- Professional antenna installations that require the drilling of holes into automobile roofs or trunks, or that permanently attach support devices to bumpers, trunks and fenders, are often replaced by non-invasive magnetic mount antennas. Their use prevents the unsightly hole where an antenna was installed and consequently preserves the automobile's resale value. Magnetic mounted antennas which attach simply and securely to metal automobile bodies with their strong magnets, are thus easier to install and to remove, and are quickly transferable to other automobiles without modifications.
Often, an automobile's metal body is incorrectly assumed to be the necessary electrical "ground plane" that an antenna requires for operation, when actually it serves as a capacitor which is an important electrical component between the antenna and the ground beneath the car. The antenna must therefore be coupled securely to the automobile's metal body in order to establish the necessary capacitance, which is a measure of the electrical charge that the antenna system can store. That coupling is best achieved by ensuring that the part of the automobile where the magnetic mount will be attached is clear of dirt and grease that would otherwise impede the magnetic coupling. If, however, for any reason that magnetic coupling was somehow prevented, the required capacitance necessary for proper operation would then be made by the electrically-conductive foil that is attached to the coax cable's shield at the bottom of the antenna. - Mounting the antenna on the automobile's largest available metal surface ensures the best possible performance. This causes most magnetically mounted antennas to be attached to the car's roof or trunk. The best electrical performance of the antenna is achieved by placing its magnetic mount in the middle of the roof or trunk.
The antenna is then connected to the radio, cell phone or other component that uses beamed-in information with quality, low-loss coax cable. This cable can be run behind and under the trunk lid, through a window or in certain instances through an inductive coupler through the car's glass. Care must be taken not to crimp the coax cable unnecessarily for fear of breaking its internal insulating layer and possibly causing a short circuit between the conducting core and its surrounding shield.
Transmission and reception quality can also be adversely affected by cable length. When excess coax cable from the antenna to the radio is not removed, the signal quality will suffer from cable-run loss. Conventional wisdom has therefore always dictated that the antenna cabling be kept as short as possible.
Signal-quality degradation that is caused by weather-induced cable-connection fouling can be prevented or at least minimized by regular inspections and contact cleaning and retightening. When vibrations from the automobile's operation loosen the cable connection at the antenna mount, and rain or snow cause oxidation in that connection, the signal will suffer dramatically and can be lost entirely.
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