Filling in the gap.
Most ham radio enthusiasts who focus on off grid operations spend a lot of time working with solar panels, batteries, generators, and similar equipment with the end goal of having a fixed-or semi-fixed base station. Whether that station is a permanent installation, such as in a house, or a temporary location, such as a cabin or camp site, the principle is the same: the station is not meant to operate while in motion. Another option many hams overlook is mobile operation. It’s worth consideration because mobile ham radio fills in many of the holes left by fixed and semi-fixed stations.
I don’t have firm data, but in my experience mobile operation isn’t nearly as popular as it used to be. When I was first licensed in the 1980s, it seemed everyone had a mobile rig! Today, outside of VHF/UHF, I hardly ever QSO with a mobile station.
Antenna issues.
Perhaps the biggest challenge of a mobile/vehicle station is the antenna. Operators are faced with having to come up with an antenna that works and looks good on the vehicle. Since the metal in the car acts as a ground plane, antenna placement will effect the radiation pattern.
In general, the signal will favor the largest mass of metal. For example, if an antenna is mounted at the rear left side of the car, the radio signal will favor the front right of the car. So if you want an even omnidirectional pattern, mount the antenna in the center mass of the vehicle.
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As one might guess, the location for best performance and location for best appearance may not be the same thing. Unfortunately, the laws of physics make no exceptions for style. As with all things in off grid ham radio, there will be tradeoffs.
Many cars today have a lot of plastic body panels that make establishing a good ground plane difficult. Once again, there are tradeoffs. The only real option in this case is to bond the coax shield to the frame of the car.
Be aware that there is a difference between bonding and grounding. Grounding means a device to connected to the earth. Bonding means two separate points or devices are connected together so that they have the same electrical potential. This distinction doesn’t make a lot of difference in the context of what we’re discussing here, but it is worth mentioning.
Radio mounting considerations.
Back in the “good old days” we could just bolt our radios under the dash with a simple metal bracket and call it good. Today, car interiors are mostly plastic, have more elaborate features, extensive ventilation systems, and multiple airbags. All these things make mobile ham radio much more challenging. Look in any recent-vintage model car. It’s hard to identify a place that isn’t disqualified by one of the preceding situations.
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There are solutions. Option one is to mount the radio in the compartment between the seats with Velcro. An under dash or similar surface mount with Velcro is possible too. Disadvantages: If you go with the storage compartment, be aware the enclosed space may create ventilation/overheating problems. Mounting it elsewhere with Velcro, while functional, will likely look like crap.
Option two: Mount your radio in a go box configuration (or maybe you already have a go box) and bring it along in the car. There’s no reason a go box can’t do double duty as a mobile unit. Disadvantage: Most go boxes include equipment not needed for a mobile application, so you may be dragging along a lot of extra gear. This extra gear may take up space needed for passengers and cargo.
Option three: There are numerous permanent and semi-permanent mounts available on line. These run the range from simple spring clamps designed to fit in cup holders to somewhat expensive permanent mounts. One of the most popular is Ram mounts. For the unfamiliar, Ram mounts are customizable ball-and-socket adjustable hardware. There is also Bulletpoint Mounting Solutions, very similar to Ram, offering a complete system that allows for multiple devices. Both Bulletpoint and Ram have vehicle model-specific hardware that works very well. In addition to radios, they can be used for cellphones, cameras, iPads, and similar devices. I have a Bulletpoint in my Jeep; it’s rock solid and looks great. Disadvantages: They are expensive, and since they are often model-specific, if your car is not one of the vehicles they support, you may be out of luck.
Powering your mobile ham radio.
What it will take to get power to your mobile rig varies depending on the radio. If you’re running a handheld or QRP radio, you’ve got it easy. Just plug into the 12 volt power port already in your car and you are all set.
If you need more current than can be pulled out of a factory power port, then you’ll have to run some wiring in your car. Some hams terminate their installations on the vehicle fuse block. It’s more preferable to run wiring directly to the battery.
A few factors to consider:
First, use the appropriate size and type of wire. For mobile radio applications, wire is deployed in an uncontrolled environment with excessive heat, cold, moisture, and vibration. Make sure the wire you use is certified for these conditions. Wire used for residential electric is not acceptable.
Second, focus on fire safety. Power leads should at a bare minimum have a fuse on the positive wire as close to the power source as possible. A much better design is to place a fuse on the positive and negative lead, with one fuse near the power source and one fuse near the device, for a total of four fuses.
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Multiple radios and devices: If you have more than one radio or device, ideally you would use a DC power distribution block such as a West Mountain Radio Rig Runner. Now-defunct MFJ made some great DC power blocks too; you should be able to find some still out there. Automotive wire taps are acceptable for one, possibly two devices. Any more than that and you’ll probably end up creating a jumbled mess of wire. Make sure each radio has its own set of fuses; West Mountain and MFJ power distribution blocks already have built in fuses for each branch.
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Don’t kill your battery.
One convenience of connecting your radios directly to the battery is that you can use them even if the car isn’t running. The disadvantage of course is that you risk discharging your battery to the point your car will not start.
There are three ways to deal with this. First, the operator can simply manually monitor their power use and don’t let the battery voltage drop too low. Without a voltage monitor, this is pure guesswork. If you will not be operating with the car engine turned off for more than a few minutes at a time, then you can probably get away with this method.
The second way is to install a low voltage cutoff switch. These switches are somewhat inexpensive and easy to install. You don’t have to monitor your own power use. If the voltage drops too low, the switch will automatically cut power to the radios.
Lastly, there are battery isolators. How these work is you power your radios with an auxiliary battery (not the vehicle battery). When the car is running, the isolator allows the auxiliary battery to charge off the car. When the car is not running, the isolator cuts the connection between the batteries and the radios draw power from the auxiliary battery only. If you run down the auxiliary battery, the car will still start an operate normally. West Mountain Radio sells an isolator, and there are less expensive versions on Amazon.
Final thoughts.
Mobile ham radio is a form of off grid radio that opens possibilities to operators who may have no other options outside of a traditional grid-based station. Although going mobile is more complicated than it used to be due to advanced features and materials used in modern cars. with some planning and forethought a ham can overcome these challenges and create a useful, functional mobile ham station.