How I Installed a Ham Radio Antenna on my Jeep Wrangler TJ (VHF/UHF)
The End Result
I wanted to mount an amateur radio antenna on my Wrangler that was more permanent than the magnetic mount I already had on the hood (partly because mag mounts damage the paint), but I had a few specific design requirements for the project.
- Effective dual-band use of 2m/70cm bands, including ground plane considerations. This means I can't put it on the roof (no ground plane) or on the bumper (see propagation diagrams below)
- Semi-permanent install: no need to set up anything when I want to use the radio
- Clean install: no cables cluttering the interior area of the Jeep
- Little-to-no permanent modification to the vehicle
Just like in my Truck Antenna Install, I started by recognizing that every antenna is a compromise and this is no exception...so I looked for the best equipment to fit the criteria above. I settled on the Nagoya NMO-72 19.25" NMO Mount Dual Band Antenna (145/440Mhz) just like the truck install, but I didn't need a multi-axis mount so I got the Tram 1246B NMO Trunk Lip Mount and put it on the hood.
Why did I put it on the hood? I thought you'd never ask. Here are the general guidelines that I'll come back to after a short explanation of mounting antennas on vehicles more generally. (The roof is the best place but that doesn't work for Wranglers.)
- Mount the antenna above the body tub. This helps to avoid vertical metal surfaces, like the tailgate (license plate mount), body panels (bumper mount), and spare tire. Technically even the roll cage affects propagation, but not by much so that's a compromise I'll accept.
- Maximize the horizontal ground plane. On a Wrangler, a hood is really the only large horizontal surface usable as a ground plane.
- Separate antennas by at least 18". Don't put your ham radio antenna next to the FM radio antenna.
- Consider SWR--putting an antenna between the tailgate and spare tire is a terrible idea. It might sound like it works, but it might be damaging your radio.
- Protect the antenna so it's less likely to be torn off by trail obstacles.
If you don't want to read the background, jump right to the Install Instructions
Because honest penny is better than a crooked dollar, I want to tell you that some links below--like the Amazon ones--are affiliate links, meaning I'll get a few cents if you buy something from there. It doesn't change your costs at all because it comes from advertizing budgets, and it helps pay hosting costs for the page.
| Products Used for This Install |
Here are the basic products I used for this install. Aside from the antenna and mount, the
rain cap is used to protect the mount's electrical connections in case you need to remove the antenna for some reason and the SMA-to-SO-239 adapter is only used to connect this antenna to a Baofeng UV-5R platform radio (or any other radio with an SMA-male connection on the radio). You can also get a right-angle version if it fits your setup better.
| Why Mount the Antenna on the Roof? |
Check out the propagation image to the left, illustrating the impact antenna mounting location has on how the signal travels. Note that when you mount your antenna, you may not notice a difference on receive, and it will be difficult for you to detect the difference between each mounting location when you're the one transmitting...but transmissions are where mounting location has the most impact.
There are three primary reasons why mounting location affects signal propagation.
ONE. The main reason driving the difference between the first two examples is ground plane. When an antenna is mounted on the trunk, as in the first example, the antenna has a stronger grounding surface toward the front the vehicle than the small surface toward the back. As long as nothing on the vehicle blocks the signal toward the front, the signal will propagate stronger in that direction.
Mounting the antenna in the center of the roof, which is the best location for signal propagation, offers a ground plane that's balanced in all directions. Does this matter? That answer depends on your use-case. If you primarily use your radio to get traffic reports from in front you on a straight road like an interstate, you may not care much what the propagation pattern looks like behind you. But if you're the lead Jeep on a mountain road and need to communicate with the tail end of the formation, the propagation toward the rear will limit the distance at which you can communicate.
Additionally, mounting the antenna on the roof offers a height advantage, making it less likely that other vehicles can interfere with your signal. That is not illustrated on this propagation chart.
