In article ,
Cecil Moore wrote:

Why reflections from the feedpoint if the antenna matches the feedline?

If the antenna is fed with 50 ohm coax, the antenna
does not match the feedline. The Z0 of a #14 wire
30 feet in the air is ~600 ohms. It takes a half-cycle
of sinusoidal RF for the feedpoint impedance to begin
to match the coax Z0, i.e. the feedpoint impedance of
a standing wave dipole is a virtual impedance that
doesn't exist until the first reflections arrive from
the ends of the antenna.

Before Reg died, he had something to say about that.

In the back of "TV and Other Receiving Antennas" by Arnold Bailey is
an interesting section which describes a large number of commonly-used
TV antenna configurations - dipoles made of wire and rod, folded
dipoles with various wire diameters and spacings, bot-tie, simple
Yagi, and so forth.

For each such, Bailey gives two impedance figures - the "surge"
impedance and the feedpoint impedance - which I believe correspond to
the two impedances Cecil is referring to (i.e. before, and after the
standing wave is established).

It's an interesting book... out of print for years, and not (as far as
I know) available electronically.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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