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## Re: Topband: GAP Vertical Question

 To: Re: Topband: GAP Vertical Question "Tom W8JI" Tom W8JI Mon, 17 Dec 2012 10:14:31 -0500 mailto:topband@contesting.com>
 Just to be clear, since the discussion drifted to half-wave radiators, my comment above was specific to the modeling of thick v. thin half-wave radiators, including the 180-195 degree radiators of some well-known 50KW AM stations. The results when modeling the base Z of approx. 1/4-wave radiators is less affected by thickness, probably due to a lower base Z to start with. ``` The theory (or cause) behind this is twofold: ```1.) A thicker radiator at an end has a larger area for the electric field. This results in a less concentrated e-field discontinuity or boundary at the open end of the element. In other words the electric field is not as intense, and that means voltage is less. ``` ```2.) Any antenna is also a transmission line. The surge impedance of that transmission line is lower with a larger effective diameter conductor. The mismatch of the open circuit at the far end is transformed through that transmission line, by the standing wave in the antenna, to a new lower impedance at the center, just as the center can be transformed back up to an open end. ``` ```This means a thicker antenna element doesn't have the low and high impedance extremes at the open end or along the antenna that a thinner antenna has. The standing waves are muted. ``` ```If the antenna had no radiation or loss, it would have no end current. It would have infinite impedance. ``` This applies to counterpoises also. ```We can see how difficult it is to have useful things in antennas (antennae are found on insects, and can have zero current) that have no radiation and no loss. :-) ``` ```73 Tom ```_______________________________________________ Topband reflector - topband@contesting.com ```
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