______________________________ Reply Separator
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Subject: Re: [TowerTalk] Steve's antenna study
Author: "Jim Reid" <jreid@aloha.net> at InterNet
To: <towertalk@contesting.com>
Date: 7/21/98 8:28 PM
"That pattern is completely independent from the impedance of the transmission
system and the resulting vswr seen in the transmission line. One is an apple,
the other is an orange. To say the antenna's gain depends upon the efficiency of
the total system is an error. The antenna will produce the azimuth pattern
regardless of the efficiency of conversion of what comes out of the
transmitter down in the shack, and what is left by the time the energy
(power) at last is able to accelerate electrons within the antenna
structure."
Jim:
The above statement is true with following comments.
Once the geometry of the antenna is defined, the antenna pattern will
be the same regardless of impedance, VSWR, etc. In this instance,
antenna gain is not the correct characteristic to discuss but rather,
antenna directivity. Antenna directivity is simply the relative dB
level of radiation intensity at the antenna pattern peak relative to
that of the isotropic antenna. The gain of an antenna would be equal
to its directivity if the antenna were 100% efficient. The gain of an
antenna is therefore equal to the directivity less any losses in the
antenna. These losses include losses in the antenna structure,
matching network and VSWR.
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