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Old March 25th 09, 12:45 PM posted to rec.radio.amateur.antenna
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Default colinear representation in NEC

Jim Kelley wrote:
The only current flowing on an antenna is the current traveling from one
end to the other.


Since standing waves cannot exist without the underlying
component traveling waves, to avoid conceptual blunders,
one needs to deal directly with the component traveling
waves. Your statement is based on a purely mathematical
shortcut which exists only in the human brain, not in
reality, and obscures the actual speed-of-light physics
necessary for an EM wave to even exist.

The current can be artificially parsed the way you
are doing it but that parsing leads to the very
misconception under which you are laboring. The same
thing happened with w8ji's and w7el's "measurements"
involving delays through loading coils. The actual
component physics, as explained in any reasonably
technical antenna book is:

Total current = forward current + reflected current

Itot = Ifor + Iref (phasor addition)

Reference: "Antenna Theory", Balanis, 2nd edition

Balanis, page 488:
"The sinusoidal current distribution of long open-ended
linear antennas is a standing wave constructed by two
waves of equal amplitude and 180 degrees phase difference
at the open end traveling in opposite directions along
its length. ... The current and voltage distributions
on open-ended wire antennas are similar to the standing
wave patterns on open-ended transmission lines."

Balanis, page 489:
"Standing wave antennas, such as the dipole, can be
analyzed as traveling wave antennas with waves
propagating in opposite direstions (forward and
backwards) and and represented by traveling wave
currents, If and Ib in Figure 10.1a."

In a standing wave antenna, e.g. a 1/2WL dipole, there
exists a forward wave that gives up about 10% of its
energy content to radiation. The remaining 90% of the
wave encounters the open end of the antenna and is
reflected. So, just as in the case of an open-circuit
stub, we have a forward current component flowing in
one direction and a reflected current component flowing
in the other direction. Many of the mistakes and mis-
conceptions about antennas are based on your false
assertion above.

I have the ARRL Antenna Book.


:-) The ARRL Antenna Book doesn't even have "traveling
wave antennas" in its index. It does state: "Unterminated
long-wire antennas are often referred to as 'standing
wave antennas'". Please reference a reasonably technical
antenna book like "Antennas", by Kraus. "A sinusoidal
current distribution (on a standing wave antenna) may be
regarded as the standing wave produced by two uniform
(unattenuated) traveling waves of equal amplitude moving
in opposite directions along the antenna."

I wonder if anyone is buying it?


It doesn't matter if anyone is buying it. What matters
is technical validity. Your first statement above is
technical invalid. Given the free space description of
standing waves of light given by Hecht in "Optics", your
assertion above would lead one to believe that the photons
comprising the standing wave of light must be at rest even
though that's an impossibility (except in the human mind).

Here's what a couple of references say about standing waves.
"Electrical Communication", by Albert:

"Such a plot of voltage is usually referred to as a
*voltage standing wave* or as a *stationary wave*.
Neither of these terms is particularly descriptive
of the phenomenon. A plot of effective values of
voltage, appearing as in Fig. 6(e), *is not a wave*
in the usual sense. However, the term "standing wave"
is in widespread use."

"College Physics", by Bueche and Hecht:

"These ... patterns are called *standing waves*, as
compared to the propagating waves considered above.
*They might better not be called waves at all*, since
they do not transport energy and momentum."
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand
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