BNC Connector: Complete Guide to Bayonet Coaxial Connectors

Key Takeaways

BNC connectors are bayonet-style coaxial connectors with 50-ohm or 75-ohm impedance, featuring a quarter-turn locking mechanism.
They operate from DC to about 4 GHz and are widely used in test equipment, video applications, and radio frequency (RF) systems.
BNC stands for Bayonet Neill-Concelman, named after inventors Paul Neill and Carl Concelman.
Available in both 50-ohm (RF) and 75-ohm (video) versions.
Typically rated for up to 500 mating cycles with proper installation and maintenance.

What is a BNC Connector

A BNC connector is a compact, quick-connect radio frequency connector designed for coaxial cables. The acronym “BNC” stands for Bayonet Neill-Concelman, after inventors Paul Neill and Carl Concelman, who developed the design in the 1940s.

The key feature is the bayonet coupling mechanism, which allows secure connection with a quarter-turn twist instead of a threaded interface. This makes it more convenient in applications requiring frequent connecting and disconnecting.

BNC connectors are available in 50-ohm and 75-ohm variants, optimized for RF systems and video transmission respectively. Impedance matching is crucial to avoid signal reflections and maintain signal quality.

When compared with SMA connectors, which use external threads for microwave systems above 4 GHz, BNC connectors provide better performance within their intended frequency range while offering faster handling.

Most versions are manufactured with a brass body, nickel or gold plating, and sometimes stainless steel for light weight or outdoor applications.

Technical Specifications

Impedance Characteristics

50-ohm BNC: common in test equipment, antennas, and RF devices.
75-ohm BNC: used in broadcasting, CCTV, and professional video systems.

The difference lies in the inner diameter of the dielectric and center pin tolerances.

Frequency Performance

Standard BNC: DC to ~4 GHz.
High-performance BNC: up to 11 GHz (some up to 18 GHz).
VSWR: typically < 1.3:1.
Insertion loss: minimal (<0.1 dB).

Environmental and Mechanical

Temperature range: -65°C to +165°C.
Voltage withstand: up to 1500 VRMS.
Mating durability: approx. 500 cycles.
Shielding: > 90 dB, protecting against electromagnetic interference.

Collection of BNC connectors in 50 ohm and 75 ohm versions with gold and nickel plating

Types and Variants

Standard Configurations

Male connector: center pin, found on cables and outputs.
Female connector: recessed contact, common for equipment inputs.
Available as straight or right-angle plugs for tight spaces.

Panel and Bulkhead Mounting

Bulkhead connectors use a hex nut for chassis mounting. Some offer DC isolation between shell and chassis to prevent interference.

Specialized Variants

High-frequency BNC: supports >11 GHz.
Reverse polarity BNC: reversed contacts for regulatory compliance.
Twinax BNC: dual contacts for 78Ω or 95Ω differential signals.
Subminiature version: compact, light weight, up to 2–3 GHz.

Applications and Use Cases

Test and Measurement

Oscilloscopes, signal generators, and analyzers rely on BNC plugs for excellent electrical performance. Their quick-connect design is ideal where many coaxial cables must be swapped.

Video and Broadcasting

75-ohm connectors are the industry standard in CCTV, SDI broadcasting, and professional video. They ensure reliable, low loss signal transmission.

Professional video broadcasting equipment with cameras using 75 ohm BNC connectors

RF and Communication

Amateur radios, antennas, and RF systems commonly use 50-ohm BNC. They are commonly used in portable devices due to their compact size.

Laboratory and Scientific

Instruments across disciplines use BNC for flexible setups. High quality cables with proper outer conductor termination ensure accurate results.

Installation and Proper Usage

Cable Preparation

For flexible coaxial cable such as RG-58 or RG-59, strip the jacket precisely. Ensure correct outer conductor and dielectric exposure for stable impedance.

Quarter-Turn Locking

Align the pins, insert, and twist 90° until secure. Avoid over-torqueing.

Maintenance

Inspect for bent contacts or damage.
Clean gently; avoid harsh solvents.
Protect with dust caps when unused.

BNC connector installation diagram with outer conductor, dielectric, and crimp assembly

Compatibility and Standards

Standardized under IEC 61169-8, MIL-STD-348, and MIL-C-39012.
Ensures interoperability between different manufacturers.

Cable Compatibility

RG-58 (50 ohm, RF).
RG-59 (75 ohm, video).
Low loss variants preferred at higher frequency.

Adapters

BNC–SMA, BNC–N-type adapters expand use across devices.
Each extra interface introduces potential loss.

Advantages and Limitations

Advantages

Fast quarter-turn connection.
Outstanding mechanical durability when installed properly.
Widely standardized and available.
Secure coupling, resists accidental disconnection.

Limitations

Frequency limited compared with SMA in microwave systems.
Larger than miniature connectors.
Not designed for high-power RF.

Comparison of coaxial connectors: BNC vs SMA vs N connector types

Frequently Asked Questions

What does BNC stand for?
Bayonet Neill-Concelman, after its inventors.

Can I mix 50-ohm and 75-ohm connectors?
No, mismatching causes reflections and degraded signals.

How many mating cycles are possible?
Typically 500+, depending on quality and use.

Difference between BNC and TNC?
TNC uses a threaded interface, offering better sealing for outdoor applications.

Are BNC waterproof?
Standard versions are not. For outdoor applications, use weatherproofed BNC or sealing accessories.