The Natural Philosopher wrote:
However what is under discussion is nothing more or less than a length
of 75ohm coax, which it is claimed 'will pick up signals in the sheath'

Not "in" - ON the outer surface of the sheath. Completely different
signals can flow on the inside and outside of a coaxial cable. The balun
is to stop interference entering the coax at the open end where it
connects to the aerial.



--
Ian White