Brenda Ann Dyer wrote:
There are ways of broadbanding an AM tower. One way is to add longwire
antennas in parallel to the main tower, stood off by a couple feet or so. I
helped install such a system in Portland, Oregon a few years ago.

True, though in most cases I would think the narrowband problem is in
the matching network, (especially at highly-directional stations) not
the individual tower(s).
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com