On Sun, 6 Jul 2008 20:28:49 -0700, Alfred Lorona wrote:
>One way to eliminate it is to use a quarter wavelength long feedline with a
>good earth ground at the station end. The impedance at the ground end is
>ideally 0 ohms and the far end of the feedline shield looks like, ideally,
>an open circuit. The Rf current does not flow into an infinate impedance of
>millions of ohms! Worse case scenario is a feedline one half wavelength
>long. The impedance of the shield to the Rf at the dipole center is now zero
>ohms. The RF will love that!
>It is extremely difficult to avoid a common mode current unless the antenna
>is perfectly symmetrical in every respect to it's surroundings; situation
>hardly every achieved in a practical installation.
Al,
You're right on target about antennas being unbalanced by their surroundings,
but you're in the dark ages with respect to solutions to this problem. See
http://audiosystemsgroup.com/RFI-Ham.pdf and
http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf
The chokes described in my "cookbook" will virtually kill common mode current.
And these are multi-band solutions! You do NOT need to go to the trouble of a
resonant line.
73,
Jim Brown K9YC
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