People keep declaring SDI dead. Meanwhile it's still bolted into the back of basically every camera, monitor, and router on your truck. SDI isn't dead. It's just not the only option anymore, and knowing when to stay on coax versus when to jump to fiber is the difference between a clean build and a frustrating one.
The SDI ladder, quickly
SDI comes in tiers, and each tier roughly doubles the bandwidth: HD-SDI at 1.5G, 3G, 6G, and 12G. The number is the data rate the cable has to carry, and it climbs with resolution and frame rate. A 1080p signal is happy on 3G. True 4K at high frame rates needs 12G to go down a single coax.
That single-cable part is the whole appeal. One BNC, full resolution, no fuss. The catch is that as the data rate goes up, the cable gets a lot less forgiving.
Why 12G punishes you on distance
Higher frequency signals lose energy faster in copper. The technical name for the problem is return loss, but the practical version is simpler: the faster the signal, the shorter the cable can be before it falls apart.
A 3G run will tolerate a long, mediocre cable. A 12G run on that same cable and length might give you sparkles, dropouts, or nothing at all. This is exactly why a cable can pass 3G fine and choke on 12G. It's not haunted. It's physics. Run good 12G-rated coax, keep it as short as the shot allows, and don't reuse a tired cable for your highest-bandwidth path.
When to stop running coax and pull fiber
Fiber doesn't care about distance the way coax does. Light through glass loses almost nothing over the runs that kill 12G copper. So the rule of thumb is about length and bandwidth together.
- Short 12G run, inside a rack or across a stage? Coax is fine and faster to deal with.
- Long 12G run, across a stadium, a building, or a parking lot? Fiber, every time.
- You need to send a lot of signals down one path? Fiber carries far more in a single, thinner, lighter cable.
The tradeoff is handling. Fiber needs converters at each end, it doesn't love being stepped on, and a dirty connector will ruin your day. Coax is rugged and plug-and-go. Pick the pain you'd rather manage for the run in front of you.
And then there's IP
The third option, and the one taking over the high end, is putting your video on a network instead of a dedicated cable at all. That's the SMPTE 2110 world, and it rides the same kind of fiber and switches that move the rest of the building. Most facilities today are hybrid: SDI where SDI makes sense, fiber for the long hauls, an IP core where they need to scale.
You don't have to choose a religion here. You have to choose the right cable for the run.
The cheat sheet
- 1080p and short runs: 3G coax, done.
- 4K, short run: 12G coax, good cable, keep it short.
- 4K, long run or lots of signals: fiber.
- Large facility, scaling up, remote production: that's where IP and 2110 come in.
Buy quality, label your cables, and match the cable to the job. That's the whole trick.
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