Radio antennas match the low impedance of a receiver to the high impedance of the free space medium through which radio waves percolate. Telescoping radio antennas are linear, retractable and are commonly used for radio devices, automobiles and cellular technology.
Most telescopic radio antennas are composed of a conductive metal or alloy easily fitted on a mount routed to the transmitter/receiver. For the antenna to retract and extend, the telescopic antenna is designed in segments, unlike the whip antenna which is a singular metal rod. Various metal-smithing tools are used to shape and hone the segments.
Antennas are designed at a certain length and rod diameter and are tuned to match the frequency of the connected radio. Generally, radio antennas for short wave broadcasters (such as FM) are cut at least a quarter the size of the broadcasted wavelengths. In basic radio theory, antennas rely on Ohm's Law and reciprocal transmission laws to determine rod length based on frequency range.
Once the length is determined and the segments are cut, each segment is fitted to allow retraction and extension without impacting current capability and reception quality. The telescopic antenna is then mounted to the clip or fitting and routed to the receiver/transmitter based on use and overall design.