"...the center of an automobile roof is considered the best for mobile antenna placement, followed by the center of the trunk lid, the fenders, and then on-glass mounting. This ranking is determined by the amount of ground plane provided by the positioning, and clearance from obstruction (i.e.: the roof line), and is the reason the center of the roof is considered the ideal mounting location, provided the roof is metal."
Source: Larsen Antennas, Amateur Antenna Products, vol 2, pp.17.
Click for Larger Image
TWO. The second reason, which generally has less of an impact than ground plane considerations, is whether parts of the vehicle will block the transmissions in any direction. (This is the main reason we want an external antenna in the first place--sitting inside the vehicle basically means you're in an electrically-shielded box, so transmitting with a handheld means a lot of the signals will bounce around inside the vehicle.)
But this applies a little differently for Wrangler owners than for other vehicles. First, our roofs are not metal. Assuming we can get a good antenna orientation (without hitting the NA-771 on the ceiling, for example) the roof will not block our signals. Second, we often have roof racks or other equipment that might interfere with effective transmission. If your antenna is mounted to the roof rack, and it's behind the spare tire or Pelican case full of metal tools up there, you will experience degraded performance.
THREE. This brings us to the third reason, which isn't illustrated in that image but directly affects many Wrangler owners. Jeepers often mount antennas to the spare tire carrier because it's so convenient...but that's a TERRIBLE location! Not only does it lack a ground plane almost entirely (unless you design one into the mount), but much of the antenna itself is between the metal tailgate and metal wheel. This has two major impacts. First, not as much of your signal escapes that shielding, so your signal won't travel as far at a given power. Second, and most importantly, all that metal is reflecting the signal back into your antenna and sending it back toward your radio! If you measure the standing wave ratio (SWR) of an antenna mounted on the hood/roof/trunk with one mounted on the spare tire carrier, you're likely to find a dangerously high SWR, cause your radio to decrease power if it has a self-protect mode, or degrade performance in other ways.
(I use the cheap and tiny Surecom SW-33 Mk II SWR Meter and directional watt meter for these measurements.)
Often, people with bad mounting locations will compensate by turning their radio volume up and just dealing with the static. (Here, for example.) Then when someone transmits with a properly mounted radio, their clear signal comes blasting through louder than the other operators and people think they're the problem.
"The illuminated areas [to the left] represent actual intensity and azimuth measurements made at the testing facilities of Hy-Gain Electronics. The antenna used was a full-length 108-inch whip tuned to 27.065 MHz. The roof-top mount is the best position for all-round radiation, the left rear bumper just about the worst - except in its favored direction where the lobe is substantially stronger. When the car is in motion and turning, you can see why there are extreme variations in signal strength."
Source: Ruyle, Robert L. (W0FCH, KGI-3471). "A Blindfolded Choice is No Choice at All," Popular Electronics, November 1966. Citation and image from RF Cafe.
Click for Larger Image
| So How Does This Apply to Wranglers? |
So how to those basics apply to Wranglers? Basically, we can't put an antenna on roof (unless we add a ground plane somehow), and we probably don't want to anyway because a branch could rip it off. But some other principles apply. Here are some general guidelines:
- Mount the antenna above the body tub. This helps to avoid vertical metal surfaces, like the tailgate (license plate mount), body panels (bumper mount), and spare tire. Technically even the roll cage affects propagation, but not by much so that's a compromise I'll accept.
- Maximize the horizontal ground plane. On a Wrangler, a hood is really the only large horizontal surface usable as a ground plane.
- Separate antennas by at least 18". Don't put your ham radio antenna next to the FM radio antenna.
- Consider SWR--putting an antenna between the tailgate and spare tire is a terrible idea. It might sound like it works, but it might be damaging your radio.
- Protect the antenna so it's less likely to be torn off by trail obstacles.
For these reasons, I decided the hood cowling was the best place to mount the antenna. It requires very little permanent alteration and provides a good balance of performance, ease of install, and reversability if I decide to remove it.
