Re[2]: [TowerTalk] Steve's antenna study

[sbest@cushcraft.com]

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     Subject: Re: [TowerTalk] Steve's antenna study
     Author:  "Jim Reid" <jreid@aloha.net> at InterNet
     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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