An SDI cable is not selected by resolution alone. The right choice depends on the serial data rate, required run length, cable attenuation, connector transitions, installation method, and the transmitter and receiver at each end. A short 12G-SDI patch lead and a long fixed 12G-SDI run place very different demands on the assembly, even if both carry a 4K signal.
For broadcast engineers, systems integrators, and equipment buyers, the practical goal is to preserve a reliable 75-ohm path from source to destination. This guide explains what the 3G, 6G, and 12G labels mean, how to compare cable options, and which details to put in a purchase specification.
What do 3G, 6G, and 12G-SDI mean?
The number in an SDI label refers to the nominal serial data-rate class. It is not a cable model or a guaranteed maximum cable length. Common HD and UHD SDI interfaces include 1.5G HD-SDI, 3G-SDI, 6G-SDI, and 12G-SDI. In the commonly used SMPTE mappings, 3G-SDI carries approximately 2.97 Gb/s, 6G-SDI approximately 5.94 Gb/s, and 12G-SDI approximately 11.88 Gb/s. A 12G-SDI single-link interface is used for formats such as 4K/UHD at 60 frames per second when the equipment and signal format support it.
| SDI class | Approximate serial rate | Typical context | Cable-selection implication |
|---|---|---|---|
| 1.5G HD-SDI | 1.485 Gb/s | HD video workflows | Lower-frequency loss requirements than 3G or UHD links, but length and receiver limits still apply |
| 3G-SDI | 2.97 Gb/s | 1080p workflows and some 2K formats | Verify cable suitability at the relevant frequency and total installed length |
| 6G-SDI | 5.94 Gb/s | Some 4K/UHD workflows, commonly up to 30p | Requires lower loss and suitable interconnect performance than lower-rate links |
| 12G-SDI | 11.88 Gb/s | Single-link 4K/UHD workflows, commonly up to 60p | Most demanding of these examples; cable, connectors, and transitions need explicit 12G suitability |
These descriptions are practical orientation, not a substitute for the interface standard or equipment manual. Frame rate, bit depth, chroma sampling, mapping, and the specific SMPTE interface determine the actual signal format. Confirm those details with the system design before choosing a cable.
Start with the complete signal path
A cable datasheet may report attenuation per unit length at a given frequency. The receiver sees more than the bulk cable: both connector terminations, any patch panel or barrel adapter, equipment input and output, and any cable transitions contribute to the link. The available margin also depends on the source output and receiver equalization. Therefore, a generic distance claim such as “supports 12G to 100 m” should not be applied to every cable or installation.
For an initial review, gather:
- The exact SDI interface and video format, including the data-rate class.
- One-way route length, including service loops and patch leads.
- Cable manufacturer and part number, or minimum electrical requirements if substitutions are allowed.
- Connector types and every inline transition, patch panel, or adapter.
- Whether the cable is fixed, repeatedly handled, or flexed during operation.
- The source and receiver models and the acceptance method required by the project.
Use the equipment and cable manufacturers’ distance charts for the exact combination, then confirm the assembled path under the intended operating conditions. Where link margin is critical, system testing is more meaningful than inferring performance from a nominal cable category.
Compare cable construction, not just the SDI label
75-ohm characteristic impedance is the normal requirement for broadcast SDI coaxial paths. However, 75 ohms alone does not establish that a cable is suitable for a particular data rate or length. Conductor size, dielectric construction, shielding, attenuation, return loss, and connector termination all affect the result.
A larger coaxial cable often has lower attenuation over a given length, but it takes more space, weighs more, and may be harder to route through dense racks or small camera connections. A thinner cable can improve flexibility and packing density, while its higher loss may reduce the useful run length. Neither “thick” nor “low loss” is sufficient as a standalone specification; compare published attenuation at the relevant frequencies and include the mechanical constraints.
Shielding also has two roles: it helps control electromagnetic coupling and forms the outer conductor of the coaxial transmission line. Foil and braid constructions differ in coverage, flexibility, and handling behavior. The chosen construction should match the electrical requirements and the installation environment rather than being selected by a generic “double shield” label.
For example, Canare publishes a 75-ohm 12G-SDI cable table with attenuation figures at 6 GHz and product-specific transmission-distance guidance; its catalog shows different attenuation values for different cable sizes. Belden likewise identifies specific 4K UHD cable models for 12G-SDI and lists applicable SDI standards. These are examples of why the exact part number and manufacturer data matter; they are not interchangeable guarantees for other cable families.
Choose a cable type for the installation
Fixed rack, studio, or facility routes
For permanent installation, specify the exact cable model, route length, jacket and building rating required by the project, bend radius, and termination method. Confirm whether the path uses standard BNC, miniature BNC, or another interface, especially in high-density equipment where connector size can affect panel layout and service access.
Some cable models are designed for fixed installation and others for mobile use. Confirm this distinction in the supplier’s datasheet. A cable that performs electrically on a bench may not tolerate repeated coiling, flexing, or handling if it was designed for permanent routing.