I couldn't put it in the center of the cowling because the eye screws on the mount need more space than the little pieces inside the vents. Then I chose the passenger side to keep it farther out of the driver's view. This puts it a little closer to the FM stereo's antenna, but it'll do.
| Installing the Tram Lip Mount and Nagoya NMO-72 Dual Band Antenna onto a Jeep Wrangler TJ Hood Cowl |
Here are some more close-ups so you can see the end result.
Step-by-Step Instructions
First, mount the antenna onto the cowl.
- Take the hood cowl off the Jeep. This means removing the wipers and unscrewing the cowl. (While you're at it, clean out all the debris in the drain so you don't get water inside the cab when it rains.) Here's a good video showing this process.
- Dremel the screen. The goal is to slide the mount's lip over the edge of the cowl's vent hole. Look at the underside of the cowling and you'll see the screen that prevents (most) debris from entering the cavity. Using a Dremel with a cutoff wheel or other relatively precise tool, trim away only the lines of the screen you need to peel back the screen far enough to slide the antenna mount's lip through the vent hole.
- Slide the coax cable through the vent hole and the hole you just created in the screen.
- Mount the lip onto the cowl and tighten the eye screws.
Second, run the coax through the firewall. TJs have an existing hole in the firewall, plugged by a grommet, right above the gas pedal. See the pic below for reference and a close-up.
- Inside the cavity below the cowl, I was able to pull the plastic liner back far enough to pull the coax through the gap and into the engine compartment. You can reinstall the cowl at this time, and leave the coax coiled on the motor while you drill the grommet.
- Drill the grommet. Find the grommet in the pic below. Drill a whole big enough to fit whatever kind of fitting you ordered for your antenna. I used a UHF connector so I drilled kind of a big hole. (A better answer would be to buy a crimper and drill a hole exactly the size of the coax, run it through, and then crimp on a new fitting...but I don't have a crimper so I just bought the antenna kit with a UHF fitting already attached and drilled the hole bigger.)
Entering Cab (Reference)
Entering Cab (close-up)
- Run the coax through the grommet and through the firewall into the cab. Replace the grommet into the hole in the firewall.
- Use heat resistant tape to affix the coax to the firewall. This step is probably optional, but it made me feel better. First, it kept the coax in place. Second, it covered the hole I drilled in the grommet to keep water out. Third, the aluminum offers some measure of heat protection to the coax. Fourth, the aluminum probably offers some measure of protection from electronic interference generate by the motor. It might help if you wash the dirt off the firewall before trying to stick the tape to it.
The image below is kind of hard to make out, but it shows the path of the coax and heat resistant tape from the cowl (top of image) to the grommet, which is covered by the silver tape near the middle of the image.
From Cowl to Engine Compartment
Third, run the coax around the cab until you get it to your radio mounting location.
- The best option would be to trim the coax to length and crimp on your connector, if you have the tools. I do not.
- That means I have some extra coax length to account for. I put mine the under the floor mat. But the key here is DO NOT COIL THE COAX! Coiling the coax can create inductance when you transmit, which causes system problems, so just either run it in a serpentine pattern instead of coiling it.
- Connect to radio. You're done.
| Also See How I Mounted the Baofeng BF-F8 in the Wrangler! |
On the trail, I often use the UV-5R platform radios because they work, they're cheap, and it doesn't matter much if one breaks or I drop it in the river. I keep at least two in each vehicle as part of my EMCOMM kits, so it made sense to find a way to mount it inside the Jeep.
Kinda need a hand mic to use it this way, which is much more convenient if you have an externally-mounted antenna so you don't have to fiddle with the cable when you talk on the radio. It's not entirely necessary, but it helps. I use the Code Red Signal 21-K.
Check out the Mounting Instructions Here!
Please email me with any questions about this project and I'll try to answer them!
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