A BNC (Bayonet Neill-Concelman) coupler is a type of RF connector used to join two BNC-terminated cables or to connect a BNC cable to a device with a BNC port. It features a bayonet locking mechanism, which allows for quick and secure connections with a simple twist, making it popular in applications where frequent disconnections are required. BNC couplers are widely used in video surveillance, telecommunications, test and measurement equipment, and broadcast systems, operating at frequencies up to 4 GHz, though some high-performance models can handle up to 11 GHz.

The design of a BNC coupler includes a central pin (male) and a outer shell with bayonet lugs (female), which mate with corresponding features on BNC connectors. The coupler ensures proper alignment of the inner conductors, minimizing signal loss and impedance mismatch. Most BNC couplers are 50 ohms or 75 ohms, with 50-ohm versions used in RF and data applications, and 75-ohm variants in video systems to maintain signal integrity for analog or digital video signals, such as CCTV or broadcast video.

Materials used in BNC couplers include brass for the body, with gold or nickel plating to enhance conductivity and corrosion resistance. The dielectric material, typically Teflon or polyethylene, provides insulation between the inner conductor and the outer shell, ensuring stable electrical performance. Some couplers are designed with a bulkhead mount, allowing them to be mounted on panels or enclosures, while others are inline, used to extend cable lengths.

Advantages of BNC couplers include their ease of use, reliable connection, and durability. The bayonet locking mechanism prevents accidental disconnection, even in vibrating environments, such as in vehicles or industrial machinery. They are also compatible with a wide range of BNC connectors, making them versatile for various systems. In test and measurement applications, BNC couplers with low insertion loss (less than 0.3 dB) are preferred to ensure accurate signal measurement, while in harsh environments, weatherproof BNC couplers with rubber gaskets provide protection against moisture and dust.

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