Low voltage, too much jitter, old BNC connectors, worn out cable, or, most likely, a combination thereof.. The great news is that, with a <$200 analyzer device you can visualize and isolate the problem, whereas in the past it would have cost over $8,000. You need a device to see the EYE pattern of the SDI signal. Try this device: Lumantek ez-SHV+. There's one on eBay right now for $165. The solution to your actual problem is probably cut the Medusa cable in half, and put new connectors on all ends. That's what, 12 connectors? Solvable problem for a little bit of cash. The connectors are probably about $3 a piece, and you'll need, I guess, 12 of them. Plus, a cable stripper and crimper. You're into $300-ish. Or, around $500 if you also go for the analysis tool. Best of luck!