BNC

BNC (Bayonet Neill–Concelman) is a miniature quick-connect/disconnect coaxial RF connector widely used in professional video, broadcast, and test equipment. It features a bayonet-style locking mechanism that mates with a quarter-turn, providing a secure connection that resists accidental disconnection. In the context of CRT monitors and televisions, BNC connectors are primarily found on professional and broadcast-grade equipment carrying composite video, S-Video (as dual Y/C BNC pairs), and component video signals, as well as RGB signals on high-end monitors.

History

The BNC connector was developed in the late 1940s as a smaller, more convenient version of the existing Type C connector. It was named after its bayonet locking mechanism and its two inventors: Paul Neill of Bell Labs (who also invented the N connector) and Carl Concelman of Amphenol (who invented the C connector). The connector was originally designed for military radio and radar systems during World War II. In 1944, the US Navy standardized the design and designated it "Type BNC" (Baby Neill Constant), assigning military part numbers UG 88/U (male) and UG 89/U (female).

After the war, BNC connectors gained widespread adoption in commercial applications due to their excellent RF transmission characteristics, compact size, and quick-connect convenience. They became a standard connector in professional video and broadcast studios, test and measurement equipment, and telecommunications.

Design

The BNC connector uses a two-stud bayonet coupling mechanism that locks with a quarter-turn rotation, allowing rapid connection and disconnection while maintaining a reliable electrical contact. It is designed as a constant-impedance connector, meaning the characteristic impedance remains consistent across the entire connector, minimizing signal reflections.

BNC connectors are manufactured in two impedance versions: 50Ω (used primarily for RF, data transmission, and test equipment) and 75Ω (used primarily for video signals, including composite, SDI, and HD-SDI). While the two versions can physically mate with each other, impedance mismatches above 10 MHz can cause signal reflections and degradation. For video applications on CRT equipment, the 75Ω version is the correct choice.

Specifications

Parameter	Value
Impedance	50Ω or 75Ω
Frequency range (50Ω)	DC to 4 GHz (up to 10 GHz for specialized versions)
Frequency range (75Ω)	DC to 2 GHz
Maximum voltage	~500V RMS
Coupling mechanism	Bayonet (quarter-turn)
Common cable types	RG-59/U (75Ω), RG-6/U (75Ω), RG-58/U (50Ω)
Standards	IEC 61169-8, MIL-PRF-39012

Use on CRT Equipment

BNC connectors are the standard video connector on professional and broadcast CRT monitors, where signal integrity is paramount. Common configurations include:

• Single BNC jack — carrying composite video (75Ω), replacing the RCA connector used on consumer equipment
• Dual BNC jacks — carrying S-Video as separate Y (luminance) and C (chrominance) signals, common on professional S-VHS equipment and patch panels
• Three BNC jacks — carrying component video (Y/Pb/Pr)
• Four or five BNC jacks — carrying RGBS or RGBHV signals on high-end production monitors (e.g., Sony PVM/BVM series)

On professional monitors such as the Sony PVM and BVM lines, JVC TM series, and Ikegami and Panasonic broadcast monitors, BNC connectors are used for virtually all video inputs and outputs. Many of these monitors also feature loop-through BNC outputs with 75Ω termination switches, allowing signals to be daisy-chained between multiple monitors.

Consumer CRT televisions rarely feature BNC connectors, though adapters between BNC and RCA are widely available and commonly used to connect consumer-grade sources to professional monitors.

See Also

• RCA (connector) — Consumer-grade A/V connector, easily adapted to BNC
• Mini-DIN-4 — Connector used for S-Video
• Composite (CVBS) — Analog video signal commonly carried over BNC in professional settings
• S-Video (Y/C) — Separate Y/C video signal, sometimes carried over dual BNC