Antenna Type for non-center-of-roof Installation (Third Brake Light, BackRack)

[chiwititsara]

I have a new '23 Super Duty F-250 and familiarity with drilling / installing NMO mounts in auto roofs. For now, however, I think I will start with a 'no-drill' mount like a Third-Brake-Light or Back Rack mount.

I am typically a fan of 1/4 wave antennas on NMO mounts in the center of the roof. I do not imagine the poor ground plane offered by the Brake Light or BackRack mounts will play well with 1/4 wave antennas.

Would I be better off using a 'no ground plane' 1/2 wave end fed antenna if I am using one of these non-ideal mounts? Primary frequencies will be amateur and commercial VHF.

I know mmckenna drilled his Super Duty but - with the amount of electronics on this vehicle and no service manual to understand the headliner removal procedure - I am hesitant to do this on a brand new truck.

 

[Cameron314]

I've used 1/2 waves on BackRacks in the past for a UHF system. For VHF that is about a 4 foot antenna so I think I'd just drill and do a 1/4 wave.

 

[mmckenna]

I know mmckenna drilled his Super Duty but - with the amount of electronics on this vehicle and no service manual to understand the headliner removal procedure - I am hesitant to do this on a brand new truck.

There is absolutely no reason to remove the headliner to install an antenna on these trucks. In fact, I'm having a hard time remembering the last time I've had to drop the headliner on any vehicle to install a permanent NMO.

I'd encourage just doing the center of the roof mount. Not just because it's my mantra, but because if you are going to put all the work into pulling in coaxial cable to the back of the cab for the 3rd brake light mount, you might as well just pull it to the center of the cab. Once and done.

Your truck, your choice. I don't judge.

You may have some challenges getting the antenna to tune well on the very edge of the ground plane like that, but it is not usually a big enough deal to worry about.
Either antenna is going to suffer from an impacted radiation pattern when installed at the very back edge of the roof like that.

I'd probably go with the half wave if that is your choice on location. Probably not a huge difference. Will depend on how far up the VHF band you plan on going. The 1/4 wave will give you more bandwidth compared to the 1/2 wave.

Those mounts get really expensive. I'd look at drilling just in front of the 3rd brake light as an option. You'll save money.

I've never had a headache rack mounted antenna work right. Ever. The lack of ground plane is going to really impact antenna performance.

 

[Project25_MASTR]

Simple answer is don't remove the headliner to install a NMO mount. It's a mount designed in a time period when vehicles had double walled roofs instead of a headliner.

Personally, I think the 3rd brake light mounts are extremely over priced...$300+ to accomplish something a $20 kit from Tessco can accomplish but in some applications (such as the Acari mounts) where vehicles are swapped through on a relatively short term it makes sense to have common used items mounted on a platform that can semi-easily transition between vehicles.

I'm even against the Breedlove mounts in most cases. Which is funny as I have one that I ordered simply because I removed a Panorama Sharkee from my pickup earlier this week only to discover when I had the roof repainted 7 years ago the body shop didn't fully paint under the mount so there is an area of just primer exposed with a standard NMO mount. So in my case a 3" diameter Breedlove mount is simply to cover the bare roof left by the shotty body work done that couldn't be inspected when I picked the vehicle up from the shop 7 years ago.

 

[chiwititsara]

There is absolutely no reason to remove the headliner to install an antenna on these trucks. In fact, I'm having a hard time remembering the last time I've had to drop the headliner on any vehicle to install a permanent NMO.

I'd encourage just doing the center of the roof mount. Not just because it's my mantra, but because if you are going to put all the work into pulling in coaxial cable to the back of the cab for the 3rd brake light mount, you might as well just pull it to the center of the cab. Once and done.

Your truck, your choice. I don't judge.

You may have some challenges getting the antenna to tune well on the very edge of the ground plane like that, but it is not usually a big enough deal to worry about.
Either antenna is going to suffer from an impacted radiation pattern when installed at the very back edge of the roof like that.

I'd probably go with the half wave if that is your choice on location. Probably not a huge difference. Will depend on how far up the VHF band you plan on going. The 1/4 wave will give you more bandwidth compared to the 1/2 wave.

Those mounts get really expensive. I'd look at drilling just in front of the 3rd brake light as an option. You'll save money.

I've never had a headache rack mounted antenna work right. Ever. The lack of ground plane is going to really impact antenna performance.

