Have you experience running 100w into one of these transformers
yourself? I kinda doubt they would take any watts.

If I understand you correctly you are talking about the little unit
that connects the cable to the old 300ohm input of 1970s type tv.
These units have very small toroids, only maybe a quarter inch in
diameter, that are designed for microvolts of excitation at the bottom
end of TV band - which is somewhere near say 50Mhz. They will not
handle any magnitizing flux and I would bet a watt at 20m would
overheat it.

regards,
Bob
N9NEO