[TowerTalk] resonance/swr/impedance plots

[Bill Coleman]

On 11/29/00 21:09, Guy Olinger, K2AV at k2av@contesting.com wrote:

>You will hear people talk like that and everyone knows that they mean to
>tune the antenna's feedpoint impedance for purposes of matching a
>feedline. Some people will say self-resonant to underscore that they
>really mean resonance, not tuneability.

But if you look at the matching network and antenna as the antenna 
SYSTEM, isn't it the same thing? 

>It doesn't matter whether a lumped constant is at the feedpoint or up
>the whip, a 10 foot whip is not [self-]resonant on 75 meters. You CAN
>use various tuning devices to force power into it at the ridiculously
>high current levels involved. A sixty-something foot long whip is
>[self-]resonant. A tuned up 10 foot whip on 75 has the APPEARANCE of
>resonance. But it has FEW of the ADVANTAGES of resonance, like
>efficiency and bandwidth.

This debate has raged on before. The issue isn't resonance at all, but 
loss. If a 10 foot whip is matched on 75m, the antenna system is 
resonant. However, it is likely to have lots of losses that a sixty-some 
foot whip doesn't. If one could design a lossless matching network, the 
efficiency of the 10 foot whip would approach that of a sixty-some foot 
whip. If the whips were lossless, then the antennas would act the same. 
(Conservation of energy -- if there are no losses, then all of the RF 
energy entering the antenna system must radiate)

There's nothing magic about resonance in the antenna element. The key 
issue is loss. Eliminate the losses, and it works the same, resonant or 
not. 





Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901


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