Can you connect two SDI cables together?

Yes. Two professional SDI cables can be joined using an appropriate 75-ohm BNC female-to-female coupler.

That can be extremely useful when a cable is slightly too short, when extending a temporary production run or when troubleshooting a professional video system.

But joining two cables is not exactly the same as using one continuous cable.

The coupler creates another connection in the SDI signal path, and at higher data rates such as 6G-SDI and 12G-SDI, maintaining a properly designed 75-ohm transmission path becomes increasingly important.

Here's what you should know before using a BNC coupler to extend an SDI cable.

YES — BUT USE A TRUE 75-OHM BNC COUPLER

SDI video systems use a nominal 75-ohm coaxial transmission path.

If two SDI cables need to be joined, the coupler between them should also be intended for 75-ohm video applications.

A female-to-female BNC coupler—sometimes called a BNC barrel—allows the male BNC connector on one cable to connect directly to the male BNC connector on another.

The basic signal path becomes:

The coupler does not convert or amplify the video signal. It simply provides a physical connection between the two coaxial assemblies.

WHY 75 OHMS MATTERS

Professional SDI equipment, coaxial cable and connectors are designed around a 75-ohm transmission system.

Maintaining consistent impedance throughout the signal path helps preserve signal integrity.

This is why professional SDI assemblies should use true 75-ohm BNC connectors rather than simply using any connector that happens to fit.

DOES A BNC COUPLER CAUSE SIGNAL LOSS?

Every real-world component added to a high-frequency signal path introduces some electrical effect.

That includes connectors, couplers, patch panels and other connection points.

A properly designed 75-ohm coupler can be useful in a professional system, but adding connections does not improve the signal.

This is one reason a single correctly sized cable is generally preferable when designing a permanent installation.

Think of the coupler as another part of the total transmission path rather than as a way to reset the allowable cable distance.

CABLE LENGTHS ARE CUMULATIVE

This is one of the most important points when extending an SDI cable.

If you connect a 50-foot cable to another 50-foot cable, you have effectively created a signal path approximately 100 feet long—plus the additional connection between them.

You do not get the transmission capability of two independent 50-foot runs.

Always evaluate the entire signal path when determining whether the cable construction is appropriate for the SDI format and distance.

WHAT ABOUT 12G-SDI?

12G-SDI places greater demands on the coaxial transmission path than lower-rate SDI formats.

That makes cable selection, connectors, termination quality and total distance especially important.

If you're extending a 12G-SDI connection, don't assume that a coupler automatically makes any two cables suitable for the application.

Consider:

• The specific coaxial cable construction
• The total combined cable length
• The quality of both cable assemblies
• The BNC connectors
• The coupler
• Any additional patch points in the path

For critical permanent 12G-SDI connections, using one appropriately sized 12G-SDI cable assembly is generally the cleaner approach.

WHEN A BNC COUPLER MAKES SENSE

A coupler can be extremely useful in situations such as:

• Temporary live productions
• Extending a cable that is just short of the destination
• Testing and troubleshooting
• Emergency production changes
• Connecting existing cable runs
• Portable fly-pack systems
• Field production

For example, discovering during setup that a 25-foot cable needs another 10 feet does not necessarily require abandoning the original cable. An appropriate coupler and additional cable can provide a practical solution if the complete signal path remains within the system's operating requirements.

WHEN SHOULD YOU USE ONE LONGER CABLE INSTEAD?

For a permanent installation, one continuous cable is usually preferable when practical.

Using the correct length from the beginning provides several advantages:

• Fewer connection points
• Fewer components to troubleshoot
• Cleaner cable management
• Less chance of an intermediate connection being accidentally disconnected
• A simpler signal path

If a rack permanently requires a 40-foot cable, repeatedly connecting two 20-foot assemblies may not be the best long-term design simply because those cables happen to be available.

CAN YOU CONNECT DIFFERENT SDI CABLE TYPES?

Physically, two 75-ohm BNC cable assemblies with compatible connectors can be joined with an appropriate coupler.

But the complete path is still limited by the characteristics of the components used.

For example, connecting a larger RG6 cable to Mini RG59 does not make the Mini RG59 portion perform like RG6.

Likewise, attaching a cable intended for a lower-bandwidth application to a 12G-capable assembly does not automatically make the entire path suitable for 12G-SDI.

The complete signal path is only as capable as the components used throughout it.

BNC COUPLER VS BNC EXTENSION CABLE

There is another way to extend a BNC connection.

Instead of using two standard male-to-male cables with a female-to-female coupler, a purpose-built BNC male-to-female extension cable can provide the additional distance while eliminating the separate barrel between the two cable assemblies.

This can be useful when extensions are a regular part of the production workflow.

The same rules still apply: the coaxial construction, connectors, total distance and required SDI data rate must be considered as a complete system.

DON'T CREATE A CHAIN OF COUPLERS

One coupler can solve a practical production problem.

A long chain of short cables and adapters is another matter.

If a run starts looking like this:

it's worth replacing the collection of components with a correctly sized assembly.

Reducing unnecessary connections makes the system easier to install, troubleshoot and maintain.

CHECK THE COUPLER WHEN TROUBLESHOOTING

If an SDI signal becomes intermittent after adding an extension, don't immediately assume the cable itself has failed.

Inspect every new connection in the path.

Check that:

• Both BNC connectors are fully locked
• The coupler is appropriate for the application
• Connectors are not damaged
• Cables are not sharply bent near the connection
• The total run isn't exceeding the practical capability of the cable system

If removing the extension restores reliable video, the additional cable length or added connection is an important troubleshooting clue.

SDI EXTENSION CHECKLIST

THE BOTTOM LINE

Yes, you can connect two SDI cables together using an appropriate 75-ohm BNC female-to-female coupler.

It's a useful solution for temporary extensions, live production, troubleshooting and situations where an existing cable is simply a little too short.

Just remember that the two cables become one longer transmission path.

For permanent installations—especially demanding 12G-SDI paths—one correctly sized cable assembly is generally preferable to adding unnecessary connection points.

RIGHT CABLE + RIGHT CONNECTORS + RIGHT DISTANCE

PROFESSIONAL 75-OHM BNC SOLUTIONS

AV-Cables manufactures professional SDI and BNC cable assemblies for broadcast, video production, studios, mobile trucks, fly packs and professional AV systems.

Available solutions include Mini RG59, RG59, RG6, 6G-SDI, 12G-SDI, BNC extension cables and professional 75-ohm BNC connectivity.

AV-Cables cable assemblies are hand assembled in the USA and individually tested before shipment.

AV-Cables — Professional • Reliable • Connected