, and for the photo!  Very helpful.  That is certainly an interesting option worthy of consideration. 

@WRUU653 Thanks for the A-Pillar suggestion.  I do understand compromises... 

Cost isn't a primary consideration for me, but even so the 3rd tail-light mount is in itself sort of a compromise, rather than following the recommendation of the "drill-baby-drill" enthusiasts who advocate for just installing that NMO mount.  While an NMO mount installed dead center of the roof of my truck cab might be the best solution for RF purposes, that isn't necessarily the best solution for my purposes.

I

@WRUE951

 

Putting your antenna dead center of the roof for that "perfect" ground plane is overrated and only matters to people that want to sound like they are smart. Sure, there's going to be lobes were you have a strong signal and others where it is going to be weak. Guess what? It doesn't really matter because you're not driving in a straight line +/- 1° 100% of the time. So your radiation pattern is always changing just as long as you are moving. I can understand your apprehension to drill, that's fine. You can use whatever mount you want and put it in a spot that's easy and convenient for you and your performance will be good.

I put my 2m/70cm NMO antenna right above the 3rd brake light and it performs really well. Very easy install and didn't have to pull the headliner down. The Midland for GMRS NMO is close to center, not perfect and performance is good. Don't sweat it, enjoy it.

[WRUE951]

2 hours ago, tcp2525 said:

Putting your antenna dead center of the roof for that "perfect" ground plane is overrated and only matters to people that want to sound like they are smart. Sure, there's going to be lobes were you have a strong signal and others where it is going to be weak. Guess what? It doesn't really matter because you're not driving in a straight line +/- 1° 100% of the time. So your radiation pattern is always changing just as long as you are moving. I can understand your apprehension to drill, that's fine. You can use whatever mount you want and put it in a spot that's easy and convenient for you and your performance will be good.

I put my 2m/70cm NMO antenna right above the 3rd brake light and it performs really well. Very easy install and didn't have to pull the headliner down. The Midland for GMRS NMO is close to center, not perfect and performance is good. Don't sweat it, enjoy it.

for 70cm i think all you need for a perfect ground plane is something in neighborhood of 6-8 inches and yes ground plane does  help in radiation  pattern for long distances .   https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/

[tcp2525]

6 hours ago, WRUE951 said:

for 70cm i think all you need for a perfect ground plane is something in neighborhood of 6-8 inches and yes ground plane does  help in radiation  pattern for long distances .   https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/

Yep, only proves my point. Way too much overemphasis on seeking the "perfect" ground plane when most people accidentally get it right without thinking about it.

[WRYZ926]

The metal underneath your antenna doesn't even need to be a solid. I run my Comet 2x4SR on a magnet mount stuck to the expanded metal cargo rack on the back of my Honda Pioneer 500. And it works well on 2m, 70cm, MURS, and GMRS.

 

And @WRUE951 is correct, you only need 6 inches of metal all the way around an antenna for 70cm and GMRS. You will want  18 inches all the way around for 2m and MURS. But a good ground plane all the way around your antenna is not 100% needed. Yes the antenna will be a bit directional without a full ground plane but it will still work

Yes a no ground plane antenna will work better when you don't have good ground plane but they will benefit from having one.

[SteveShannon]

 This picture, which I believe originated from Laird, shows how much or how little placing an antenna base off center, or even at the corner of the roof actually makes: 0.02 dB less when moved to a corner of the roof.  I don’t believe any of us would even notice that. Moving it from the roof makes more difference of course.

[WRUE951]

1 hour ago, SteveShannon said:

 This picture, which I believe originated from Laird, shows how much or how little placing an antenna base off center, or even at the corner of the roof actually makes: 0.02 dB less when moved to a corner of the roof.  I don’t believe any of us would even notice that. Moving it from the roof makes more difference of course.

I like the 'Bullseye'  mark.  

[wayoverthere]

On 4/16/2025 at 6:20 AM, SteveShannon said:

 This picture, which I believe originated from Laird, shows how much or how little placing an antenna base off center, or even at the corner of the roof actually makes: 0.02 dB less when moved to a corner of the roof.  I don’t believe any of us would even notice that. Moving it from the roof makes more difference of course.

You know, having seen that graphic many times, I just noticed a couple things I hadn't before. First, there's no rating for a hood lip or fender mount, just a mag mount. Second, the permanent trunk mount is actually rated more loss (-2.8db) compared to a mag mount on the trunk (-2.1db).

