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BNC Connector

Vangie Beal
Last Updated October 4, 2021 1:31 am

A Bayonet Neill Concelman (BNC) connector is a miniature quick connect/disconnect radio frequency (RF) connector used with coaxial cables in a 10Base-2 Ethernet system and for video and radio frequency applications. These connectors are some of the most widely used RF connectors because they are simple to use and offer high performance.

BNC connector performance

Virtually any standard connector is able to carry current over a mechanical connection for DC and low-frequency AC circuits. Radio frequency, on the other hand, requires a connection that will minimize changes in impedance, which could generate reflection and standing waves that can cause damage. Coaxial cables can carry radio frequencies while maintaining a characteristic impedance.

BNCs are constant impedance connectors—they have the same characteristic impedance across the whole connection, equal to that of coaxial cables. This makes BNC connectors well-suited for RF applications, as RF signals traveling along a coax cable will not see any impedance changes as they pass through the BNC connector, resulting in fewer reflections and a lower level of loss.

BNCs are male-type connectors with pins at each end to connect to the primary conducting wire. They have a rotating ring outside the tube that locks the cable to any female connector. This locking mechanism prevents accidental disconnection if the cable is pulled. There are two different types of locking mechanism that achieve this secure connection:

  1. The twist and snap: this design with interlocking studs and slots is designed for quick mating. The audible ‘snap’ is meant to indicate a proper connection.
  2. TNC (Threaded Nut Coupling): this is a threaded version of BNC that uses screw threads instead of a locking pin and slot for a secure connection.

Credit: Elecbee.com, “The Difference Between BNC and TNC”

BNC connectors typically use voltages below 500 volts and frequencies below 3 GHz but can handle up to 4 GHz. Their specifications can vary according to manufacturer but the following specs are typically uniform across all BNC connectors:

  • Frequency Range: Up to 11 GHz (0 – 4 GHz with low reflection)
  • Impedance: 50 Ohms, 75 Ohms
  • Dielectric Withstanding Voltage: 1500 VRMS
  • Mating Cycles: 500
  • Temperature Rating: -65°C to +165°C
  • Diameter (Male): 14.0 mm / 0.570 in
  • Diameter (Female): 11.1 mm / 0.436 in
  • Coupling Mechanism: Bayonet Coupling
  • Interface Standards: CECC 22121, IEC 61169-8, MIL-STD-348B

BNC connector uses

The most common applications for BNC connectors are related to video and radio frequency functions, such as in test equipment, nuclear instrumentation, aerospace electronics (avionics), radio antennas and analog and serial digital interface video signals.

The BNC connector can be used as an alternative to the RCA connector for carrying composite video signals on commercial video devices. Consumer electronics built with RCA jacks can also often be used with BNC commercial video equipment by using an adapter.

Recording studios also use BNC connectors to synchronize various components of digital recording equipment via the transmission of word clock timing signals.

BNC assembly

There are multiple types of BNC connector assemblies depending on the application. This flexibility is another reason for this connector’s popularity.

BNC compression connector

A compression connector is a one-piece F connector. An F connector is a coaxial radio frequency connection used for satellite television and cable modems. They can be easily connected to the cable with a cable stripper and compression tool.

BNC crimp-on connector

Using a cable stripper and a compression tool, you can securely attach a BNC crimp-on connector to a coaxial cable. The crimp-on method is widely used and has 2-piece and 3-piece styles available.

BNC twist-on connector

Credit: Security Camera & Video Surveillance Blog, “What is the best BNC connector type?”

The twist-on BNC connector requires no tools to attach, only the cable. You can twist the connector onto the cable by hand.

BNC inserter/remover tool

A BNC inserter/remover tool is a lightweight, stainless steel tool used to apply torque for inserting or removing BNC connectors. They are designed to safely and quickly connect or disconnect BNC connectors in high-density, hard-to-reach areas without the risk of accidentally compromising or damaging adjacent connectors.

History of BNC connectors

BNC connectors were first developed in the late 1940s for the purpose of providing a high-quality connector capable of handling a wide variety of applications. It was named after its bayonet mount locking mechanism and its inventors, Paul Neill and Carl Concelman of the Amphenol Corporation. The close-fitting locking mechanism uses a mount similar to that of a bayonet knife attached to the end of rifles.

The correct name for this connector is the Bayonet Neill Concelman connector but is sometimes also referred to as a Berkeley Nucleonics Corporation connector, Bayonet Navy Connector, Baby N Connector, British Naval Connector and British National Connector. It was originally developed for the military but has since gained popularity for use in video and RF applications.

Neill and Concelman based the connector on the work of Octavio M. Salati of Hazeltine Electronics Corporation, who in 1945 invented a connector for coaxial cables that reduced wave reflection and loss. This was achieved by connecting across the radial surface of the cable instead of a terminated cross-section. Cross-sections experience signal degradation through reflection at a flat cable end. A patent for his invention was granted in 1951.

