Many moons ago I was the dispatcher at Cablevision of Charlotte. Had a complaint regarding ch.2 /6m TVI and when I saw the address I realized it was in the same block as an acquaintance of mine (Ed) who was a big 6m guy. I mentioned it to him and he said he had never heard of any complaints. There was an AC power supply for the system on a pole in front of his house. I asked the tech for the area to take a special look at this and he obliged. Problem found. Normally AC power is inserted on the cable with a device called a 'power inserter'. In other disciplines they use different terms like 'diplexer' for this function but the idea is the same in that there is no RF continuity on the AC port. Someone had used a power passing directional coupler here. You can't tell them apart standing on the ground. The tech spotted that and replaced it with the correct device and that was the end of that.