*The idea that coverage is maximum for the 5/8th wave
radiator is common but in practice, (maybe we are saying the
same thing) a straight 1/2 wave may have a smaller fading
ring because it does not have the high-angle lobe wich
appears on the 5/8th wave pattern.

My comments also were addressing the belief of the OP that the peak
gain of a 5/8-wave vertical was very little different than for a 1/4-
wave, because of a high-angle lobe developed by a 5/8-wave.

It is true that such a high-angle lobe develops to some extent for all
vertical monopoles between 1/2-wave and 5/8-wave in electrical
height. This can be seen in the plots linked below (FCC method).

http://i62.photobucket.com/albums/h8...Comparison.jpg

But regardless, the 5/8-wave has the greatest peak gain of the five
monopoles shown.

In situations where the combination of frequency, earth conductivity
etc (my 6 points above) limits the useful groundwave coverage radius
closer to the transmitter site than is served by the high-angle lobe
from a 5/8-wave radiator, then the 5/8-wave would produce the greatest
fade-free groundwave coverage area day and night (other things equal).

However this isn't the case for most "Class A" (50 kW, non-directional
day/night) AM stations. The most common radiator height used by them
is about 195 degrees, which provides a little more groundwave range
than a 1/2-wave, and about the greatest distance/smallest width for
the fade zone. WJR, in fact, uses a 195 degree vertical.

I certainly agree that patterns calculated for "ideal" ground
are not matched by practical ground systems except, perhaps,
sea-water grounds.

The FCC approach for AM broadcast stations is to use the pattern/gain
of the radiator over a perfect ground as a basis for the groundwave
field intensity at a given distance over real ground, as determined by
the FCC's MW propagation curves -- which curves are based on real-
world, measured performance.

With the advent of NEC and NEC-2, some have been misled by the
elevation pattern shown for a vertical radiator at an infinite
distance over real ground as being that of the radiation launched by
that vertical radiator. But it is not, it is only the amount of that
original radiation that survives at an infinite distance, for those
ground conditions (and for flat earth, at that).

This has led to the concept of a "take-off angle" from a ground-
mounted vertical where peak radiation occurs, and that little to no
radiation occurs from the monopole in and near the horizontal plane.
But that isn't the case -- the relative field over real ground at low
elevation angles close to the vertical radiator can be very high, and
will continue onward to produce a long-range skywave. Even radiation
at an elevation angle of one degree will reach the ionosphere, due to
earth curvature.

The theoretical elevation patterns shown in my plots don't exist very
far from the antenna, but they are a closer to reality over real
ground than those shown by NEC and NEC-2 for an infinite distance over
the same ground, and assumed also to exist close to the radiator.

The results obtained using NEC-4 to calculate the groundwave field
intensity within the useful daytime coverage areas of AM broadcast
stations give much better correlation to the measured fields, and to
the methodology of using the theoretical pattern with the FCC's MW
propagation curves.

RF