Going mobile? Installing a ham radio station in your vehicle expands the usefulness of amateur radio, making automobiles ham shacks on wheels. It’s a convenient way to have instant emergency communications onsite without any tedious setup. You can even treat yourself to park and POTA—no picnic table needed.
Those of you who have moved to mobile radio operation probably started with combination VHF/UHF radios. Some go the extra mile and later add HF radio to the mix. Either way, ham radio mobile installations can present some unique challenges for the operator. Anyone who has shopped for a car or truck in the last 20 years has found that Detroit took away a lot of the radio space that we can utilize. Yet, we still adjust and improvise.
There are many different ham radio mobile equipment combinations and installation approaches that can result in an efficient mobile station. Every ham radio mobile station is a compromise, but you can do things to improve both operating flexibility and range, no matter what vehicle you drive.
Interior Setup
Few amateurs search for a new vehicle with the idea of creating a mobile station in mind. In most cases, they already own a vehicle and decide to operate mobile. Either scenario presents its own set of issues. Minivans, SUVs, RVs, Jeeps, station wagons, crossovers, and plastic/fiberglass bodies present challenges.
One of the most useful features found in some mobile rigs is the remote head, which allows you to separate the controls from the radio and save space. Choose a mounting location that will put your remote head within easy reach and be easily viewable. The best rule of thumb for every mobile installation is to secure your equipment properly. You don’t want a flying station in the event of a panic stop—or a collision.
One example of a secured solution is the Lido LM-300 Gooseneck Mount that attaches to the seat bolt, allowing the remote head to be easily adjusted. Cup holder mounts like the heavy-duty Lido LM-820 expand to fit by twisting the base, establishing a friction fit. It also has a swivel to adjust arm position.
Sometimes you’ll find that what you need came with your radio. My Yaesu FTM-400 Mobile Transceiver had a mounting bracket for the remote head. Everything fit in a cubby located on the dash side of the console, secured by two small sheet metal screws and industrial strength Velcro. Another good solution I’ve seen recently is a mount that clips into the seams of the dashboard.
Based on personal experience, suction cup mounts aren’t always reliable, especially in the heat. Vent clip mountings vary greatly in quality. Better ones have adjustable tensioning and secure both on the horizontal and vertical planes. Forget the double-sided super-duty tape. Sometimes it holds, sometimes it doesn’t, and it can be difficult to clean after removal.
The radio’s main body should be mounted in a location with proper airflow around the entire unit. Avoid closed areas like tight cubby holes, center consoles, glove boxes, trunks, and storage boxes. Open areas in the rear of SUVs, mini/full-sized vans, and hatchbacks are acceptable as they maintain the same temperature as the rest of the interior. Under passenger seats is a popular mounting location for the radio body—just be sure not to disturb any existing wiring.
Sound Advice
Install an external mobile speaker—it will make the audio much clearer and easier to hear, especially if you have the radio mounted under the seat or back in the cargo area. They don’t have to be high-fidelity, but you want clear audio at voice frequencies.
Speakers like bhi’s DSP NES10-2MK4 and West Mountain Radio’s WMT-58407-948 ClearSpeech DSP Noise Reduction model increase audio levels and noise canceling technology. Remove noise and interference and crank the volume to overcome road noise.
My car has an auxiliary input so I can connect the audio out from my rig to the car stereo. This way, the audio comes out the car speakers and I can use my steering wheel controls to adjust the volume. I can even adjust the tone from the radio controls to make it sound better than the built-in speaker.
Best Antenna Locations
Antenna location makes all the difference. Regardless of where you mount one, it’s the metal mass directly under the antenna that counts, not what’s alongside. Increasing the antenna height may also increase distance, so mount your antenna as high as possible.
The center of a vehicle’s roof is a very good place to mount a VHF/UHF antenna. However, creating an optimal ground in this position involves drilling a hole. If you choose this path, seek professional help from your dealer or a qualified installer. You could use a mag mount instead, but the only ground path is through capacitive coupling, which is lossy in comparison.
Trunk mounting is second best. It’s probably the easiest location to place VHF/UHF antennas, loaded UHF/VHF/HF antennas, and small screwdriver antennas like the Diamond SD330 3.5-30 MHz model. Seam mountings and clip mountings are commonly used here, but it’s important to make sure they are well grounded (bonded) to the frame. If your vehicle doesn’t have a trunk or rear hatch, the front fenders or cowl areas are good alternatives.
