On Sun, 27 Mar 2005 10:01:23 -0500, Tom Rauch wrote:
>but for longer feedlines 75 is a good option.
Yes. I'm still a fan of 75 ohm cable for dipoles that are relatively
high (as a fraction of a wavelength) and otherwise in the clear, and
50 ohm cable for those that are relatively low. The reason -- if you
study models in the various texts (ON4UN, and others) for the
impedance of dipoles, they tend to vary around 50 ohms +/- 33% for
low dipoles, and around 70 ohms +/- 33% for higher ones. In other
words, the presence of ground affects the feedpoint impedance, but
tends to approach 70 ohms as the antenna gets further from ground.
Jim Brown K9YC
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