| 摘要 |
A frequency adjustable radio antenna includes a conductive whip on an insulated cylindrical coil housing electrically connected to the upper end of a tuning coil within the housing. A commutator attached to a conductive shaft is raised/lowered to interpose less/more coil turns between shaft and whip to tune the antenna. An RF de-coupler slidably contacts the shaft, and electrically contacts the lower end of the coil and a conductive mast which supports the housing, thus shorting out lower portions of the coil to suppress harmonic currents from being induced therein. A method for making the coil includes winding wire onto a mandrel in a first direction, sliding a housing over the windings, and rotating the mandrel in an opposite direction to cause coil convolutions in a helical mandrel groove to increase in diameter and thereby spring out of the mandrel groove and into a helical coil housing groove.
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