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SDI (Serial Digital Interface) cables carry uncompressed professional video over 75 Ω coaxial runs. Standards have evolved to accommodate higher data rates: original SD-SDI (~270 Mbps for 480i/576i), HD-SDI (1.485 Gbps for 720p/1080i), 3G-SDI (2.97 Gbps for 1080p60), 6G-SDI (6 Gbps for 4K30), and 12G-SDI (12 Gbps for 4K60). In practice, 3G-SDI is used for full HD video, while 12G-SDI (four times the bandwidth) is required for single-cable 4K/60 fps signals. (Even higher formats like 24G-SDI for 8K are emerging, but 12G remains the broadcast workhorse.)
3G-SDI vs 12G-SDI: Performance and Use Cases
When choosing between 3G-SDI vs 12G-SDI, consider resolution and frame rate. A 3G-SDI link (≈approximately 3 Gbps) reliably carries 1080p video (including 1080p60), making it ideal for HD content and most studio applications. By contrast, 12G-SDI (≈approximately 12 Gbps) handles 4K video at 60 fps on a single cable. In practical terms, use 3G-SDI for HD broadcasts, live streams, or event feeds, and upgrade to 12G-SDI for 4K cinema or high-end production. (For ultra-high-bandwidth needs like 8K, multi-link or fiber solutions may be required.)
Key Features: Stability, Shielding, Distance
SDI cables use a solid copper core and layered shielding to protect the signal. The image above illustrates typical SDI coax construction (e.g., RG-6 style): a central conductor, dielectric insulator, and dual shields (foil + braid) that reject interference. This robust design gives SDI its signal stability. Because SDI carries uncompressed digital video, the quality remains pristine over long runs. The 75 Ω BNC connector also secures the cable in place, preventing drops even when the cable is moved.
Compared to HDMI or consumer cables, SDI’s advantages are clear: it can run hundreds of feet with minimal loss, whereas HDMI typically tops out at around 25 meters without repeaters. In a video transmission cable comparison, SDI surpasses HDMI and RCA in terms of distance and reliability. (For example, RG-6 SDI coax can carry full-HD up to ~100–200 m; RG-59 is more lossy and best kept below ~100 m.) If you need still longer runs, active extenders or optical fiber may be required.
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Coaxial Cable Types (RG-59, RG-6, RG-11)
Not all coax is the same. Choose cables rated for SDI’s bandwidth and distance:
- RG-59 (0.64 mm conductor): Thin, single-braided shield. Inexpensive and very flexible, but with higher loss. Suited to analog video and short CCTV runs (<100 m). It can carry HD-SDI, but only over limited distances.
- RG-6 (1.02 mm conductor): Thicker, dual-shielded (foil + braid) coax. Standard for HD/3G-SDI, with lower loss (~2.3 dB/100 ft at 100 MHz). Supports 1080p signals up to ~150–200 m. RG-6 is the go-to for most broadcast installations.
- RG-11 (1.63 mm conductor): Very thick conductor, very low loss. Used for long-distance links (e.g.,>200 m). It can carry 6G/12G-SDI (4K) over ~300 m, but is bulky and stiff to install.
Always match the cable impedance to 75 Ω for SDI; using the wrong type (such as older analog RG-59 CCTV coax) causes reflections and dropouts. For any run approaching the cable’s limit, plan for equalizers or fiber instead.
SDI vs Other Video Cables
In video transmission cable comparisons, SDI stands out as the preferred choice for professional AV applications. SDI (BNC/coax) offers a longer reach and provides locked connections; HDMI (flat jack) is suitable for consumer gear but loses signal beyond ~15 meters. Unlike HDMI, SDI carries only video (audio is sent separately), but this is acceptable in broadcast, where other channels handle audio. RCA and VGA are obsolete for high-res work. Fiber-optic links surpass coaxial cables in distance and bandwidth, but they require converters. For most studios and live events, SDI remains the practical choice.
| Feature | SDI (Coax, BNC) | HDMI (Consumer) | Fiber-Optic |
|---|---|---|---|
| Signal | Digital only, uncompressed video | Digital AV (compressed possible) | Digital video/data |
| Max Distance | ~100–300 m (depending on cable) | ~5–15 m (without boosters) | 500 m+ (with transceivers) |
| Interference | Very low (thick shields, 75 Ω) | Moderate (consumer cable) | None (immune) |
| Typical Use | Broadcast, professional video, CCTV HD-SDI | Home theater, PCs | Ultra-HD links, data centers |
SDI Cable Selection Guide
Choosing the right SDI cable involves matching cable specs to your system’s requirements:
- Format & Bandwidth: Ensure the cable’s rating meets your SDI standard. For example, 3G-SDI cables (rated ~3 Gbps) are suitable for 1080p60, whereas 12G-SDI cabling is required for 4K/60fps content. If you anticipate future upgrades (e.g., moving from HD to 4K), plan cables for the higher data rate.
- Length: Keep HD-SDI (3G) runs under ~150 m on RG-6. For longer distances, use RG-11 or active repeaters. For 12G-SDI (which operates at higher frequencies), shorter runs (≤100–150 m) are safer.
- Shielding & Environment: Use dual-shielded cables (foil + braid) to minimize EMI in studios or outdoors. Plenum-rated or outdoor wires may be required for specific installations.
- Connectors & Impedance: Use 75 Ω BNC connectors top-to-bottom. Mismatched connectors (50 Ω) or damaged BNCs can degrade SDI signals.
