W5DXP wrote:

Roy Lewallen wrote:
Magid has the most rigorous derivation of power and energy flow on
transmission lines I've seen, as well as other extensive transmission
line information. One conclusion that pricked my ears was that on a
line with a pure standing wave (e.g., a lossless line terminated with
an open or short circuit), ". . . power (and therefore, energy) is
completely trapped within each [lambda]/4 section of this lossless
line, never able to cross the zero-power points and thus constrained
forever to rattle to and fro within each quarter-wave section of this
line."

He's obviously talking about net energy. There is no impedance
discontinuity
in a continuous piece of transmission line so there is nothing to cause
reflections at the zero-power points. Net energy doesn't cross the zero-
power points but equal forward energy and reflected energy must cross the
zero-power points. That is easy to prove by observing ghosting on a TV set
being fed by 1000 feet of ladder-line. If energy is completely trapped
within each 1/4WL section, ghosting would be impossible.

I forgot to add. At the "zero-power points", either voltage or current is
zero. All that means is that all the energy is contained in the opposite
field. If the voltage is zero, the H-field is at a maximum. If the current
is zero, the E-field is at a maximum. The energy still exists, just in one
field or the other. V*I*cos(theta) is NET energy. The power in the forward
wave is Vfwd*Ifwd and the power in the reflected wave is Vref*Iref. Those
values are constant all up and down the line for a lossless feedline.
--
73, Cecil http://www.qsl.net/w5dxp



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