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Discussion Starter #1 (Edited)
Hello everyone! I’ve been a long time reader here but finally got around to my first real project with my XV.

I’ve taken my entire project and broken it into two separate forum posts since the people that may be interested in light bars may not necessarily care about ham radio antenna mounts. The link to my light bar installation is here:

http://www.subaruxvforum.com/forum/lighting-electrical/137393-slightly-over-engineered-light-bar-install.html

As someone that does a lot of camping and back-roads driving a, light bar has been on the list for a while. I’m also a licensed ham radio operator and have been contemplating adding a few NMO antenna mounts instead of messing around with magnet mounts that can scratch the paint on my roof.

Since both of these projects involve a significant amount of drilling, wiring, and dropping the headliner, I figured I’d combine the two and do some soundproofing as well.

Since the forums has plenty of how-to guides on sound proofing the XV, I’ll be skipping that piece altogether even though you’ll see some pieces show up in the photos.

Several parts of this project involved removing bolts that are safety-related and have factory torque specs for a reason. I highly encourage anyone trying to reproduce this same process go and spend the $34 USD to get the three-day Subaru Technical Information Service subscription. It really was a great resource to know where all of the odd clips were hiding and what torque specs to put fasteners back to after removing them:

https://techinfo.subaru.com/index.html

Similarly, a set of plastic interior removal tools (I used a Neiko 20598A set off of Amazon), a thorough metric (both standard and deep) socket set, and a sense of patience were invaluable in making this project work.

This Write-up:
1. Disassembly
2. NMO mount installation
3. Re-Assembly and Lessons Learned

1. Disassembly

This project involved a lot of prep work. Even before I started digging into this project, I started with cleaning my engine bay, getting a car wash and sweeping/washing the garage.



Next up was disconnecting the battery and setting it aside after opening all of the doors and rear hatch.





Getting started on removing the headliner, I folded all seats flat and started taking the plastic uppers out of the car. The Subaru SITs pdf “Upper Inner Trim” instruction does a better step by step than I can with my pictures, but got tricky when taking the A-pillar swivel-clips.

The entire yellow plastic part at the top of the A-pillar actually rotates 90 degrees before disengaging from the trim piece.



My fingers and needle nose pliers didn’t quite reach back far enough, but a pair of hemostats fit nicely



Much to my surprise, the overhead handles weren’t actually attached by fasteners, but rather overgrown push pin fasteners



Lights and visors came off without much hassle, and the B-pillar upper plastic was removed once the 17mm bolt was taken off for the seatbelt. *



*For the love of safety, please buy, borrow, or rent a real torque wrench to put these back when you’re done. On the 2015 Crosstrek XV Premium, bolt T2 has a torque spec of 30 Nm or 22.1 ft-lbs of torque. It’s not worth your life to put these back “tight enough”.

Once the plastic upper is out of the way, the weather stripping around all the doors comes off and the headliner starts to drop out of the way




It may be necessary to pull up part of the door sill panel to get the weather stripping out of the way. I just ended up removing all four and leaving them out of the way for most of this project.





Once the headliner starts dropping, it’s only the XM/FM antenna cables and the lighting/microphone cables that hold the piece in place. It took some bending and twisting with my wife to help get the liner out, but we did it without wrinkling the headliner. The trick is to make sure that anything that needs to get bent, is flexed towards the non-fabric side.


Now we’re ready to start drilling holes and adding pieces.



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3. NMO Permanent Antenna Mounts

For those that are either new to the hobby or just curious about ham radio, there are three general options when it comes to putting antennas on vehicles; 1. Magnetic mounts, 2. Edge clamp solutions, or 3. Through-hole mounting.

Magnetic mounts allow the flexibility to remove the antenna from the car, but can scratch and scuff the paint job on a roof or a trunk if you’re not careful to clean the location first of any dust or sand. There is the additional issue the base may be insulated from the rest of the vehicle body by paint and therefore be prevented from creating a good ground-plane.



Similarly, edge mounts that clamp onto a trunk or hood seam of a car can be quite sturdy and scratch through the paint to create a better ground plane, though most commercial mounts leave you with trying to route coaxial cable through a tight pinch space or use lossy thin coax to fish it nicely through existing vehicle gaps.



NMO mounts, originally developed by Motorola for use on vehicles get around these mounting issues by using a two piece back-stop and clamping nut setup that touches the metal skin they’re mounted on, providing a convenient means to use any kind of coax you’d like, and creating a strong mechanical connection that allows you to use longer 1/2 –wavelength antennas or survive the occasional garage door without concern.



Since for my light bar project, I already was going to have the entire headliner out I decided to put in a Larsen NMO-KHFUDFME and a Larsen NMO-KFME connector. If I had my choice again, I would have put in two of the KHFUDFME connectors since they’re designed to work with a wider range of antennas, have a nicer mounting body, and dual-shielded coax cable, but my local Ham Radio Outlet only had one of those in stock that particular day I dropped by.

Moving to the inside, since the light bar connector was going to be above the rear passenger door, I knew that I was going to be able to mount the antennas in the center of the roof



When separating any kind of transmitting/receiving antenna, the correct distance is “as far apart as possible”. After rolling your eyes at that answer, the slightly more specific value is 1/4 wavelength apart for whatever bands you’re running.

I built a spreadsheet that calculates the 1/4 wavelength separation in inches for the various bands I planned to be running as well as the bands the broadcast AM/FM radio receiver in the car would be sensitive to. Even though I wouldn’t be transmitting on the commercial frequencies, I wanted to make sure that both of my antennas wouldn’t be sitting exactly on that 1/4 wavelength distance away from the stock antenna and possibly inducing voltages on the antenna and potentially damaging the receiver.



