"Ed Price" wrote in message
news
xtNb.5617$A74.242@fed1read02...
...Could you be confusing "omnidirectional" with "omniazimuth"?
... radiation to all points on the horizon, all the way around the
compass.
But that pattern isn't omnidirectional. For instance, what about straight
overhead? Is the field as strong there as at the horizon?
______________
The convention in FM/TV broadcasting is to consider only the radiation
directed toward, and for a few degrees below the horizontal plane when
characterising the shape of a radiation pattern as directional or not. This
is the radiation sector that best serves the purposes of the broadcast
station: to provide the strongest signal to the most receivers. Radiation
toward other elevation angles is largely wasted.
Broadcasters use arrays of antenna elements aligned on a vertical axis to
produce maximum gain in, and near the horizontal plane. Typically each of
these elements is omnidirectional in the azimuth plane, arrayed at about 1
lambda vertical intervals, and driven with equal power and phase.
A slide show and tech papers on these topics are available following the
"Papers" button at
http://rfry.org.
R. Fry