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What is a BNC Connector? [Explained]

What is a BNC Connector

Bayonet Nut Coupling is what “BNC” stands for. It is a plug-and-socket connector extensively used in the audio, video, and networking industries.

It establishes a safe and reliable connection for a wide range of coaxial cable varieties and maintains the same characteristic impedance of the cable, with 50 and 75 ohms.

It is usually used for video and radio connections up to about 2 GHz and 500 volts. However, above 4 GHz, the slots may radiate signals because it uses a dielectric at their ends. With the losses, the connector is still usable, up to about 11 GHz.

The connector has a twisting lock design with two hauls in the female portion of the connector, which strongly engages the slot in the shell of the male portion.

Once you insert the plug into the socket and rotate it, it will automatically cause the pins in the socket to be pinched into a locking groove on the plug. This prevents the plug from being removed from the socket and secures the connection.

History of BNC Connector

The connector is named after its inventors, Bayonet Neill and Carl Concelman. The central theme is the locking mechanism, after which the connector is named the Bayonet mount mechanism.

It was first introduced on military radio equipment in the early 1940s and has become widely used in radio systems and video connections.

They were also commonly used for early computing networks, including ARCnet, the IBM PC, and the variants of Ethernet.

Other applications include analog and serial digital interfaces, video signals, radio antennas, aerospace electronics (avionics), and nuclear instrumentation test equipment.

Types of BNC Connectors

There are two types of BNC Connectors, and both appear almost identical with slight variations in dimension. However, both have specific uses and compatibilities but can somehow be interconnected.

It is important to know that Reverse-polarity BNC, also called RP-BNC, is a variation of the BNC that reverses the polarity of the interface. In Reverse-Polarity the female contact normally found in a jack is usually in the plug, while the male contact normally found in a plug is in the jack.

The two types are,

1. 50 ohms Version

The 50 ohms connectors are more miniature in dimension than the 75 ohms connectors and are typically designed to use at frequencies up to 4 GHz. These connectors are mainly used for data and RF.

2. 75 ohms Version

Though unreliable identification points, these types sometimes have absent dielectric in the mating ends, which helps them to be recognized by experienced individuals.

75 ohms version is designed to be used at up to 2 GHz frequencies for optimal functioning.

75 ohms connectors are primarily used for HD Video signals and DS3 Telco central office applications. Moreover, VHF receivers used 75 ohms antenna inputs, often using the 75 ohms BNC connector.

It is essential to know that smaller versions of the BNC connector, often called Mini BNC and High-Density BNC (HD BNC), are used for HD video applications. These connectors also have 75 ohms impedance. Interestingly, they have smaller sizes with a higher packing density on circuit boards and equipment backplanes but retain the electrical characteristics of the original specification.

Compatibility of BNC Connectors

The two types, 75 and 50 ohms of BNC Connectors are designed to mate with each other non-destructively; both comply with the 2007 IEC standard.

BNC connectors were initially made only in 50 ohms versions for use with any cable impedance. Above this frequency, however, the mismatch becomes progressively more significant and can lead to signal reflections.

At frequencies below 10 MHz, the impedance mismatch between 50 ohms and 75 ohms connectors and cables is negligible. 

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