[WRUE951]

1 hour ago, wayoverthere said:

You know, having seen that graphic many times, I just noticed a couple things I hadn't before. First, there's no rating for a hood lip or fender mount, just a mag mount. Second, the permanent trunk mount is actually rated more loss (-2.8db) compared to a mag mount on the trunk (-2.1db).

When i had my JK Jeep,  my Midland SMRS antenna was mounted on the left cowl back side of the hood.  It worked fantastic in any direction.  Now with my 10 meter mounted there, not so good.  In fact i couldn't find a single place to mount my 10 Meter that worked as will as it does on my truck.  

[tcp2525]

3 hours ago, wayoverthere said:

You know, having seen that graphic many times, I just noticed a couple things I hadn't before. First, there's no rating for a hood lip or fender mount, just a mag mount. Second, the permanent trunk mount is actually rated more loss (-2.8db) compared to a mag mount on the trunk (-2.1db).

One should keep in mind with that pic on whether or not the vehicle would be moving in any random direction as we all do when traveling. What frequency? Too many variable to take it with even a half grain of salt. You could have -2.8db and a split second later you would have +2.8db to the receiving station.. Now if the car was stationary in an anechoic chamber there's a better chance of those numbers be acceptable. But when we get back to the real world you wouldn't be able to tell where the antenna is placed on the car.

[wayoverthere]

14 hours ago, tcp2525 said:

One should keep in mind with that pic on whether or not the vehicle would be moving in any random direction as we all do when traveling. What frequency? Too many variable to take it with even a half grain of salt. You could have -2.8db and a split second later you would have +2.8db to the receiving station.. Now if the car was stationary in an anechoic chamber there's a better chance of those numbers be acceptable. But when we get back to the real world you wouldn't be able to tell where the antenna is placed on the car.

Yeah, with the shape of the ground plane of the trunk (dependent on vehicle and frequency), I'd expect some directionality, given most will have more ground plane to the sides than front to back. id also expect the greenhouse to be blocking/shading the signal in some directions too.

It just struck me as a little odd that permanent mounting in that location would mean more loss than a mag mount in the same place, where on the roof it's the other way around.

[WRCR724]

@Alec Do you mainly use your radio to talk on repeaters or simplex? If you're in an area where there's good repeater coverage, and that's what you mainly use, whatever compromise you make with antenna location should be negligible. 

Let us know what you end up doing and share some pictures. 

[SteveShannon]

42 minutes ago, wayoverthere said:

Yeah, with the shape of the ground plane of the trunk (dependent on vehicle and frequency), I'd expect some directionality, given most will have more ground plane to the sides than front to back. id also expect the greenhouse to be blocking/shading the signal in some directions too.

It just struck me as a little odd that permanent mounting in that location would mean more loss than a mag mount in the same place, where on the roof it's the other way around.

I’m not certain that surplus ground plane in one direction more than another affects directionality, much if any. I absolutely agree that some antennas require a minimum radius ground plane and I suspect that having that at least the minimum radius ground plane in all directions contributes to more even 360° coverage, but for GMRS that radius is relatively small. 
I’m old enough to remember how CB signals were pictured as very off center when an antenna was mounted at one edge of a vehicle, but the ground plane minimum radius is much larger for CB than for GMRS. 

[Alec]

1 hour ago, WRCR724 said:

Do you mainly use your radio to talk on repeaters or simplex? If you're in an area where there's good repeater coverage, and that's what you mainly use, whatever compromise you make with antenna location should be negligible. 

Let us know what you end up doing and share some pictures. 

Thanks for that input! 

For occasional 2m/70cm I use a very good local linked repeater network without any problems.   For GMRS, I use mostly short distance simplex when travelling with a group or at the lake or other destination.  The performance from my current mag mount which I usually place on the cab directly in front of the 3rd taillight, (basically where the antenna would be if I use one of these 3rd taillight mounts) works just fine!    I like that location (up and centered) because it keeps the antenna up and out of the way of getting things in/out of the truck bed and I don't have to stare at it while driving.    All the discussion about the effectiveness of the ground plane, while interesting, and not at all irrelevant, is just not too significant of a factor for my purposes.  That's why my OP was a question more about the antenna mount itself (water leaks, strength etc.) and less about the RF propagation characteristics associated with its location which seems to be the direction the thread drifted.   I'm not going to drill into my roof and I'm sort of tired of taking the mag mount on and off, so without any specific feedback that indicates that this type of mount is structurally problematic to my vehicle, l will probably give one of these mounts a try and hope for the best.

