| 摘要 |
A frequency adjustable radio antenna attachable to an exterior portion of a motor vehicle has an effective resonant wavelength which may be varied from a remote location; e.g., a transceiver located within the vehicle, to selected values includes a hollow conductive base mast electrically insulated from a mounting bracket and a radio frequency connection to a transceiver, an elongated hollow cylindrical coil housing attached coaxially to the upper end of the base mast and an upper circular cap attached to the upper end of the coil housing in coaxial alignment therewith. The housing is made of an electrically non-conductive material and has formed in inner cylindrical wall surface thereof an elongated helical groove which holds a tuning coil coaxially enclosing a disk-shaped commutator which has a resilient outer surface longitudinally slidably contactable with inner conducting surfaces of convolutions of the coil. An electrical motor and lead screw mechanism within the hollow interior space of the base mast raises or lowers the commutator in response to external command signals to contact selected coil convolutions. In one embodiment, an upper electrically conductive extensible mast section holding an elongated antenna whip is coaxially and slidably held within the upper cap insulated from the coil but in electrically conductive contact with the commutator, thus interposing more or less coil convolutions between the upper mast and the base mast, which is in electrical conductive contact with the lower end of the coil, thereby resonating the antenna at lower or higher frequencies, respectively. In another embodiment, a conductive whip is fixed in a cap attached to the top of an insulated coil housing and is electrically connected to the upper end of a tuning coil within the housing, and remains stationary. A commutator disk at the upper end of a conductive shaft is raised or lowered to interpose less or more turns between the conductive shaft and the whip to tune the antenna, which includes an RF de-coupler that has an annular ring-shaped spring member that has a resilient inner circumferential surface in longitudinally slidable contact with the outer surface of the conductive shaft, and an outer surface in electrically conductive contact with the lower end lead of the coil and a mast, thus shorting out the lower portion of the coil and thereby suppressing harmonics or sub-harmonic currents from being induced therein.
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