Locations like bumpers, trailer hitches, and ball mounts on the rear quarter panels round out the list. They’re the solution for tall antennas like a 102-inch whip, Hustler HF Mobile System, large screwdriver antennas, and hamsticks.
With screwdriver antennas, you’ll want to keep as much of the coil in the air—above the metal— as possible. Putting the coil right up against the body will result in greater losses. If you have a pickup truck, mounting in the middle of the center of the bed with the coil raised has proven to be a good strategy.
The Long and Short of Antennas
One of the most important mobile purchases you’ll ever make is the antenna. Choosing the right antenna can help improve your reception and transmit range.
When you’re shopping for VHF/UHF mobile antennas, don’t take the dB gain figures as fact— think of them more as a guide. Yes, most of those antennas will have some gain to them, but how and where you mount it will affect its performance. You’re better off with an effective mounting location instead of just comparing dBs of gain, so choose the best antenna to fit your needs over its specs.
Longer antennas may perform better. But consider this—a 1/4 wave VHF/UHF has a relatively high angle of radiation, making it easier to reach radio communication sites located in higher places, like repeaters. So they’re more useful in mountainous and metropolitan areas with tall buildings. A 5/8 wave antenna radiates and receives more energy toward the horizon and can have up to a 2-3dB gain over a 1/4 wave. They’re best used in the flatlands and suburban areas.
HF antennas are a different animal. All of them are a compromise to some extent, especially on 80 and 40 meters. All of them will allow you to make contacts—even DX QSOs. But their efficiency, overall length, quality, design, sturdiness, and ease of mounting will vary. The most important thing to look at is overall antenna efficiency, your specific needs, and how the antenna can be mounted on your vehicle.
Many HF mobile antennas require some kind of impedance matching to obtain a reasonable SWR. Overall length is also important in obtaining good efficiency, but there are practical limitations for antenna height and placement on vehicles. Driving around with a 33-foot vertical radiator for 40 meters would be silly—and dangerous.
Probably the most efficient HF mobile antenna is a Texas BugCatcher, followed by the screwdriver (easiest to operate), Outbackers and similar multibanders, single-band Hustler, hamsticks, and base-loaded antennas, in that order.
Common Mode–Common Problem
There will always be some level of common mode current flow in any mobile installation. That’s because there is always ground loss, even at VHF/UHF frequencies. The more ground loss, the higher the level of common mode there will be. Causes include poor antenna mounting techniques, such as using magnet mount antennas or clip mounts on the hood, trunk, or luggage rack. Trailer hitch and bumper mountings can increase common mode significantly.
Proper choking of these currents must be done to help improve your signal to noise ratios (SNR). Using ferrite cores (Mix 31) is essential in minimizing RFI produced by today’s vehicle microcontrollers. Vehicle wiring doesn’t always provide enough slack to install multiple-turn toroid cores. Under these conditions, use multiple snap-on cores if there is enough wire space available.
Don’t forget chokes on power connections to the radio. You’ll also want two chokes on the feedline—one right at the antenna and a second where the feedline enters the vehicle. The one at the antenna is especially important if you’re using a screwdriver antenna.
Bonding
We’re not referring to 007 here. This kind of bonding involves making low impedance connections among the conductive parts of your vehicle to make a workable ground plane.
To improve RFI noise reduction and antenna efficiency, bond horizontal body surfaces together, such as the hood and trunk to the rest of the vehicle body. This is done by attaching short pieces of tinned copper braid across the hinge connections of the hood and trunk. The braid connection helps to electrically join these surfaces into a single massive ground plane. For pickup trucks you may also improve the ground plane by bonding the bed to the cab, using braid segments underneath the truck and utilizing existing bolts as connection points.
Also consider grounding the exhaust system on cars and trucks, which can act like an antenna. Electrically bond your exhaust pipe to the vehicle frame at three or more points, spread out along its length. Attach the braid to the pipe using clamps and use screws with star or tooth lock washers and soldered ring connectors to ensure a good connection to the car body or frame. Ready-to-install kits specifically for exhaust system grounding are available, or you can homebrew your own.
Pulling it Together
Remember, the primary goal is to maximize the ground plane under the antenna and to improve the conductivity at RF frequencies. This alone will help control many of the issues with mobile operation.
