Telescopic Antenna

an antenna whose receiving or radiating elements, such as the arms of a dipole, are made in the form of an extensible system of metal tubes or rods of approximately equal length. Such a design facilitates changing the length of the antenna elements during tuning and permits the size of the antenna to be reduced when it is not in operation—for example, during transport or storage.

For each pair of telescoping tubes, the interior diameter of the outer tube is approximately equal to the exterior diameter of the inner tube. The tubes fit into one another with some friction, which is needed to provide electrical contact and to maintain the required length of each element of the telescopic antenna under operating conditions—that is, under the action of gravity or exposure to shaking or vibration. In some cases the required position of the tubes may be fixed by additional means. For example, collet chucks or springs may be employed.

Telescopic antennas are used principally in conjunction with radio receivers, radio transmitter-receivers, portable television receivers, and television receivers installed in moving objects, such as automotive vehicles; such antennas are also used as indoor television antennas.