Roy Lewallen wrote:
According to the many references I have, the equation you quote is a
simplified equation that's valid for a single wire over a perfect
conducting ground plane, where the height is a very small fraction of a
wavelength (i.e., radiation is negligible).

Even if everything you say is true, it doesn't nullify the concepts of
physics. Even if the Z0 is changing point to point along the length
of the wire, as it surely does for a vertical antenna, the idea that
standing wave antennas don't possess standing waves is ridiculous.

The idea that the net antenna current on a standing wave antenna is
not itself a standing wave is ridiculous. The idea that the net
antenna current on a standing wave is not the result of the superposition
of the forward current and reflected current is ridiculous. The idea
that RF waves can stand still is ridiculous. The idea that current
flows in only one direction in a standing wave antenna is ridiculous.

A Rhombic, for instance, is a traveling wave antenna. Its feedpoint
impedance is equivalent to its characteristic impedance which is
hundreds of ohms. In a standing wave antenna, it is the reflected
wave superposing with the forward wave at the feedpoint that determines
the feedpoint impedance, low for 1/2WL center-fed dipoles and high
for 1WL center-fed dipoles. The feedpoint impedance depends upon
interference between the forward wave and the reflected wave.

All you have proven is that this is a difficult subject to quantitize,
but we already knew that. It is not a difficult subject to conceptualize.

So, Roy, please answer the following true/false questions.

Standing wave antennas actually exhibit standing waves as described
by Kraus, Balanis, and others. ______

Standing waves are created by the superposition of forward waves
and reflected waves. ________

RF waves cannot stand still. _______ If true, it follows that
"standing" waves are an artifact of superposition and cannot
exist without the two underlying component waves.

What is moving at the speed of light is the forward wave and the
reflected wave. ________ Hint: RF waves must move at the speed
of light. Therefore, RF standing waves have two components, each
moving at the speed of light in opposite directions.

For what it's worth, here's a quote from The ARRL Antenna Book, 15th
edition, page 24-22 under "Single Wire Line": "The characteristic
impedance of the single wire line depends on the conductor size and
the height of the wire above ground, ranging from 500 to 600 ohms
for #12 or #14 conductors at heights of 10 to 30 ft." Nothing said
about "perfect ground" or "small fractions of wavelength".

Again, the concepts that I discuss fall out perfectly from the laws
of physics. That they are difficult to quantify is not a good
reason to adopt a closed mind. (This reminds me of my Southern Baptist
upbringing where some subjects were forbidden).
--
73, Cecil http://www.qsl.net/w5dxp


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