[TowerTalk] dipole in space question

[Jim Brown]

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