On 9/11/2011 3:27 PM, ZR wrote:
> It doesnt matter what the radiator length is, the maximum FEED current is at
> the base if its a base fed antenna.
Not true. The voltage and current distribution of the antenna is
established by what engineers who have studied calculus would call a
boundary condition and those who have not would call common sense --
that is, the current MUST be minimum and the voltage MUST be maximum at
the open end. Further, we know that the current and voltage
distribution of this relatively simple antenna vary from max to min
every quarter wave along the antenna, just as they do along a
transmission line with an open circuit at one end.
Consider a half wave antenna fed at the base (which I've done with a
tapped inductor configured as a step-up auto transformer). The current
is at a minimum at the base and the voltage is at a maximum, making it a
very high impedance feedpoint. Consider an antenna that is electrically
about 3/8 wave -- the current still must be minimum (and the voltage a
maximum) at the open end, and the current maximum is 1/4 wavelength down
from there, 1/8 wave above the feedpoint. Now, the current at the
feedpoint in this case is still significant, but it is quite a bit down
from maximum.
73, Jim Brown K9YC
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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