Effective radiated power is a widely misunderstood concept.
Effective radiated power is the term that describes station
output, including the transmitter, antenna and everything in
between, when considering transmitter power and system gains and
losses. (E9H04) The effective radiated power, or ERP, is always
given with respect to a certain direction. Let’s think about
this for a second. If your transmitter has an output of 100 W,
the maximum power that the antenna can radiate is also 100 W.
Transmitting antennas are, after all, passive devices. You can’t
get more power out of them that you put into them. In reality,
the total power output will be even less than 100 W because you
will have losses in the feedline. An antenna can, however,
concentrate the power in a certain direction. The power being
radiated in that direction will be more than the power radiated
in that direction by a reference antenna, usually a dipole or an
isotropic antenna, which is an antenna that radiates equally in
all directions. When a