On Thu, 12 Jun 2008 08:59:20 -0700, Al Williams wrote:
>Yes the current is strongest at the center, but why?
>From a current/voltage point of view, an antenna can be thought of
as a transmission line of that length. Current and voltage along a
line varies as a standing wave and repeat in half-wavelengths. Since
the END of the antenna is an open circuit, the current MUST be zero
at the end, and the voltage is a maximum. A mathematician would call
this a "boundary condition" for the equations he would write.
1/4 wavelength from the end the CURRENT reaches its maximum and the
VOLTAGE drops to its minimum. The dipole is resonant at the
frequency where it's a quarter-wave length to each end (or an odd
number of quarter wavelengths to each end) because this makes the
standing wave patterns "nice" -- that is, they reinforce each other.
It's like a resonant circuit, where energy is traded back and forth
between the L and the C when XL = XC.
73,
Jim Brown K9YC
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