An adjustable mobile antenna comprising a dielectric rod several feet in length, a loading coil comprising a conductive wire helically wound in close fashion along an upper portion of the length of the dielectric rod, a protective outer insulator jacket covering the loading coil and a major portion of the dielectric rod, and a dielectric sleeve mounted on the outside of the protective jacket and slidable thereon along the length of the loading coil to effect "dielectric loading" of the loading coil to control the frequency of the antenna.