[Alec]

On 4/15/2025 at 5:30 PM, tcp2525 said:

Putting your antenna dead center of the roof for that "perfect" ground plane is overrated...

Don't sweat it, enjoy it.

Good advice.  Thanks for that!

[tcp2525]

2 hours ago, wayoverthere said:

Yeah, with the shape of the ground plane of the trunk (dependent on vehicle and frequency), I'd expect some directionality, given most will have more ground plane to the sides than front to back. id also expect the greenhouse to be blocking/shading the signal in some directions too.

It just struck me as a little odd that permanent mounting in that location would mean more loss than a mag mount in the same place, where on the roof it's the other way around.

For a real world comparison, a roof mounted antenna on my F150 vs trunk lip mount on the hood of my Lincoln (Glass Roof) yielded the same performance measured by my trusty Seat-O-Pants meter driving the same long distance route. I reluctantly fought the idea of mounting it on the corner of the hood since it is such a crappy location. Both antennas were Larsen NMO 2/70B. I was surprised by the REAL WORLD performance.

[WSBT754]

I purchased one of the Larsen Electronics 3rd brake light mounts for my 2016 F-150. I do have a NMO mount in the center of the roof that held a quarter wave Browning CB antenna, that sucker whistled terribly probably from accidentally placing it in the exact spot where the air comes over the roof and hit the antenna.

I now use the NMO mount for a dual band antenna and moved the CB antenna to the brake light mount.

The most important part of installing it is to evenly tighten the screws on the mount to spread the pressure evenly on the gasket. Thus far, in the spring rain season of Michigan I have not had any leaks coming in through the mount. It is a very rigid mount and I have not had any concerns as yet about holding up to the daily drive and/or vibrations.

As to the headliner, at least on my Ford it was very easy to run the coax. I just reached up behind the headliner and grabbed the coax connector and pulled it into the truck until all the slack was gone. Then just pushed it back up into the headliner area as I worked my way over to the side and was able to get it behind the trim piece until it was all the way to the floor. Popped off the bottom moulding and ran it over to where the front passenger seat is and fed it under the carpet to a seat mound hole in the carpet and to my radio. Pretty easy install, at least on my truck.

[Alec]

4 hours ago, WSBT754 said:

I purchased one of the Larsen Electronics 3rd brake light mounts for my 2016 F-150.

The most important part of installing it is to evenly tighten the screws on the mount to spread the pressure evenly on the gasket. Thus far, in the spring rain season of Michigan I have not had any leaks coming in through the mount. It is a very rigid mount and I have not had any concerns as yet about holding up to the daily drive and/or vibrations.

Pretty easy install, at least on my truck.

Great information...  Glad to hear that it is working well for you.  THANKS!

[tcp2525]

8 hours ago, WSBT754 said:

I purchased one of the Larsen Electronics 3rd brake light mounts for my 2016 F-150. I do have a NMO mount in the center of the roof that held a quarter wave Browning CB antenna, that sucker whistled terribly probably from accidentally placing it in the exact spot where the air comes over the roof and hit the antenna.

I now use the NMO mount for a dual band antenna and moved the CB antenna to the brake light mount.

The most important part of installing it is to evenly tighten the screws on the mount to spread the pressure evenly on the gasket. Thus far, in the spring rain season of Michigan I have not had any leaks coming in through the mount. It is a very rigid mount and I have not had any concerns as yet about holding up to the daily drive and/or vibrations.

As to the headliner, at least on my Ford it was very easy to run the coax. I just reached up behind the headliner and grabbed the coax connector and pulled it into the truck until all the slack was gone. Then just pushed it back up into the headliner area as I worked my way over to the side and was able to get it behind the trim piece until it was all the way to the floor. Popped off the bottom moulding and ran it over to where the front passenger seat is and fed it under the carpet to a seat mound hole in the carpet and to my radio. Pretty easy install, at least on my truck.

Nice! the F150 is by far the easiest truck to install gear in. Lots of room and many spots to install radios, which is only limited by your imagination. Keeping it covert. And you won't find my GMRS radio.