I have just finished a SD multi-cam live show and low and behold one of the camera BNC feeds into the vision mixer has horizontal lines through the video signal. I have come across this before when running BNC video cable next to a powered cable, it is creating 'noise' in the video signal (slight fuzziness and moving horizontal lines). Now the BNC cable we have been provided is around 200 feet, we have tested this at full length outside with no powered cables near by, and no noise occurred and the picture was a clear as day, which rules out any need for a DV signal repeater. My question is, would high quality 'Sheilded' BNC cable be better running near powered cables from the audio & lighting guys? as sometimes there is limited space for live shoots, and what with health an safety measures, there is no other option but to run next to their cables. Is shielded cable going to work? Can it shield from powered cable to give me a noise free picture? Have you come across this before? Any advice would be appreciated greatly.
IME, a video isolation transformer would be much more likely to reduce or eliminate that kind of noise. (Unless you are using low-quality coaxial cable without 100% shield coverage.) I always keep a couple of video iso transformers in the kit just for this kind of problem.
This is probably not caused by induction from nearby AC cables, but is just common 'ground loop', or AC hum. Anytime there is a difference in potential on the ground side of equipment chassis, this can happen. It is very common on large remotes, and not confined to video. A hi-pass 'hum-bucker' type filter, or iso transformer often eliminates the hum.
Other things you can do is power everything from the same circuit, or sometimes you can use (in the USA) those 3 prong ground adapters (we call them 'ground lifts') on the offending gear to keep stray AC from coming up the ground.