[BC] High Gain vs Low Gain Antennas

[Richard Fry]

In the "lpfm question" thread I posted:

For all practical purposes a high-gain, omni antenna with beam tilt can
radiate close to the same ERP in the elevation sector serving its useful
coverage area as if a low gain, or even an isotropic radiator was used.
That radiation doesn't go over the heads of the receivers it is intended to
serve, or need to serve them mostly with scatter.

Below to illustrate this is a plot comparing the field intensity from a 
6-bay antenna with no beam tilt or null fill to a 14-bay antenna with 0.6 
degree beam tilt and no null fill.  The same radiation center and same ERP 
was used for each.

Certainly the two antennas provide equal service over the huge percentage of 
the coverage area.

Null fill can be specified for either/both antennas if there is any 
significant population within 5 miles of the transmit site.

The challenge in this is ensuring that antennas actually radiate the az/el 
patterns expected from them.

TV antennas pretty much do that.  Sidemount, non-panel FM antennas, not so 
much.

http://i62.photobucket.com/albums/h85/rfry-100/CoverageComparison.gif

RF