- Budget vs Performance: Higher-grade cables (e.g, RG-11) cost more. If distances allow, RG-6 often provides the best cost/performance for HD-SDI. For marginal runs, consider boosters.
Follow these steps in your SDI cable selection guide to choose the ideal cable: match the cable rating to the required data rate, select the appropriate RG type based on the length, ensure proper connectors and shielding, and add amplification if necessary. When in doubt, overspec the cable. Even if 3G-SDI “works” on cheaper coax, using a 6G/12G-rated RG-6 will improve headroom and reliability.
Real-World Use Cases
SDI cabling is everywhere in AV:
- Broadcast TV: For studio cameras and switchers, 3G-SDI (HD) and 12G-SDI (4K) cables carry signals from cameras to mixers. These high-speed links require RG-6 (dual-shield) to avoid any dropouts.
- Live Events: In concerts and sports, long coax runs deliver multi-camera feeds. Here, RG-11 may be used on cable towers for its distance headroom, or fiber-optic “SDI extenders” if runs exceed coax limits.
- Security Systems: Traditional CCTV used analog coax (RG-59), but modern HD surveillance uses HD-SDI over RG-6. In practice, engineers select RG-6 for HD cameras and are careful to maintain 75 Ω throughout.
- Testing & RF: In labs, 50 Ω coax and BNC connectors are used for RF signals (oscilloscopes, etc.), not for SDI. Professional video always utilizes 75 Ω components.
SDI Cable FAQs
A: 3G‑SDI (SMPTE 424M) runs ~3 Gbps for up to 1080p60 HD video, whereas 12G‑SDI (SMPTE 2082) runs ~12 Gbps to carry single‑link 4K at 60 fps. In other words, 12G‑SDI has four times the data throughput of 3G. Use 3G-SDI for HD workflows and 12G-SDI for full 4K/60 performance.
A: Cable length depends on bitrate and cable quality. On good 75 Ω coax, legacy HD-SDI (SMPTE 292M) can reach ~100 m, but 3G-SDI (1080p60) drops to ~50–60 m. Even top-tier cables typically limit 12G-SDI (4K60) to ~40–70 meters. For longer distances, use active repeaters or switch to fiber.
A: RG‑59 is a thin 75 Ω coax (20 AWG) with higher signal loss – fine only for short runs. RG-6 (18 AWG) is thicker with lower attenuation – the standard choice for moderate runs (tens of meters). RG‑11 (14 AWG) is the thickest with the least loss; e.g., Belden 7731A RG‑11 reaches ~120 m at 3G‑SDI. In practice, use RG‑59 for short links, RG‑6 for typical runs, and RG‑11 when you need maximum length.
A: SDI is the professional standard: it uses locking 75 Ω BNC connectors (no HDCP) and can run hundreds of feet (often ~300 ft or ~100 m) without repeaters. HDMI is consumer-oriented, non-locking, typically uses HDCP, and usually maxes out at around 15 m (50 ft) without extenders. In short, SDI’s robust connectors and long reach make it ideal for broadcast/studio use, while HDMI is better suited to brief, consumer setups.
A: Yes. Manufacturers can custom-assemble SDI cables to your needs. You can specify any length and jacket type (plenum, outdoor, armored, color-coded, etc.), as well as the cable medium (coax, triax, or fiber for very long runs). Custom assemblies can include multiple BNC connectors, hybrid cables (e.g., SDI with power), or multi-cable bundles as needed.
A: SDI carries uncompressed digital video, so loss appears as a sudden dropout rather than a fade. High-frequency (12G) signals attenuate more quickly, so long runs require low-loss coax and often employ equalizers. Good shielding (multi-layer foil + braid) is vital for blocking external RF/EMI. In practice, use quad-shielded 75 Ω cable and quality BNC connectors. Every connector and bend adds a bit of loss, so keep runs neat and, if necessary, use repeaters or equalizers before image issues appear.
A: SDI uses 75 Ω BNC connectors, so always match impedance. Do not use a 50 Ω connector on 75 Ω cable – that causes reflections and signal loss. Some professional equipment uses mini versions (HD-BNC or DIN 1.0/2.3), but these are also 75 Ω. In short: ensure every cable, plug, and terminator in an SDI system is 75 Ω to avoid mismatches and signal errors.
Conclusion
Selecting the right SDI cable ensures rock-solid video transmission. Key factors are data rate (3G vs 12G), cable construction, and run length. With proper 75 Ω coax (typically RG-6 or RG-11) and BNC connectors, SDI links can span large venues or broadcast studios with complete signal integrity. In most AV scenarios, SDI outperforms consumer cables in stability and reach.
For projects requiring specialized solutions, Romtronic’s custom SDI cables and consulting services offer a professional option. We can design custom cable assemblies (coax or fiber) tailored to complex requirements. In short, understanding SDI cable types and features, combined with expert vendor support, ensures your video system remains crisp and reliable.
Alex Wang is the Marketing Manager at Romtronic, with a degree in International Business and over seven years of experience in the electronic cable and wire harness industry. He leads marketing efforts across North and South America, combining deep industry knowledge with strong sales experience.
In addition to overseeing global marketing strategy, Alex is also responsible for content development and editorial coordination, ensuring that Romtronic’s messaging remains clear, consistent, and engaging. His strength in market analysis and customer-focused approach helps clients make more informed purchasing and sales decisions.
