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Old 03-20-2016, 06:45 PM   #19
NN5I
Carl, nn5i
 
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Join Date: Sep 2011
Location: Tallahassee, FL
Posts: 1,441
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Quote:
Originally Posted by N3LYT View Post
I guess the bottom line with a vehicle is ground loss not ground plane.
That's one of the two important bottom lines. The other, of course, is the effect on radiation pattern.

My old friend Whit Griffith, N5SU (SK), whose career for decades was designing and building large HF station transmitters and antennas (Voice of America, Radio Free Europe, etc.) knew more about antenna efficiency and antenna patterns (not to mention HF amplifier design) than I know about everything I know about. He once ran an experiment with a large (large!) HF vertical. He calculated the radiation resistance, then measured the input impedance with one radial, two radials, etc., up to (if I remember) a hundred or so radials. This enabled him to calculate the efficiency of the whole antenna system at each step. Whit presented the results at the Dallas Amateur Radio Club in 1982 or so. He found that anything more than 25 or so radials yielded only a little improvement, but fewer than 10 or so caused the station, to a considerable extent, to cook worms instead of radiating a signal.

As Whit explained for those of us whose expertise didn't match his, the purpose of the radials (or other ground conductors) can be looked at as shielding the soil from your signal so the signal won't be absorbed in the soil and your transmitter's power be wasted cooking worms.
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