Definitions

BNC connector

BNC connector

The BNC (Bayonet Neill Concelman) connector is a very common type of RF connector used for terminating coaxial cable.

Use

The BNC connector is used for RF signal connections, for analog and Serial Digital Interface video signals, amateur radio antenna connections, aviation electronics (avionics) and many other types of electronic test equipment. It is an alternative to the RCA connector when used for composite video on commercial video devices, although many consumer electronics devices with RCA jacks can be used with BNC-only commercial video equipment via a simple adapter. BNC connectors were commonly used on 10base2 thin Ethernet networks, both on cable interconnections and network cards, though these have largely been replaced by newer Ethernet devices whose wiring does not use coaxial cable. Some ARCNET networks use BNC-terminated coax.

Specifications

BNC connectors exist in 50 and 75 ohm versions. Originally all were 50 ohm and were used with cables of other impedances, the small mismatch being negligible at lower frequencies. The 75 ohm types can be recognized by the reduced or absent dielectric in the mating ends. The different versions are designed to mate with each other, although the impedance mismatch will lead to signal reflections. Typically, they are specified for use at frequencies up to 4 and 2 GHz, respectively.

NOTE. The physical sizes of the 50 and 75 ohm sockets are slightly different and can damage the "wrong" plugs.

History

The connector was named after its bayonet mount locking mechanism and its two inventors, Paul Neill of Bell Labs (inventor of the N connector) and Amphenol engineer Carl Concelman (inventor of the C connector), and is much smaller than both the N and the C connectors. Other backronyms the BNC has picked up over the years include: "Baby Neill-Concelman", "Baby N connector", "British Naval Connector", "Bayonet Nut Connector". The basis for the development of the BNC connector was largely the work of Octavio M. Salati, a graduate of the Moore School of Electrical Engineering of the University of Pennsylvania (BSEE '36, PhD '63). He filed a patent in 1945 (granted 1951) while working at Hazeltine Electronics Corporation for a connector placed on coaxial cables that would minimize wave reflection/loss.

Similar connectors

A threaded version of the BNC connector, known as the TNC connector (for Threaded Neill-Concelman) is also available. It has superior performance to the BNC connector at microwave frequencies.

BNC connectors are commonly used in NIM electronics, but they are now often replaced by LEMO 00 miniature connectors which allow for higher densities. For higher voltages, MHV and SHV connectors are typically used. MHV connectors are easily mistaken for BNC connectors and can be made to mate with them by brute force. The SHV connector was developed as a safer alternative to MHV connectors and will not intermate with ordinary BNC connectors.

In USSR, BNC connectors were copied as SR-50 (Russian: СР-50) and SR-75 (Russian: СР-75) connectors. These connectors have slightly different dimensions (as a result of recalculating from Imperial to Metric system), but are generally interchangeable with BNC, sometimes with force applied.

Twin BNC connectors use the same bayonet latching shell as an ordinary BNC connector but contain two independent contact points (one male and one female), allowing the connection of a 78 ohm or 95 ohm shielded differential pair such as RG-108A. They are capable of operation at 100 MHz and 100 volts. Twin BNC connectors will not intermate with ordinary BNC connectors.

Triaxial connectors are a variant on BNC which carry both a signal and guard as well as ground conductor. These are used in sensitive electronic measurement systems, particularly of Keithley manufacture. Early ones were designed with just an extra inner conductor, but later tri-axial connectors also include a three-lug arrangement to rule out an accidental forced mating with a BNC connector. Adaptors exist to allow some interconnection possibilities between tri-ax and BNC connectors.

See also

References

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