I am also curious about the cable. At the start of the video, its upper end is clamped on to a part of the antenna. The guy appears to be about take the lower end off what I am guessing is a grounded part, then he decides to give the demonstration. So, in the beginning, is this a live antenna that was shorted to ground while still being powered? (perhaps because it was being worked on?) If so, it seems a rough way to handle the transmitter, though I suppose it must be robust enough to handle lightning strikes (you can see two rods with balls on the end that I guess make a spark gap.)
Alternatively, could this be an unpowered antenna that is picking up signal from a nearby powered one?
Alternatively, could this be an unpowered antenna that is picking up signal from a nearby powered one?
I'm pretty sure this is what's happening. From past experience with high voltage arcs (admittedly at 60hz, not ~1 MHz), I don't think we're seeing more than a few hundred watts of power in that arc. Also, if this tower was actually the one transmitting that signal (presumably 50kW is the transmitter power) they'd shut it off or switch to a different antenna for maintenance on this one. If you shorted the output of the transmitter at the point where it's normally driving a resonant load, the best possible case is that it would trigger some kind of automatic shutdown on the final amplifier.
Alternatively, could this be an unpowered antenna that is picking up signal from a nearby powered one?