On May 26, 6:59*am, Cecil Moore wrote:
That knowledge can be obtained
from any good optics reference book including "Optics", by Hecht and
"Principles of Optics", by Brown and Wolf.
Continuing after taking my wife to work:
The reason that optical physicists know so much more about energy
transfer than RF gurus is that the optical physicists do not have the
luxury of measuring the voltage and current associated with an EM wave
at light frequencies. They have historically been forced to deal with
irradiance, i.e. power density, at every step of their analysis since
that is the only thing they could easily quantize through
measurements. As a result, they know everything one needs to know
about where the energy goes during reflection and wave cancellation.
If one wants to catch up on such as it applies to all EM waves,
including RF waves, please obtain a copy of "Optics", by Hecht and
read the chapters on superposition and interference. It was an eye
opener for me and resulted in my WorldRadio energy analysis article.
http://www.w5dxp.com/energy.htm
Optical physicists usually make power density (irradiance)
measurements and then calculate the electric and magnetic fields of
the EM wave. RF gurus make voltage and current measurements and ignore
energy/power except for net power in and net power out thus losing
important details in the process. When they don't understand energy
transfer, they dismiss it as unimportant or worse yet, assume that
their ignorance somehow proves something as W7EL has done in his "food
for thought" article on forward and reflected power. All that he has
succeeded in proving is his ignorance of partial or total wave
cancellation involving two superposed component waves which can
reverse the flow of energy in a transmission line just as easily as
can an actual reflection. Here is a diagram of the energy flow at a 50-
ohm Z0-match as is common in ham installations.
http://www.w5dxp.com/enfig3.gif
Pref1 = Zero = P3 + P4 - 2*SQRT(P3*P4)
where P3=P4 and the two electric fields are 180 degrees out of phase.
This is total destructive interference due to wave cancellation, i.e.
out-of-phase superposition.
Pfor2 = P1 + P2 + 2*SQRT(P1*P2)
This total constructive interference due to in-phase superposition.
If W7EL would use the general power density equation on his "food-for-
thought" examples
Ptot = P1 + P2 + 2*SQRT(P1*P2)cos(theta)
he would obtain all the correct answers as to where the reflected
energy goes, i.e. the energy analysis would agree exactly with his
voltage analysis. That energy analysis would tell us exactly how much
reflected power is absorbed in the source resistor and exactly how
much is redistributed back toward the load as part of the forward
wave. But when W7EL heard these facts of physics from the field of EM
wave optics many years ago, he said "Gobbleygook".
--
73, Cecil, w5dxp.com