Just a quick report on a failure mode for LF TX antennas.

Last Fall my original TX loop made up of approximately 500 feet of RG-11 coax suspended from trees went open circuit (both center conductor and shield), some time later part of the wire actually came down. I had thought that abrasion from contact with the trees had eventually worn through it.

What I found was a little more interesting. Looking at the downed end, it appeared that the insulation had melted for a considerable distance and there were burn marks further up the cable. My hypothesis is that the outer insulation was abraded away and the coax shield came into contact with the tree limb causing the burning/melting. 

Will try to get some pictures this weekend and put them up on my website.

Long term if one wants to operate at the kW level either better insulation or a better way of supporting the antenna than trees would be required!