Roy Lewallen wrote:
Here's an interesting quote from _Transmission Lines, Antennas, and Wave
Guides_, by King, Mimno, and Wing: *It
is fundamentally incorrect to treat a center-driven antenna as though it
were the bent-open ends of a two-wire line.*

Funny, I thought Maxwell's equations worked for either case. Did you also
know that *It is fundamentally incorrect to treat a wolf like a dog.*

If you slowly increase the spacing and angle between the two conductors
of a transmission line, at exactly what spacing and angle does it magically
cease being a transmission line and become an antenna requiring a completely
different treatment? Please be specific as to the exact spacing and angle at
which it becomes "fundamentally incorrect" to treat the configuration as a
transmission line. Incidentally, I don't usually use circuit theory for
transmission lines.

Your current distribution curve displayed by EZNEC for a 1/2WL dipole
looks exactly like Fig 1, page 2-2, ARRL Antenna Book, 15th edition. I thought
you or Walt probably wrote that section. If you had displayed both the current
and the voltage distribution in EZNEC, what would it look like for a 1/2WL dipole?

We can easily measure the impedance at any point along a 1/2WL section of
transmission line with reflections or the feedpoint impedance at any point
along a 1/2WL dipole. As you know, those impedances are the ratio of net
voltage to net current. At the impedance minimum on a transmission line,
the voltage is minimum and the current is maximum. Same for a feedpoint
impedance minimum on an antenna. At the impedance maximum on a transmission
line, the voltage is maximum and the current is minimum. Same for a feedpoint
impedance maximum on an antenna. We can deduce the ratio of the voltage to
the current from the feedpoint impedance - or is that one of the rules of
physics that a transmission line obeys but an antenna disobeys?
--
73, Cecil http://www.qsl.net/w5dxp



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