A BNC connector may look like a simple piece of hardware on the end of a coaxial cable, but in a professional SDI system it is part of the transmission path.
Professional digital video systems are designed around a 75-ohm characteristic impedance. That means the coaxial cable, connectors and other components in the signal path should be appropriate for 75-ohm video applications.
This becomes particularly important as systems move from HD and 3G-SDI to higher-bandwidth 6G-SDI and 12G-SDI.
So what exactly is a 75-ohm BNC connector, and why does it matter?
WHAT DOES 75 OHMS MEAN?
The 75-ohm specification refers to the characteristic impedance of the transmission system.
Professional video coaxial cable is engineered to maintain a nominal 75-ohm impedance along the signal path.
The goal is not simply to connect the center conductor and shield electrically. The cable and connectors work together as a controlled transmission system.
When the impedance changes significantly at a connector, adapter or other interface, some of the signal energy can be reflected rather than continuing cleanly through the path.
For digital video, maintaining a consistent signal path becomes increasingly important as bandwidth rises.
WHY DOES PROFESSIONAL VIDEO USE 75-OHM COAX?
75-ohm coaxial systems have long been used for video transmission and remain fundamental to professional SDI infrastructure.
Modern SDI BNC cable assemblies continue to use 75-ohm coaxial construction for connections between cameras, routers, switchers, monitors, recorders, converters and other professional video equipment.
When building an SDI path, the objective is to maintain appropriate transmission characteristics from the source output through the cable assembly to the receiving input.
50-OHM VS 75-OHM BNC: WHAT'S THE DIFFERENCE?
BNC connectors are used in more than one industry, and not every BNC application is professional video.
Two common impedance systems are 50 ohms and 75 ohms.
50-ohm systems
Commonly associated with RF, radio and certain test-and-measurement applications.
75-ohm systems
Commonly used for professional video, broadcast and SDI transmission.
The important point is that a connector should be selected for the transmission system it is intended to serve.
For professional SDI video, that means using components designed for a 75-ohm signal path.
CAN A 50-OHM BNC PHYSICALLY CONNECT TO A 75-OHM BNC?
Depending on the particular connector designs, BNC interfaces may appear mechanically compatible even when their electrical characteristics are intended for different impedance systems.
That can create a dangerous assumption:
If the connector fits, it must be correct.
Mechanical connection alone does not tell you whether the connector is appropriate for professional SDI transmission.
When specifying cable assemblies for video, the electrical performance of the complete assembly matters—not simply whether the connectors lock together.
WHY CONNECTOR IMPEDANCE MATTERS
A coaxial transmission path works best when its characteristic impedance remains controlled throughout the system.
A significant impedance discontinuity can create signal reflections and reduce the available transmission margin.
The effect may not always produce an immediate black screen.
A marginal system might instead experience:
- Intermittent video
- Signal dropouts
- Reduced reliable transmission distance
- Problems that appear only at higher SDI data rates
- A connection that works with one format but fails with another
If you're experiencing intermittent video, our SDI signal troubleshooting guide covers several other common causes.
WHY 12G-SDI MAKES CONNECTOR QUALITY MORE IMPORTANT
As SDI data rates increase, maintaining signal integrity becomes more demanding.
A cable assembly that successfully transports a lower-data-rate signal may have less transmission margin when used for 12G-SDI.
That means the complete assembly—including the coaxial cable, connectors and termination—should be appropriate for the required bandwidth.
When building a professional 4K system, choosing suitable cable while ignoring connector performance can undermine the purpose of selecting higher-performance coax in the first place.
Our 12G-SDI cable distance guide explains how cable construction and transmission distance affect 12G installations.
THE TERMINATION MATTERS TOO
Using the correct connector is only part of building a reliable cable assembly.
The connector also needs to be properly installed on the coaxial cable.
A professional termination needs to maintain the mechanical and electrical relationship between the cable and connector.
Potential termination problems can include:
- Improper cable preparation
- Incorrect connector selection for the cable
- Damage to the center conductor
- Shielding problems
- Loose mechanical termination
- Incorrect crimping
This is one reason professionally assembled and tested SDI cables can be valuable in production environments where signal reliability matters.
