A radio antenna which can be readily tuned to the exact frequency of operation, easily coupled to a coaxial feed-line with minimum standing wave ratio and/or which is normally vertical and can be used where horizontal space is at a premium, such as: indoors or on boats. The antenna has a center loading coil, the inductance of which is adjusted by means of a split coaxial sleeve axially moveable relative to the coil. The input impedance of the antenna is adjusted relative to the impedance of the feed-line by means of a coupling transformer, the transformation ratio of which is controlled by means of a coaxial split metal sleeve axially adjustable relative thereto. A coaxial cable wound into a coil around a ferrite core attenuates the high ratio frequency voltage on the end of the antenna to the feed-line. For indoor use, the antenna is housed in an extensible tubular housing which can be extended to engage the ceiling and floor of a room to hold the antenna in vertical position.