"Richard Harrison" wrote
Nearly every medium wave broadcast station uses a
Faraday screen at every tower between the primary and
secondary of an air-core coupling transformer... Because,
without the screen, capacitive coupling to the tower would
favor harmonics of the broadcast frequency over its
fundamental frequency and make compliance with
FCC rules difficult.
____________

Must politely disagree with that last part -- and probably the first part as
well, at least for modern ACU (Antenna Coupling Unit) designs used in MW
broadcasting.

As a condition of the FCC or other qualification needed legally to offer the
tx for sale, MW broadcast transmitters must meet their harmonic suppression
specs by themselves. They are not permitted to use ACU Faraday screens or
other external means in doing so.

A MW ACU is optimised for maximum power transfer between the transmission
line and the tower for the carrier and its sidebands, however it almost
never uses coupled coils to do that. It uses T, L or Pi networks.

But with or without a Faraday screen, an ACU can couple no more harmonic
energy to the radiator than exists, with respect to the carrier, at the
input of the ACU -- which already meets harmonic suppression specs.

RF