An SDI cable can pass a basic continuity test and still fail in a professional video system.

That distinction becomes increasingly important with higher-bandwidth signals such as 6G-SDI and 12G-SDI.

A continuity tester can identify important wiring faults such as an open conductor or short circuit, but successful SDI transmission depends on much more than electrical continuity.

If you are troubleshooting a questionable SDI BNC cable, understanding the difference between continuity testing and signal-performance testing can save considerable troubleshooting time.

WHAT DOES A BASIC BNC CONTINUITY TEST CHECK?

A coaxial SDI cable contains a center conductor surrounded by dielectric material, shielding and an outer jacket.

A basic electrical test can verify several fundamental conditions.

• Center conductor continuity from one end to the other
• Shield continuity from one end to the other
• No short between the center conductor and shield

If the center conductor is open, the shield is disconnected or the center conductor is shorted to the shield, the cable clearly has a problem.

Continuity testing is therefore a useful first step—but it does not tell the entire story.

WHY A CONTINUITY TEST DOESN'T PROVE SDI PERFORMANCE

Continuity testing answers a basic question:

Is there an electrical connection between the two ends?

SDI testing asks a much more demanding question:

Can this complete cable assembly reliably transport a high-frequency digital video signal?

A simple tester does not fully evaluate characteristics such as:

• High-frequency attenuation
• Return loss
• Impedance consistency
• Connector performance
• Termination quality at SDI frequencies
• Available transmission margin

This is why a cable should not automatically be considered suitable for 12G-SDI simply because a multimeter or continuity tester indicates that the conductors are connected.

A CABLE CAN BE ELECTRICALLY CONNECTED AND STILL BE MARGINAL

Consider a cable with a damaged termination.

The center conductor may still make electrical contact from end to end, so a continuity test passes.

But if the connector, cable geometry or termination has been compromised, the cable may introduce an impedance discontinuity or other degradation that affects high-frequency performance.

The result could be a cable that:

• Passes continuity
• Works with HD-SDI
• Works with 3G-SDI
• Becomes intermittent at 6G-SDI
• Fails at 12G-SDI

That behavior is an important troubleshooting clue.

WHY 12G-SDI EXPOSES MARGINAL CABLES

As SDI data rates increase, the demands placed on the transmission path increase as well.

A cable assembly with adequate margin for a lower-bandwidth format may have substantially less margin when transporting 12G-SDI.

This helps explain why an existing cable can appear perfectly functional until cameras, routers, switchers or monitors are upgraded to a higher-bandwidth UHD workflow.

The cable didn't necessarily suddenly lose electrical continuity. The system may simply be asking it to transport a more demanding signal.

For more background, read 3G-SDI vs 6G-SDI vs 12G-SDI: What's the Difference?

STEP 1: INSPECT THE SDI CABLE

Before connecting test equipment, perform a visual and mechanical inspection.

Look for:

• Damaged BNC connectors
• Bent or damaged center contacts
• Loose connector bodies
• Damaged bayonet locking features
• Severe cable kinks
• Crushed sections of coax
• Cuts or abrasion in the jacket
• Damage where the cable enters the connector

Also gently check the termination area. A connector that moves independently of the cable or produces intermittent video when flexed deserves further investigation.

STEP 2: CHECK CENTER-CONDUCTOR CONTINUITY

With the cable disconnected from equipment, a continuity tester or multimeter can be used to check the center conductor from one connector to the other.

The objective is to confirm that the center conductor provides an uninterrupted electrical path through the assembly.

An open center conductor indicates a failed cable or termination.

STEP 3: CHECK SHIELD CONTINUITY

The outer conductive portions of the BNC connectors should also maintain continuity through the cable's shielding system.

An open shield can indicate cable damage or a termination problem.

Both the center conductor and shield are necessary parts of the coaxial transmission system.

STEP 4: CHECK FOR A CENTER-TO-SHIELD SHORT

The center conductor should not be electrically shorted to the shield.