THE CONNECTOR MUST MATCH THE COAXIAL CABLE
BNC connectors are not simply divided into 50-ohm and 75-ohm versions.
The connector also needs to be designed for the physical dimensions and construction of the coaxial cable being terminated.
Mini RG59, standard RG59 and RG6-style professional video cables differ in physical size and construction.
That means the connector selected for one cable may not be appropriate for another.
For more information about cable sizes, see our Mini RG59 vs RG59 vs RG6 guide.
WHAT ABOUT HD-BNC?
Standard BNC is not the only 75-ohm coaxial connector used in professional video.
Modern high-density equipment frequently uses HD-BNC connectors.
HD-BNC provides a more compact interface that allows manufacturers to fit more video connections into limited panel space.
This can be particularly useful on routers, converters, multiviewers and other high-density professional equipment.
Although the physical connector is smaller, the same basic principle applies: the complete connection must be appropriate for the required professional video signal.
Read our HD-BNC vs BNC comparison for a closer look at the two connector formats.
WHAT ABOUT DIN 1.0/2.3?
DIN 1.0/2.3 is another compact coaxial connector format found on professional broadcast and video equipment.
Like HD-BNC, DIN connectors can help equipment manufacturers increase connection density when conventional BNC connectors would require more panel space.
Professional rack systems may therefore contain a mixture of BNC, HD-BNC and DIN 1.0/2.3 connections.
DOES EVERY BNC CABLE SUPPORT 12G-SDI?
No.
The presence of BNC connectors on both ends does not automatically make a cable assembly suitable for 12G-SDI.
Performance depends on the complete assembly, including:
- Coaxial cable construction
- Signal attenuation
- Cable length
- Connector performance
- Termination quality
- Connected equipment
A cable intended for lower-bandwidth video applications should not automatically be assumed to provide reliable 12G-SDI performance simply because it uses BNC connectors.
WHAT SHOULD YOU LOOK FOR IN AN SDI BNC CABLE?
75-ohm video construction
Use cable and connectors intended for professional video transmission.
Correct SDI bandwidth
Select an assembly appropriate for the 3G, 6G or 12G signal being transported.
Appropriate cable size
Balance Mini RG59, RG59 or RG6 construction against the required distance and installation environment.
Correct connector for the cable
The connector should be designed for the specific coaxial cable construction.
Professional termination
Proper assembly helps maintain mechanical reliability and signal-path performance.
Appropriate cable length
Avoid treating every SDI cable as though transmission distance does not matter.
DON'T TROUBLESHOOT ONLY THE CABLE
If an SDI system is unreliable, inspect the complete transmission path.
A professional signal may travel through a cable, patch panel, router, adapter, second cable and finally into a monitor or switcher.
Every interface becomes part of the path.
Testing with a short known-good cable directly between the source and destination is often an effective way to determine whether the problem is related to cabling or another piece of equipment.
75 OHMS IS PART OF THE COMPLETE SDI SYSTEM
The important takeaway is that a BNC connector should not be treated as a generic electrical plug.
In professional SDI video, it is part of a controlled 75-ohm transmission path.
As video systems move toward higher-bandwidth 6G and 12G-SDI signals, selecting the appropriate coaxial cable, connector and termination becomes increasingly important.
A reliable SDI cable assembly is therefore the combination of the correct coax, correct connector, correct termination and appropriate cable length.
PROFESSIONAL 75-OHM SDI CABLE ASSEMBLIES
AV-Cables manufactures professional SDI BNC cable assemblies for broadcast, video production, studios, live events, houses of worship, corporate AV, government, OEM and systems integration applications.
Available configurations include Mini RG59, RG59 and RG6 coaxial assemblies, HD-BNC cables, DIN 1.0/2.3 cables and multi-channel SDI snake assemblies.
AV-Cables professional cable assemblies are hand assembled in the USA and individually tested before shipment.
NEED HELP CHOOSING AN SDI CABLE?
Tell us the equipment, SDI format, connector type and required cable distance. AV-Cables can help identify the appropriate professional cable assembly for your signal path.
AV-Cables — Professional Broadcast Connectivity Solutions