"Dave Platt"
... On the other hand, given the comments by Cebik and others
about the somewhat illusory nature of the gain advantage
of a 5/8-wave, I may just stick with J-poles and quarterwave
ground planes.
_______________

Just to note that for AM broadcast verticals, the FCC requires a certain
antenna "efficiency" for various classes of stations, in terms of the
minimum ground wave field strength produced per kilowatt of input power to
the radiator.

The FCC field strength minimum cannot be met by "Class A" stations
(basically the 50kW-ers) using a 1/4-wave vertical radiator. At least a
1/2-wave radiator is needed in most cases.

The most common radiator height for Class A non-directional AM broadcast
stations operating at 50kW day and night is 195°. A radiator height of 225°
(5/8 wave) maximizes ground wave field strength at a given power, but also
produces a high-angle lobe that can interfere with the ground wave during
night-time operation -- so rarely is used by AM broadcast stations. The
ground wave field strength difference between 195° and 225° radiators is
fairly small.

RF
Former staff engineer, WJR Detroit -- (Class A, 760kHz)