![]() Located on the roof, you are shielded and not in the main lobe of horizontal radiation. Location is crucial not only for proper operation but also for operator safety exposure to RF radiation. So forgiving, you can get away with the center of the trunk lid on an automobile. UHF or 70 cm is more forgiving with roughly a 1-foot diameter ground plane requirement. It does not give you much room to work with to move the antenna around off-center and maintain at least a ½-meter from any roof edge. 2-meter antennas are the least flexible in mounting location because it has the largest ground plane requirement of 1-meter diameter. The rooftop is the only flat horizontal surface on a vehicle, large and high enough to act as a ground plane. The correct location is the roof of a vehicle. It will contain common-mode currents preventing it from backing up into the vehicle wiring, causing possible vehicle electronics malfunction, aka RFI. The coax length between the radio and antenna is at a minimum ¼ wavelength long or longer. If installed in the wrong spot, the consequences are not as severe. Mobile antennas for commercial LMR and Public Safety services are not compromised unless installed incorrectly in the wrong location. You are no longer limited to amateur-made products for HF. Once you move up to VHF and UHF frequencies, it opens doors to commercial antenna manufacturers that offer amateur band antennas. On the other hand, with VHF, it is possible to install an antenna without compromises, and UHF is straightforward. It has to go somewhere to balance out currents. Without a proper ground plane, there will be an RF current on the coax shield and all the vehicle wiring. At best, you can make it somewhat usable. Therefore common-mode current is guaranteed to be an issue you can never eliminate. No way around it, as it is impossible to establish a proper ¼-wave ground plane and whip lengths. Any HF antenna made for a vehicle is a compromised design with poor efficiency. ![]() Take whatever K0BG says with a grain of salt he means well but does not understand modern vehicle electrical systems.Īs already stated, K0GB refers to an HF antenna and has nothing to do with VHF and UHF applications. I know this thread is a bit dated, but here are my two cents worth as an amateur and professional. If you have a full size pickup the rear stake holes will be more than a wavelength from the cab at 2m however you will still get Reflections from it. The metal structure of the cab drastically interferes with your radiation pattern and your match. If you use the holes close to the cab these run into the same issues as a trunk mount car antenna. Okay: Stake hole mounts I don't have a great deal of experience with. Route the cable in such a way that water won't drip in and it won't get smashed by the door as often. ![]() A similar mounting point to the one above should be chosen. Good: If you are using a magmount, the ground plane is parasitic back to the radio chassis mount. This would be an effort to maximize the amount of ground plane around the antenna, and to minimize the amount of directivity that the shape of your ground plane will provide your signal. If you are just planning on the one antenna you should try to get it close to the center front back left right. The main things that impact the information below would be a ladder rack or a metal cover.īest: If you are planning on through hole mounting to the center of your roof deck, the ground plane will be physically established where the connector comes through the roof. Accessories that you might have for your truck will change the below information. They are not worse than motorcycles however. Trucks have some suboptimal mounting locations. Mobile installation is almost always fully unbalanced. However as the linked article in the comment explains you will be fully unbalanced. You don't mention what type of antenna you have or where on the truck you are mounting it. At VHF and UHF frequencies the ideal antenna length between the ends of the band is not that great.Ī feedline choke can be installed on any antenna but unless you are planning on driving a wire brush you're not going to get much induced current in your feed line. VHF and UHF transmission bands are each wider than a single HF band but not wider than all of the HF bands grouped together. The purpose of a screwdriver antenna is to lengthen or shorten the element to match the wavelength of your transmission band. The article you reference has to do with protecting the controller in a screwdriver antenna.
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