Cables and connectors

Cables and connectors form the physical layer that carries signals and power between electronic equipment. A cable is a controlled arrangement of conductors and insulation, and a connector is the standardised plug and socket that joins one cable to another or to a device. Although they may seem simple, the construction of a cable strongly affects how faithfully a signal arrives, especially at high frequencies or over long distances, where losses, reflections and interference become significant.

Several cable families serve different needs. Coaxial cable surrounds a central conductor with an insulating layer and a braided shield, giving it a defined characteristic impedance and good rejection of interference, which suits radio-frequency and video signals. Twisted-pair cable, used widely in computer networking and telephony, twists conductors together so that interference picked up by the pair largely cancels; it comes unshielded (UTP) or with added foil or braid shielding (STP or FTP). Fibre optic cable abandons copper altogether and carries signals as pulses of light along a glass fibre, immune to electrical interference and capable of high bandwidth over long distances.

Two ideas recur across cabling. Impedance matching ensures the cable's characteristic impedance suits the equipment, so power transfers cleanly and signals are not reflected at junctions. Shielding and grounding guard against electromagnetic interference and the hum that can otherwise contaminate audio and video. Connector and wiring standards, such as the TIA/EIA 568A and 568B schemes for network cabling, define exactly which conductor goes to which pin so that equipment from different makers works together reliably.

Frequently asked questions

Why does cable impedance matter?

Matching a cable's characteristic impedance to the equipment allows power to transfer efficiently and prevents signal reflections at junctions, which is important at higher frequencies.

How does twisting wires reduce interference?

Twisting the two conductors of a pair means interference is picked up almost equally by both, so it largely cancels when the receiver looks at the difference between them.

What advantage does fibre optic cable offer?

Because it carries light rather than electrical current, fibre is immune to electromagnetic interference and can carry high bandwidth over long distances with low loss.