Richard Harrison wrote:
I have not tried my Bird wattmeter on this. Maybe Cecil has and will say
I am wrong.

No, I agree with your analysis, Richard, as far as it goes
but an expanded look will reveal some interesting facts.

Concerning open-circuited or short-circuited transmission
lines, if the voltages add up to zero, that looks like a short,
and current is at a maximum. If the currents add up to zero,
that looks like an open and the voltage is at a maximum. If
these conditions occur at the source, 100% re-reflection of
the incident reflected wave energy is guaranteed. The Bird
reads equal forward and reflected power all up and down the
feedline.

If an open-circuited 1/2WL of 50 ohm lossless feedline is
connected to a simple class-A source having a series source
impedance of 50 ohms and a voltage source of 141.4v (as in
W7EL's "Food For Thought #1) the steady-state impedance seen
by the source is an open-circuit so the source voltage is
141.4v and the source current is 0 amps. The implication is
that it is like having nothing connected at all but that's
not correct. Measuring the current at the mid-point of that
1/2WL of feedline will prove the feedline is filled with
EM wave energy which must travel at the speed of light.

The Bird will read 100w forward and 100 reflected on the
feedline. An RF current meter at the center of that 1/2WL
of feedline will read 2.828 amps. That's the sum of the
forward current and reflected current in phase, 1.414 amps
in the forward direction and 1.414 amps in the rearward
direction. 1.414^2*50 = 100w for both forward and reflected
powers. The Bird is right. Those powers are really there
supporting the forward and reflected waves and cannot be
used for any other purpose. Since the feedline is lossless,
there's no lost energy to replace so the source power output
is zero. Anything else would violate the conservation of
energy principle. Note that at the above current maximum
point, the net flow of energy is zero since the Poynting
vectors for forward and reflected power add up to zero.
--
73, Cecil http://www.qsl.net/w5dxp

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