Mobile production and camera links
Mobile camera cables are handled, bent, coiled, and moved more often than fixed infrastructure cable. Prioritize the manufacturer’s stated mobile-use construction, flexibility, bend guidance, and compatible connector system. Add strain relief and abrasion protection if the route exposes the assembly to repeated handling. Avoid specifying a fixed-installation cable solely because its attenuation or outside diameter appears attractive.
Dense patching and miniature connectors
Micro BNC and similar compact interfaces can increase port density, but they require connector and cable compatibility. The mating connector needs to match the equipment interface and the selected cable termination system. Check connector impedance, supported SDI rate, cable preparation dimensions, and any tool or strain-relief requirements. A miniature connector’s ability to physically mate does not prove that the complete link meets its required performance.
Why connectors and transitions matter
SDI coax assemblies should preserve the intended 75-ohm interface through the cable and its terminations. BNC is available in both 50-ohm and 75-ohm variants; similar appearance is not evidence of electrical compatibility. Specify 75-ohm BNC where the equipment calls for it, and identify the exact connector series or approved part number when the project requires controlled performance.
Every barrel, coupler, patch panel, and adapter adds another interface. Keep the path simple where practical, and include all transitions when evaluating the link budget. For high data rates, connector installation quality matters as well: the termination must match the cable construction and follow the connector manufacturer’s preparation and crimp instructions. Continuity testing can detect opens and shorts, but it does not demonstrate that an assembly meets an SDI loss or return-loss requirement.
A practical SDI cable comparison checklist
| Requirement | What to verify | Why it matters |
|---|---|---|
| Impedance | 75-ohm cable and matching 75-ohm interfaces | Reduces impedance discontinuities in the video path |
| Data-rate class | Suitability for the specified 1.5G, 3G, 6G, or 12G link | Rate class alone does not define a usable length |
| Attenuation | Manufacturer data at relevant frequencies and the planned length | Helps assess receiver margin across the route |
| Return loss / interface performance | Cable and connector data where specified by the project | Discontinuities can degrade signal integrity |
| Length | Finished route plus patch leads, service loops, and transitions | Total path differs from the wall or tray measurement |
| Mechanical duty | Fixed, mobile, flexing, or repeated-coiling use | Construction and jacket need to suit handling conditions |
| Connector | Exact type, impedance, gender, orientation, and equipment match | Mating fit does not establish electrical suitability |
| Verification | Continuity, visual inspection, and any required RF or system test | Test evidence should match the application risk |
What to include in an SDI cable RFQ
A useful request for quotation lets a supplier assess both the electrical path and the finished assembly. Include:
- SDI standard or interface class and the intended video format.
- Required cable manufacturer and part number, or approved electrical and mechanical limits.
- Cable length, tolerance, and the measurement reference points.
- Connector part numbers at both ends, including gender, orientation, and any miniature interface.
- Total route length and a diagram or description of inline adapters and patch panels.
- Installation duty: fixed, mobile, repeated flexing, temperature, abrasion, or other environmental exposure.
- Required test methods, acceptance limits, reports, labeling, and packaging.
- Prototype quantity, production volume, target schedule, and any approved alternatives or change-control rules.
If the exact cable is not yet selected, provide the required rate, maximum length, available routing space, bending constraints, and receiver details. A supplier can then review candidate constructions, but final suitability should be approved against the project’s equipment and acceptance plan.
For OEM projects that need a defined cable-and-connector configuration, see OUKETECH’s custom RF and coaxial cable assembly manufacturing page. For broader background on impedance, shielding, and coaxial constructions, use the OUKETECH coaxial cable types and selection guide. If connector selection is the open issue, the coaxial connector types and selection guide provides a related starting point; verify the final part against the equipment and component manufacturer documentation.
Frequently asked questions
Is every 75-ohm coax cable suitable for 12G-SDI?
No. Impedance is necessary, but it does not establish the cable’s attenuation, return loss, connector compatibility, or usable length at the intended data rate. Check the exact manufacturer model and validate the complete path against the equipment requirements.
Can I use a 3G-SDI cable for a 12G-SDI signal?
Only if the exact cable assembly and complete link meet the 12G-SDI requirements at the installed length. A label or prior use at 3G does not confirm adequate 12G margin. Review current cable and connector data and test the actual system where required.
Is 12G-SDI always the best choice for 4K?
Not necessarily. The equipment may support another interface architecture, such as multiple lower-rate links or a different transport. Select the connection method from the system design, cable route, connector density, and required format—not from resolution by itself.
Does continuity testing prove an SDI cable works at 12G?
No. Continuity checks conductor connections and can identify opens or shorts. They do not measure high-frequency loss, impedance behavior, or the receiver margin of the installed path. Specify additional cable or system-level tests when the application requires them.
Can I set one maximum length for all 12G-SDI cables?
No universal length applies to all constructions and systems. Maximum distance varies with cable attenuation, connector transitions, transmitter and receiver performance, and project margin. Use the exact manufacturer distance guidance and confirm the complete path.
Conclusion
Choosing an SDI cable means matching the 75-ohm cable and connector path to the signal rate, installed length, equipment, and handling conditions. Compare exact cable data, count every transition, and treat manufacturer distance figures as product-specific guidance. A well-defined RFQ gives the supplier enough information to quote a buildable assembly and lets the project team verify the actual link before installation.