RadioBanter - View Single Post

May 13th 06, 03:26 PM posted to rec.radio.amateur.antenna

wrote:
There's a good fight brewing in QEX magazine land. Eric, K8LV, wrote a
pretty good article on directional wattmeters. But he spent a lot of
space asserting that the notion of forward and reflected power in a
transmission line is merely for intuitive convenience, isn't real, and
should be abandoned in favor of unidirectional power flow and lumped
analysis at a single point.

K8LV is like the person who is satisfied with the Sun God riding
his chariot across the sky every day as a model of reality. He seems
to believe in a Standing Wave God who wills standing waves into
existence without the necessity for a forward traveling wave and
a rearward traveling wave to exist. It reminds me of what Einstein
said about models of reality needing to be simple, but not too simple.

Over the years, I have challenged anyone on this newsgroup to create
a standing wave in a single source system without having the existence
of a forward wave and a reflected wave. Nobody has furnished any proof
that standing waves are possible in a single source system without the
existence of forward and reflected waves.

Reflected energy is readily apparent using a time domain reflectometer.
Reflected power is easily detected and dissipated using a signal
generator with a circulator and load. A bit of modulation proves that
the reflected wave has made a round trip to the mismatched load and
back to the circulator load.

With the following example, I have shown that, during steady-state,
there are 300 joules of energy in the transmission line that have
not yet reached the load.

100W---one second long 50 ohm lossless feedline---291.5 ohms
Pfor=200W-- --Pref=100W

There are no impedance discontinuities between the source and the
load and EM energy travels at the speed of light. The 300 joules
cannot exist anywhere except in the forward and reflected waves.
Without the existence of forward and reflected waves, there is
nothing to support standing waves. That the energy moving in each
direction is difficult to separate is no reason to assert that it
doesn't exist. According to the IEEE definition of power, the
*potential* for doing work is power. The 300 joules stored in the
above transmission line have the potential for doing work after
the source is powered down. That the work actually performed is
not useful work is irrelevant.

Anyone who doubts the existence of reflected energy should do a
second by second analysis of the above example starting at power
up. The technical facts become undeniable after a few seconds.

Whoo Hoo. The letters will be fun. Especially if Eric attempts to
extend his assertion to a case not-as-special, such as not-steady-state
or a point in 3D space.

Too bad it wasn't here. Bet we'd get a couple dozen posts before the
weekend's out. Anyone want to take Eric's side?

K8LV even contradicts himself in his own article. He says the Z0 of
the line "literally forces all power flow to occur in 50-ohm waves
on the line". In the above example, those 300 joules per second are
necessarily flowing in the one second long line since they cannot
stand still. Where are they if, as K8LV asserts, the Z0 of the line
is forcing a V/I ratio of 50 ohms? They can exist in only one place,
in the 200W forward wave and 100W reflected wave each of which forces
a V/I ratio of 50 ohms, just as K8LV asserts.

Exactly the same thing happens when standing EM waves of light are
formed in free space. Let's see K8LV explain that one without the
existence of forward traveling light waves and rearward traveling
light waves. How do these quotes agree with standing waves of light?

"... the forward and reverse waves do not exist separately ..."

I think I can hear a multitude of physicists laughing at the assertion
that standing waves of light do not require the separate existence of
forward and reverse waves. QEX was interested in publishing an article
of mine with light wave examples until they realized the implications
of those technical facts.

This is just one more example of the dumbing down of amateur radio
accompanying the dumbing down of the US educational system in
general. Unfortunately, it seems to be a trend that cannot be
reversed because it is the biased view being pushed by the ARRL
and its supporters.
--
73, Cecil http://www.qsl.net/w5dxp