A BNC cable is a finished coaxial cable assembly fitted with one or more BNC connectors. Choosing a suitable assembly requires checking the equipment port, 50 or 75 ohm impedance, coaxial cable type, cable length, signal requirement, and connector termination together. A cable for a 50 ohm RF test path is not the same as a 75 ohm video cable, even when both assemblies use a similar bayonet interface.
What Is a BNC Cable
A BNC cable refers to a coaxial cable assembly that uses BNC (Bayonet Neill Concelman) connectors to carry RF or video signals. In most practical contexts, it describes a finished cable assembly rather than a standalone cable type. The performance of a BNC cable therefore depends on both the BNC connector interface and the coaxial cable used between the connectors.
BNC cables are commonly used in RF signal paths and video transmission systems where stable impedance, shielding effectiveness, and repeatable connections are required. The bayonet style coupling allows the connector to be locked and released quickly, making BNC cables suitable for test environments, broadcast equipment, and video monitoring installations where connections may need to be changed or verified regularly.
The term BNC identifies the connector interface, but it does not define the complete cable specification. Two assemblies may both be described as BNC cables while using different impedance values, cable diameters, shielding structures, connector orientations, and termination methods.
How to Choose a BNC Cable
Begin with the connected equipment. Confirm the port type, signal impedance, operating frequency or video format, cable routing space, and required cable length. The connector at each end then needs to match the port gender, cable construction, and available installation space.
The table below gives a general starting point. Equipment documentation and the cable assembly specification remain the final references.
| Application | Typical Impedance | Typical Cable Options | Main Items to Confirm |
|---|---|---|---|
| RF test and measurement | Usually 50 ohm; verify the instrument input | RG58, RG174, RG316, or a qualified 50 ohm test cable | Instrument input, termination, frequency, loss, and flexibility |
| Radio and instrumentation links | 50 ohm | RG58 or a lower loss 50 ohm cable | Frequency, cable length, signal level, and environment |
| CCTV and analog video | 75 ohm | RG59, RG6, or specified video coax | Camera and recorder ports, distance, shielding, and routing |
| Broadcast and digital video | 75 ohm | Qualified 75 ohm broadcast cable | Video format, cable length, return loss, and connector rating |
What Makes a BNC Cable Assembly Compatible
A compatible assembly combines four matched elements: the equipment interface, BNC connector version, coaxial cable, and termination structure. The front bayonet interface confirms how the connector mates, while the rear body determines which cable dimensions and construction it can accept.
At the cable end, the center contact, dielectric support, cable entry, ferrule, shield connection, and strain relief need to match the selected coaxial cable. A BNC connector made for RG58 cannot be assumed to fit RG59, RG6, RG174, or RG316.
Cable outer diameter alone is not enough to confirm compatibility. Center conductor diameter, dielectric diameter, conductor construction, shield type, jacket thickness, and cable preparation dimensions also affect the connector selection.
50 Ohm vs 75 Ohm BNC Cables
BNC cables are commonly categorized by characteristic impedance. The two most widely used versions are 50 ohm and 75 ohm. Although they use the same BNC coupling family, their internal geometry, cable construction, and typical applications differ. Selecting the impedance specified by the connected equipment helps limit signal reflections and performance loss.
50 Ohm BNC Cables
A 50 ohm BNC cable is commonly selected for RF test equipment, radio communication links, instrumentation, signal generators, analyzers, and other 50 ohm signal paths. Common cable choices include RG58 for general connections and RG174 or RG316 when a smaller cable diameter or more flexible routing is required.
The equipment port, cable, BNC connector, adaptor, and termination need to follow the same impedance requirement. For instruments with selectable input impedance or external termination, check the test setup before confirming the cable assembly.
75 Ohm BNC Cables
A 75 ohm BNC cable is commonly selected for CCTV, analog video, broadcast equipment, video distribution, and digital video links. RG59 and RG6 are common cable families, although the selected cable still needs to meet the required video format, transmission distance, and equipment specification.
Digital video applications may require a specified 75 ohm broadcast cable and a connector version rated for the required signal format. A general BNC interface does not confirm that the complete assembly is suitable for every SDI link.
Many standard 50 ohm and 75 ohm BNC interfaces can lock together mechanically. Mechanical mating does not confirm an impedance matched signal path. Mixing a 50 ohm connector or cable into a 75 ohm path, or the reverse, can increase reflections and affect measurement or video performance.
For a more detailed explanation of why 50 Ω and 75 Ω impedance standards exist and how they affect signal performance in RF and video systems, refer to the article Understanding 50Ω vs 75Ω Impedance.
Does BNC Cable Length and Frequency Affect the Choice
There is no single maximum cable length that applies to every BNC connection. The usable length depends on the coaxial cable, operating frequency or video format, and how much signal loss the connected equipment can tolerate.
As the cable run becomes longer or the operating frequency increases, attenuation becomes more important. A small flexible cable may work well for a short connection, while a longer RF path may require a lower-loss 50 ohm cable. For a 75 ohm video link, the cable also needs to meet the required video format and transmission distance.
Do not choose a BNC cable from length alone. Compare cable attenuation at the required frequency, finished assembly length, connector performance, and the allowable insertion-loss or return-loss target together.
Choose a BNC Cable by Application
Video Surveillance and Security Systems
For CCTV and analog video, start with a 75 ohm signal path and confirm that the camera, recorder, cable, adaptor, and termination follow the same impedance. RG59 is common for many shorter video links, while RG6 or another 75 ohm cable may be used when the route, attenuation requirement, or installation structure calls for a different cable.
Test and Measurement Equipment
For test and measurement equipment, do not assume that every BNC input is always 50 ohm. Some oscilloscope inputs use a high input impedance unless a 50 ohm input or external termination is selected, while many signal generators and RF instruments use a controlled 50 ohm path. Confirm the instrument setting first, then compare cable length, loss, and flexibility.
Broadcast and Digital Video
For broadcast and digital video, use a 75 ohm cable and connector combination that meets the required video format and transmission distance. A cable that works for analog CCTV is not automatically suitable for every SDI link, so check the cable model, connector rating, finished length, and required return-loss performance before confirming the assembly.
BNC Termination Types: Crimp, Solder, and Clamp
Crimp BNC connectors are commonly selected for repeatable cable assembly production. The center contact, ferrule, cable preparation dimensions, and crimp tooling need to match the selected cable and connector.
Solder termination may be used when the connector structure requires the center conductor, shield, or both parts to be soldered. The soldering process needs to avoid dielectric deformation, loose braid strands, excessive exposed conductor, and uneven shield contact.
Clamp versions are available for selected cable constructions and may be useful when the connector is designed for mechanical cable retention without a standard crimp ferrule. Connector drawings define which attachment method applies.
No termination method is suitable for every BNC cable. Assembly quantity, cable construction, connector design, service requirements, tooling, and inspection method all influence the decision. Our comparison of crimp and solder RF connector termination explains these process differences in more detail.
If a BNC cable works normally when stationary but loses the signal when the connector or cable entry moves, see our guide to troubleshooting an intermittent BNC cable.
For a step-by-step selection process based on the connected equipment, see our guide to choosing BNC connectors for video and test systems.
FAQ
Conclusion
Choosing a BNC cable starts with the equipment interface and system impedance, followed by the cable type, length, signal requirement, connector structure, and termination method. A 50 ohm RF test cable and a 75 ohm video cable can use similar BNC interfaces while requiring different cable and connector parts. For a custom BNC cable assembly, share the port details, connector configuration, cable model, finished length, frequency or video format, and test requirements with the Bafitop team for review.