RF cabling and connectors

Radio-frequency cabling carries high-frequency signals between transmitters, receivers, antennas and test equipment, and at these frequencies a cable behaves as a transmission line rather than a simple wire. The dominant type is coaxial cable, in which a central conductor runs along the axis of a tubular outer shield, separated by an insulating dielectric. This geometry confines the electromagnetic field between the conductors, shields the signal from outside interference and gives the cable a well-defined characteristic impedance set by its dimensions and dielectric, commonly 50 ohms for radio work and 75 ohms for video.

The central idea in RF cabling is impedance matching. When the impedance of the source, the cable and the load (such as an antenna) all match, energy travels along the line and is fully delivered. A mismatch causes part of the signal to be reflected back toward the source. The forward and reflected waves combine to form a standing-wave pattern along the line, and the severity of the mismatch is described by the voltage standing-wave ratio (VSWR): a VSWR of one to one means a perfect match, while higher values indicate more reflected power and less delivered to the load.

Reflections and mismatches waste power and can stress a transmitter, so RF connectors and cables are made to maintain a consistent impedance through every junction. Connector families designed for radio frequencies preserve the coaxial geometry across the join to keep reflections low. Cable loss also rises with frequency, so for a given link the cable type and length are chosen to keep both attenuation and VSWR within acceptable limits.

Frequently asked questions

Why is coaxial cable used for RF signals?

Its shielded geometry confines the field between the inner and outer conductors, rejecting interference and giving a defined characteristic impedance that suits high-frequency transmission.

What does VSWR measure?

The voltage standing-wave ratio indicates how well a load is matched to the line; one to one is a perfect match, and higher values mean more power is reflected rather than delivered.

Why does impedance matching matter at radio frequencies?

A mismatch reflects part of the signal back toward the source, wasting power, creating standing waves and potentially stressing the transmitter.