If anyone would like a copy of this spreadsheet or recognizes an error I made, please PM me and I can send you a copy.


Measuring out that my antennas weren’t going to line themselves up on any particular harmonic, I marked where the two NMO mounts would go and made sure they were centered left to right on the car.



I missed taking a picture of the “before” NMO hole, but the process was identical to putting in my light bar power connector. The hole was marked on a piece of tape, center punched, center drilled, and then step drilled to a full 3/4 inch diameter before being deburred.





The long tail of coax was then fed through the hole



The locking nut and o-ring were both coated generously with Dow Corning #4 for waterproofing



A pair of pads were sanded down to bare metal where the NMO “feet” would be biting into the roof and wiped with Corrosion-X to make sure the connector base could form a good ground plane against the metal roof of the car



And finally the NMO nut was tightened on the top while being held in place from the bottom. It helped to hold the bottom piece with a 1/2 wrench to keep it from turning as the top nut was being compressed





On the inside, I just used a series of stick on adhesive pads and zip ties to hold the coax in place and prevent it from rattling around in the roof



This process was then repeated for the 2nd antenna mount located just a bit more forward.



I routed both pieces of coax down the drivers-side B-pillar and used plenty of tape and additional zip-tie blocks to keep the coax from rattling around in the pillar or rubbing against the seatbelt.



A short jaunt under the carpeting and the cables were pulled out through the pre-cut flaps that Subaru included underneath the driver’s seat



Up on top, a Larsen NMO-2/70 SH (short) antenna was installed on the nicer KHFUDFME mount and for the moment, a Tram hard plastic rain cap was put on the KFME mount.



A bit of cleanup from the metal shavings and Dow Corning #4 and this project was complete.

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3. Lessons Learned



This was definitely the most challenging and in-depth project to date that I’ve undertaken on any car I’ve owned. With a few months of researching and small-parts prep work, I was able to start and finish this by myself in about four days.

If I had to do it again, I would definitely invest in a better work light (or lights) for the garage and have some extra white body panel fasteners available since I definitely bent several of them while taking the paneling off. I would also order two of the KHFUDFME mounts rather than mixing the types.

In the future, I’ll probably add a GSM/LTE antenna to the empty NMO mount and use that as a permanent addition to my Wilson cell phone booster rather than relying on its magnetic antenna. As I explore deeper into the mountains, I may also consider moving up to a full 1/2 wavelength Larsen NMO-2/70 antenna rather than the 1/4 wavelength short one I have there today.

After several weeks of driving with the light bar and antenna, the only negative change to the car is a slight whistling noise from the bar between 30 and 55 mph. I’ve read about some people using door trim material to block some of the fins, but I am still playing with this solution.

I’m happy to answer questions and hopefully some of you can find this useful.

73!

KN0VNC
 

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Hey backpackingnerd, I don't know if it's just me or not, but I can't see a single one of your pictures. :thumb_smileyvault-e

Gerry
 

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Nice write up. Also can't see pictures here, though it might be me. What radio are you running? I've been considering a 857D for a while now.

73
N2MCB
 

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Discussion Starter #6
Hi Kirby,

For the moment I'm just running the antenna to a BaoFeng UV-5R, but I plan on putting in a Yaesu FT-8900R with the head unit off to the left of the steering column.

Photos should be fixed now.

Nice write up. Also can't see pictures here, though it might be me. What radio are you running? I've been considering a 857D for a while now.

73
N2MCB
 

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Hi backpackingnerd! Thanks, this is a great post.

I'm going to be installing a TM-D710 soon so this is really helpful.

Related question: Where the roof rails attach to the car, is there any opening into the car? I'd like to attach a light to the roof rail, run the power through the rail, and come out into the car. This would be convenient on the off chance that there is some sort of access hole between the roof and the rail. Any thoughts? I guess the other option is to run the power through a grommet in the roof, but, wow, that would seem to lead to long-term problems with water intrusion, corrosion, etc.
 

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While I am not planning on doing this project, it is none the less a great write-up and cool project to have done. Kudos !
 

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My goodness, I'm happy to hear there are other hams here! Thanks for the great write-up!

73
W5JNM
 

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Discussion Starter #10
Related question: Where the roof rails attach to the car, is there any opening into the car? I'd like to attach a light to the roof rail, run the power through the rail, and come out into the car. This would be convenient on the off chance that there is some sort of access hole between the roof and the rail. Any thoughts? I guess the other option is to run the power through a grommet in the roof, but, wow, that would seem to lead to long-term problems with water intrusion, corrosion, etc.

Hi Dug,

There aren't any convenient access holes from outside to inside the crosstrek (at least in my 2015). If you take a look at my light bar writeup I go through a bit of how I installed a sealed Amphenol cannon connector base to create a reusable connection from the bar to the interior (~1/2 way down):

https://www.subaruxvforum.com/forum/lighting-electrical/137393-slightly-over-engineered-light-bar-install.html
 

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That takes big you know what and commitment to that car forever to drill a hole in the roof.

You should be a technical writer, great job.
 

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Discussion Starter #13
That takes big you know what and commitment to that car forever to drill a hole in the roof.

You should be a technical writer, great job.
Thanks Goin2drt. In a former life I actually worked as a functional analyst doing requirements writing, guess it hasn't rubbed off yet.
 
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