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Impedance is complex opposition to alternating current: it includes resistance and a frequency-dependent reactance. Antenna input impedance is therefore more than a DC resistance reading.

Coaxial cable carries a signal using an inner conductor and a concentric outer conductor. The dielectric and construction determine characteristic impedance, losses and propagation speed.

SWR is the ratio of maximum to minimum voltage on a line with standing waves. It is related to reflection caused by an impedance mismatch.

The familiar 20-log voltage conversion represents a power ratio only when impedances are equal.

Radial angle and surroundings affect the feed impedance; the drawing does not replace tuning.