Checking between the BNC center contact and outer conductor can identify a direct short caused by cable damage, incorrect preparation or termination problems.

If a cable has either an open conductor or a direct short, there is little reason to continue SDI troubleshooting with that assembly.

STEP 5: SUBSTITUTE A KNOWN-GOOD SDI CABLE

One of the most useful field troubleshooting techniques requires no specialized laboratory equipment.

Replace the questionable cable with a known-good SDI cable of appropriate specification.

If the video problem disappears, the original cable becomes a strong suspect.

For the cleanest test, temporarily simplify the signal path:

Source → Known-Good Cable → Destination

This can help eliminate patch panels, adapters, routers and other intermediate components as possible causes.

Our SDI signal troubleshooting guide explains this process in more detail.

STEP 6: TEST AT THE ACTUAL SDI DATA RATE

If the system is intended to operate at 12G-SDI, testing only with a lower-bandwidth format does not prove that the cable will reliably transport the required 12G signal.

When possible, evaluate the cable under the conditions in which it will actually be used.

A useful troubleshooting comparison can be:

If reliability decreases as the data rate increases, investigate the cable type, cable length, connectors and termination.

STEP 7: CONSIDER THE CABLE LENGTH

Testing cannot be separated from transmission distance.

A particular cable construction may provide adequate performance at one length but insufficient transmission margin at a substantially longer length.

Mini RG59, RG59 and RG6-style professional video coax have different physical and transmission characteristics.

Our Mini RG59 vs RG59 vs RG6 comparison explains how these cable constructions fit different applications.

For 12G systems, also see How Far Can You Run 12G-SDI?

THE BNC CONNECTOR IS PART OF THE TEST

An SDI cable assembly is not simply a length of coax.

The connectors and terminations are part of the transmission path.

Professional SDI systems use 75-ohm video connectivity, and connector performance becomes increasingly important as bandwidth increases.

A poor termination can therefore create problems even when the coaxial cable itself is undamaged.

This is also why simply replacing a connector with any physically compatible BNC is not necessarily the correct repair.

WHAT ABOUT HD-BNC AND DIN 1.0/2.3 CABLES?

The same troubleshooting principles apply when professional equipment uses compact connectors.

High-density routers, converters and other broadcast equipment may use HD-BNC or DIN 1.0/2.3 connections.

When troubleshooting, inspect and test the complete assembly rather than assuming the compact connector or adapter cannot be the source of the problem.

FIELD TESTING VS PROFESSIONAL SIGNAL TESTING

Basic field troubleshooting and professional signal-performance testing serve different purposes.

The key distinction is simple: electrical continuity and high-frequency transmission performance are not the same test.

A PRACTICAL SDI CABLE TESTING CHECKLIST

1. Inspect the cable and connectors.
2. Check center-conductor continuity.
3. Check shield continuity.
4. Check for a center-to-shield short.
5. Substitute a known-good cable.
6. Simplify the signal path.
7. Test using the actual required SDI format.
8. Consider cable length and cable construction.
9. Inspect every adapter and intermediate connection.

This process can quickly separate obvious wiring failures from higher-frequency performance problems that require further investigation.

WHY TESTING MATTERS IN PROFESSIONAL VIDEO

Intermittent cables are particularly disruptive in live production because a marginal connection may appear normal during setup and fail once the system is in use.

Broadcast facilities, production companies, fly packs and mobile systems may also contain dozens or hundreds of coaxial connections.

Using appropriately specified, properly terminated and tested cable assemblies helps reduce uncertainty when troubleshooting the larger video system.

PROFESSIONAL SDI CABLE ASSEMBLIES FROM AV-CABLES

AV-Cables manufactures professional SDI cable assemblies for broadcast facilities, video production, live events, studios, houses of worship, corporate AV, government, OEM and systems integration applications.

Available solutions include Mini RG59, RG59 and RG6 SDI assemblies, HD-BNC cables, DIN 1.0/2.3 cables and multi-channel SDI snake cables.

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

AV-Cables — Professional Broadcast Connectivity Solutions