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Old November 4th 03, 09:43 PM
Roy Lewallen
 
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I'm not sure why anyone would think that you can treat an antenna, or a
loading coil of significant length, as a lumped element and expect to
get anything resembling accurate results. Who in the world is proposing
such a thing? Or is this something to be attributed to the "old wives"
and "gurus", so we can then show how much smarter we are by pointing out
how stupid it is?

Gee whiz, golly, yes, representing an antenna as a two terminal black
box with zero size presents a problem. And no, you can't put a box
around anything having any length and expect the current in to equal the
current out. And why should this be surprising to anyone?

Yes, a solenoid produces a local (near) field in the direction of its
axis. The far field that remains depends on the size and aspect ratio of
the solenoid. Hence, we have solenoidal antennas that radiate primarily
axially and those which radiate primarily radially. It's not clear to me
how this bears on the topic.

Jim Kelley wrote:

Jim Kelley wrote:

What if you draw a two terminal black box around the middle few feet of
a 1/4 wave vertical? What makes the sum of the currents at both ends
become equal to zero?



Sorry to be obtuse, Roy. The point is only that antenna circuits
obviously present a problem to the assumption that such two terminal
black boxes will necessarily have equal currents at both terminals.

A solenoid should produce a field in the direction of its axis, should
it not?

73, Jim AC6XG


 
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