Paul Neill, an electrical engineer, also invented the N connector while working at Bell Labs. He set out to create a coaxial connector capable of handling microwave frequencies. His N connector was able to maintain characteristic impedance by minimizing the space between the center conductor connection and the outer shell to the feedline dimensions. The weatherproof structure had a female threaded outer shell that mated with matching male-threaded sockets. This type of connector is still used today.

Around the same time, Carl Concelman, another electrical engineer, invented the C connector while working at Amphenol. Concelman’s connector used the same methods of maintaining characteristic impedance as the N connector. However, he put a focus on ease-of-use, by using the bayonet quick-disconnect structure, rather than the screw and unscrew connection. The outer shell would be rotated to move the lugs into the short arm of the groove on the inner shell, The two connections would then be locked together.

Neill and Concelman then came together to develop a connector that shared the best characteristics of both their inventions, as well as the work of Salati. The BNC connector is essentially a miniature version of the N connector and C-type connectors, using the same approach to maintaining impedance and adopting the bayonet-style connection. The largest difference is that BNC connectors are smaller in size than both C and N types.

The BNC connector is widely used in electronics, although it is being superseded by the LEMO 00 mini-connector that handles higher densities. The HD-BNC connector and the DIN 1.0/2.3 also allow higher density in video broadcasting.

Versions of BNC connectors

All types of BNC connectors are commonly available in two categories: 50 ohm and 75 ohm

50 ohm and 75 ohm Connectors

An ohm is the unit of electrical resistance and is named after German physicist Georg Ohm. The difference in connection types between the 50 ohm and 75 ohm connectors is based on how they are attached to cables.

50 ohm is more widely used. It’s typically specified for frequencies up to 4 GHz and used for data transmission and RF.

75 ohm connectors are usually specified for use at frequencies up to 2 GHz. They can sometimes be recognized by the reduced absent dielectric in the mating ends. This type is primarily used in Video (particularly HD video signals) and DS3 Telco central office applications. Many VHF receivers use 75 ohm antenna inputs, and in turn, use 75 ohm BNC connectors.

There is a 95 ohm BNC connector, but it is rarely used and delegated for very specific applications. It’s virtually only used in aerospace applications, specifically to connect the glass cockpit displays on some aircraft.

50 ohm and 75 ohm connectors are able to mate with each other, and some BNC connectors have multiple ohm types. Connectors that comply with the 1978 standard, IEC 169-8, will mate non-destructively. At frequencies below 10 MHz, the impedance mismatch between a 50 ohm connector or cable and a 75 ohm one has negligible effects. But any frequency above 10 MHz can lead to signal reflections.

Types of connectors

There are a number of other BNC variant connectors that use a bayonet-type of connection. They all abide by the United States military standard MIL-PRF-39012 for entitled Connectors, Coaxial, Radio Frequency and General Specification.

Twin BNC or Twinax

Twin BNC (also known as twinax) connectors use two independent contact points, one male and one female. This allows the connection of a 75 ohm or 95 ohm shielded differential pair such as RG-108A. Twin BNC connectors have a lower frequency range and voltage, typically maxing out 100 MHz and 100 volts.

What that lack in frequency and voltage capabilities, they make up for in keyway polarization to ensure system integrity and prevent signals from being mixed. This makes them ideal for computer networking systems. They cannot mate with ordinary BNC connectors.

Triaxial connectors

Triaxial (or Triax) connectors were developed with reliability and longevity in mind. Their ability to carry a signal and guard is comparable to ground conductors. They are used in applications where maximum RF shielding and minimum noise radiation is required, such as in sensitive electronic measurement systems.

They include a three-lug arrangement to prevent accidental forced mating with a BNC connector. There are adaptors available that allow some interconnection possibilities between triaxial and BNC connectors.

Miniature connectors

Mini BNC and High-Density BNC (HD BNC) are smaller versions of BNC connectors. They can retain the electrical characteristics of the original BNC connectors but have smaller footprints and higher packing density on circuit boards and equipment backplanes.

Miniature BNC connectors have true 75 ohm impedance making them suitable for HD video applications. They are also commonly used in electronics but are being replaced by LEMO-00 miniature connectors.

SR connectors

Scientists in the USSR developed the SR connector for coaxial cables that was heavily based on the BNC connector. This is also called the CP conector. The difference lies in the dimensions of the connector to account for discrepancies in imperial to metric conversion.

High-voltage connectors

Standard BNC connectors typically max out at 500 volts. For anything higher, MHV (miniature high voltage) and SHV (safe high voltage) connectors are typically used instead. MHV connectors can be brute-forced to mate with BNC connectors but SHV connectors are a safer alternative that are unable to mate with BNC.

Reverse-polarity BNC connectors

There is also a variation on BNC connectors called reverse-polarity (RP-BNC), which are designed to reverse the polarity of the interface. This type swaps the female connector usually found in the jack into the plug, while the male connector is switched to the jack. An SHV connector uses the reverse polarity configuration.

Best BNC connector vendors

The BNC connector has been adopted across a wide variety of industries, far beyond its original intended use. As a result, there are many electronics companies that manufacture BNC connectors. These are some of the most popular:

  • Rconector
  • Smar

UPDATED: This article was updated on April 2, 2021 by Web Webster.