I ordered and received a BPD third brake light mount and have determined there is no way it is worth the money given the poor performance. I will be selling / returning and just using a Larsen metal plate if for some reason I do need to mount in that location.

mmckenna - very glad you joined this thread - I have zero issues drilling my roof but how would I center a mount without removing the headliner as you suggest? I have been searching YouTube for days and haven't found a single video even discussing a center-of-roof NMO mount on a current-gen Super Duty. I'd love to know how you did yours. My Lariat has no dome light in the middle of the headliner or anything point of access.

If the idea is to go from the outside, through the high mount rear brake light space, I have already removed the light assembly to look and unfortunately there is only about 3.5" of forward access before some serious sheet metal blocks the path forward. Were you suggesting there might be a way I could get an antenna forward of that space without dropping the headliner? Thanks in advance.

 

[mmckenna]

Easy way is to open one of the rear doors (on a crew cab) and pull the rubber gasket off around the top of the door opening towards the back of the cab.
That will expose the edge of the headliner.
That should be able to be -carefully- pulled down a few inches. You'll be able to look up and see the roof skin.

Here's how I did my 2018 F-350 crew cab:

From the rear edge of the cab where the sheet metal meets the third brake light, measure forward 24.5 inches. Lay down a couple of passes of 2" wide masking tape. Mark that spot.
Now, measure from the left/right edges of the roof and find the left/right center.
Measure everything again to make sure you've got it centered and 24.5" from the back edge of the sheet metal.

Drill your hole.

Vacuum up all the shavings carefully. Remove the masking tape. Have a cold drink.

Go inside the cab and remove the rear dome light over the rear seats. That takes some work, but it's doable.
Once you have that out of the way, you'll see a hole in the sheet metal above you. This gives you access to a front/rear running center rib.

From the topside, push the coaxial cable back towards the rear of the cab. When you think you are close, go back inside the cab and look for the coaxial cable through that hole. Might take you a few times, and fishing it out with a bent coat hanger, finger or other tool will allow you to pull the coax down into the cab.

Pull the coax through and go back up topside and install the NMO mount. Follow all the directions that come with it. Many mounts will come with a little tube of silicone grease to put on the O ring before you put it all together. Make sure you do that so the O ring will stay in place and won't bind up with tightening down the mount.

Go back inside the cab and make sure you have all the coax there coming out of the hole over the dome light. Don't leave any up there.

I took this chance to install a rubber grommet around the hole to protect the coax. I don't remember what size the hole was.

Route the coax laterally over to the side of the truck where you pulled the gasket out. Might take a few tries, but you'll get it.

If the truck has side curtain airbags, you want to be 100% sure you route the coax between the top of the airbag device and the roof of the truck.

I got all the slack coax pulled through.

I then routed it down the back corner of the cab. I pulled the trim off (I think you need a 7mm socket to remove one screw under a cover near the seat belt upper anchor point). Route the cable down behind the rear seat to the RF deck.

If you are mounting the radio up by the front seat, you want to do all this towards the front of the rear door, and route the cable down the B pillar to the floor and then to your radio.


Once you get this far, you'll see how easy the whole process is. Carefully reassemble everything and terminate your cable at the RF Deck/Radio.

Much cheaper than the center brake light mount, and will work much better. 24 inches in from the back of the cab and centered left/right will give you an ideal ground plane for VHF use.

Let me know if you need more help. I probably have some photos somewhere if you need to see it laid out.

 

[prcguy]

My experience is mostly from the 1970s and 80s but still works on new vehicles depending on air bag locations. Open a front or rear door that's closest to the front/rear location for the antenna. Grab and pull the rubber door seal down to about bottom of window height around the entire door area. This will expose the edge of the headliner. Gently pull down the edge of the headliner and using a flashlight determine if there are any obstructions for the proposed antenna spot.

I like to slide a length of thin hard plastic or sheet metal about 4ft long and a foot wide up into the area below the antenna spot between the metal roof and headliner to catch drill debris and to protect the headliner from the drill bit (for beginners). Locate the side to side center of roof by placing a bolt or similar on the roof and centering by eye based on lining up with the rear view mirror, brake light, etc. This can be slightly different that what is measured with a tape measure and can look more centered to the eye than a measurement. If the roof is ribbed then use the center of a rib or valley as center.

Drill the hole and start the end of the coax into the hole pointing towards the area where the door seal is removed. Sometimes I have to use a snake or tape the coax to an antenna whip to get the coax to the edge of the headliner, then run the coax down the side door pillar. Remove the foot trim around the bottom of the door and start routing the coax to wherever the radio will live under the carpet around the foot trim where you will find channels with other cables run from the factory. You can go under the back seat for a remote mount radio or just past the drivers feet area then angle under the drivers foot area to an underdash mount radio.

