Reg, G4FGQ wrote:
"What proportions of U.S. broadcasting stations have antennas consisting
of more than two towers?"

I don`t know but from my own experience, the number is large. A new
applicant for a station must show he will not interfere with existing
stations by limiting his radiation in the directions of the existing
stations while providing minimum field intensity, 0.5 to 50 mV,
depending on population, in the new service area. A two-tower array
cannot satisfy some complicated pattern requirements.

Most broadcasters want to provide more than 1 KW radiation in their
areas. Well over one hundred channels in the medium wave broadcast band
in North America allow that. There are well over 1000 regional medium
wave broadcasters in North America. It is difficult to fit a new
broadcaster in when he wants to use real power.

Best regards, Richard Harrison, KB5WZI