What Are BNC & RCA Cables?by Scott Shpak
Connectors for audio and video systems once fell into professional and consumer divisions with little overlap between connector styles. Prosumer-class components have blurred the lines and mixed the hardware, increasing the need for adapters to tie mixed systems together. BNC and RCA connectors combine with coaxial cables to deliver video, with enough crossover that BNC-to-RCA adapters are common.
Bayonet Neill-Concelman connectors -- sometimes called British Naval Connectors -- are distinguished by metal casings on the ends, with a rotating ring on the male jack. Using a BNC connector requires aligning two pins on the female plug with two openings on the jack and turning the rotating ring clockwise a quarter-turn. This locks the jack to the plug, with the locking action providing slight compression, ensuring good electrical conductivity. As with coaxial cable, BNC connectors are rated for 50 and 75 ohms impedance for use with different frequency signals.
Traditionally, BNC connectors have been the choice for ham and CB radio antennas, and military and test equipment as a quick and robust locking connector. Commercial video equipment also used BNC connectors rather than the screw-on coaxial connectors used on TVs and other consumer video equipment. Networks using 10BASE2 Thin Ethernet also incorporated BNC connectors on both network cards and to mate individual cables for longer runs. BNC connectors are the choice for word clock timing signals shared between digital audio equipment for synchronization.
RCA connectors have a long association with component audio, recognizable by the protruding pin on the jack, surrounded by metal blades arranged in rings. These blades slide over the outer metal sheath of the plug, while the center pin connects through the matching hole on the plug. The connectors are held in place by friction. Unlike BNC connectors, RCA cables don't lock and may be subject to disconnection as components move. The metal contact points of RCA plugs and jacks are often gold-coated to ensure better electrical contact.
The red and white coding of RCA connectors is familiar to anyone who has connected a stereo receiver to a turntable, tape deck or CD player. A three-conductor version including a yellow connector is used in analog video applications. Red and white connectors still correspond to right and left audio channels, while the yellow cable supplies video. Component video cables use red, green and blue coding to supply analog video that provides more clarity than a single video system, but not rivaling the digital HDMI connector, which delivers video and audio as well.