Reinstall the door pillar trim, rubber door seal and foot trim. Mount radio and run power cables, yada yada yada. I usually takes no more than 10 to 15 minutes from removing the door seal to having the hole drilled, mount installed and coax run. Unless you expose an air bag when lowering the headliner. In that case you have to carefully look forward or aft of the door opening for a safe coax run from the mount to a door or window pillar to run the coax down to the floor. You don't want the coax anywhere near where an air bag will deploy.

 

[Project25_MASTR]

Perhaps this will help in providing some images similar to what @mmckenna described as I just added two new mounts to the roof of my Sierra this weekend after 7 years of only running a single mount with a multi-band whip.

Weather stripping pulled out to gain visual access to the underside.

Drilled holes...all of the goodies on the roof were so I could mark and center between the support ribs in line with the existing antenna.

Both runs come out right there but go between the roof and airbag pack to not get into the way of side curtain deployment. I just work the weather strip back in as I move the coax down the (C in this case) pillar.

Installing to terminating (SMA connectors in this case) took me under an hour for both...and it's been almost 5 years since I've done a mobile install with any kind of regularity.

Somewhere I have a full length video of me doing it on my Jetta Sportwagen but I wasn't overly fond of the way it (the video) came out so I never put it up on Youtube.

 

[prcguy]

Years ago I worried about RF riding on the coax near air bags or their wiring causing an air bag to go off and a conversation with a good friend who was an engineer for Takata air bags says they will not trigger from high RF fields. If you want further piece of mind you can install three #43 ferrite mix or Laird 26 mix snap on ferrite beads at the antenna mount and also at the radio end to greatly reduce any stray VHF/UHF RF that might be riding on the coax.

 

[chiwititsara]

Go inside the cab and remove the rear dome light over the rear seats. That takes some work, but it's doable.
Once you have that out of the way, you'll see a hole in the sheet metal above you. This gives you access to a front/rear running center rib.

Once you get this far, you'll see how easy the whole process is. Carefully reassemble everything and terminate your cable at the RF Deck/Radio.

Much cheaper than the center brake light mount, and will work much better. 24 inches in from the back of the cab and centered left/right will give you an ideal ground plane for VHF use.

Let me know if you need more help. I probably have some photos somewhere if you need to see it laid out.

Amazing info here and from others. This is beyond helpful.

The biggest issue though continues to be that my Lariat Crew Cab (non-sunroof) has no central rear dome light. The only central overhead lighting is at the top of the front windshield, grouped with the sunglasses holder...which is odd because I thought 2017+ models were generally the same.

This has been my stumbling block all along...and why I thought I would need to drop the headliner. Will re-inspect for sanity as I digest these helpful posts.

 

[mmckenna]

Does this radio have a separate RF deck, or are you mounting it all up on the dash?

I think you can snake the coax all the way to the back of the cab. Try removing the center high mount stop light and see if you can see an access point behind there.

Unfortunately I've never had my hands on a Lariat, and the last F series I installed in was a 2018.

 

[chiwititsara]

I think you are onto something re access through the CHMSL. Picture here (not mine, but the same - have not looked any more deeply but this hole could go somewhere, ):


In past installs, I recall holding the lower portion of the mount in place as I initially threaded the upper ring. But (per prcguy's notes above) I guess that kind of access isn't necessary: I only need to push the coax-terminated bottom of the mount in from the top, thread on the upper ring, and fish the coax out from wherever it's dropped down into the roof cavity.

I had been planning to mount a FTM-3100R but if there is some significant advantage (aside from convenience) to not running coax all the way to the front dash, I also have a TYT quad-band (decent if not great Yaesu clone) with remote faceplate.

Lastly, my own 23 Lariat headliner image below for others' reference..

 

[ramal121]

As mmckenna mentioned there is a center channel that will trap your coax inside. There is, however, holes on the underside of this channel. You'd have to know where these are so you can drill your NMO somewhere close to make dropping the coax down to the headliner easier. You cannot get from this channel to the third brake light so forget about that.

Just ahead of the B pillar is a rib that goes side to side. In front of this rib there is no center channel and putting an antenna there is a lot easier but it will be forward of center. If you're good with the aesthetics, moving it there will not upset the pattern too bad ( at least compared to having it on the headache rack). An option.

If need be you can remove the visor, visor clip, and pop out the A pillar cover a little. This will allow better access by pulling down the headliner in that corner and let you look around. Easy enough to reassemble.

 

[mmckenna]

Just ahead of the B pillar is a rib that goes side to side. In front of this rib there is no center channel and putting an antenna there is a lot easier but it will be forward of center. If you're good with the aesthetics, moving it there will not upset the pattern too bad ( at least compared to having it on the headache rack). An option.

That's good to know, just in case I ever want to add another to my truck.

 

[mmckenna]

I think you are onto something re access through the CHMSL. Picture here (not mine, but the same - have not looked any more deeply but this hole could go somewhere, ):

Now that Ramal mentions it, it's bringing back memories. Yeah, not a route there. You'll need to get more creative.

Lastly, my own 23 Lariat headliner image below for others' reference..
View attachment 142369

Yep, different from my 2018 XL trim….

 

[chiwititsara]

As mmckenna mentioned there is a center channel that will trap your coax inside. There is, however, holes on the underside of this channel. You'd have to know where these are so you can drill your NMO somewhere close to make dropping the coax down to the headliner easier. You cannot get from this channel to the third brake light so forget about that.

Just ahead of the B pillar is a rib that goes side to side. In front of this rib there is no center channel and putting an antenna there is a lot easier but it will be forward of center. If you're good with the aesthetics, moving it there will not upset the pattern too bad ( at least compared to having it on the headache rack). An option.

If need be you can remove the visor, visor clip, and pop out the A pillar cover a little. This will allow better access by pulling down the headliner in that corner and let you look around. Easy enough to reassemble.

Given my aversion to the aesthetics of mounting a single antenna on the front half of the cab, could I not pull some headliner down from the rear or side rear door trim and rear of cab (rather than front of cab / visor clips)?

If I could take a peek at the rear center channel (which I assume is the extra dropped square portion of headliner centered above the rear seats in my picture above), I could drop the coax into that square area of extra headliner-roof clearance. Which I think is the 'center channel that will trap your coax' that you mention? That also has holes in it?



...once I found the (unterminated) coax in that center square area, I would use fish tape to pull it out to the side of the headliner and - without trying to take it forward past the large cross-rib dividing front to rear (which you note, and I can confirm is just ahead of the B pillar), drop it down the B pillar and along the floor trim up to the front of the dash.

In short, why not work from the rear or rear-sides of the headliner rather than front? (per my silly Microsoft Paint diagram).

And then follow mmckenna's advice to either drop the coax down the back of the cab or down the B pillar (which again, is in front of the offensive lateral cross bar)? Is there something particular difficult about starting to drop the headliner from the rear / sides rather than front visor clips?

It seems like the headliner has decent clearance behind it in most places described above (except for the lateral bar)...at least enough that a 0.195" diameter unterminated coax wire would slide around easily.

 

[mmckenna]

Years ago I purchased one of these. It's been very useful:

RIDGID CA-25 Micro Visual Inspection & Diagnostic Handheld Camera w/ 2.7 in. Color Display, 4 ft. Fixed Waterproof Camera Cable 40043 - The Home Depot

The RIDGID micro CA-25 features a 17 mm aluminum imager head with 4 ultra-bright LED lights, bringing superior image quality to its 2.7

www.homedepot.com

You can get similar tools from Harbor Freight. If you don't mind waiting, you can get less expensive ones that connect to your cell phone off Amazon.

 

[radioman2001]

Quote"
There is absolutely no reason to remove the headliner to install an antenna on these trucks. In fact, I'm having a hard time remembering the last time I've had to drop the headliner on any vehicle to install a permanent NMO.

Well then you havn't run into the new 2500HD crew cab by Chevy. There are EIGHT air bags in the head liner, and the roof panel is the thickness of an aluminum can. I just finished one and decided it was better to use an "L" bracket on the fender. Granted I am only installing either a VHF unity whip or a 800 mhz unity whip.

Did I say the metal was THIN, so thin you can't even use sheet metal crews they just strip out. Had to nut and bolt the radio under the seat, Gave up on a console that wasn't attached by the seat belt bolts.

 

[mmckenna]

Quote"
There is absolutely no reason to remove the headliner to install an antenna on these trucks. In fact, I'm having a hard time remembering the last time I've had to drop the headliner on any vehicle to install a permanent NMO.

Well then you havn't run into the new 2500HD crew cab by Chevy. There are EIGHT air bags in the head liner, and the roof panel is the thickness of an aluminum can. I just finished one and decided it was better to use an "L" bracket on the fender. Granted I am only installing either a VHF unity whip or a 800 mhz unity whip.

Did I say the metal was THIN, so thin you can't even use sheet metal crews they just strip out. Had to nut and bolt the radio under the seat, Gave up on a console that wasn't attached by the seat belt bolts.

I think the last GM truck I touched was a half ton 2020.
I've done many installs on aluminum body Fords, but haven't had that issue.

 

[radioman2001]

Yea it was a real pain, I did the install as a favor to the new Chief. What should have been at most a 3 hour install turned into 2 days.