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Old December 25th 07, 11:06 PM posted to rec.radio.amateur.antenna
Roger[_3_] Roger[_3_] is offline
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First recorded activity by RadioBanter: Dec 2007
Posts: 72
Default Standing-Wave Current vs Traveling-Wave Current

Cecil Moore wrote:
Roy Lewallen wrote:

The existence of both voltage and current at any point along the line
tells us that there is instantaneous power at that point, ...


Not if the voltage and current are always 90 degrees out of
phase which is a fact of physics for pure standing waves. There
is no power, instantaneous or otherwise, in pure standing waves.
The cosine of 90 degrees is *always* zero.


These comments in total are very interesting, by both authors. Thank
you for them.

It is clear that there is not a standard way of describing energy that
is in the process of being stored in either an inductor or capacitor.
Clearly it is stored, not used (converted) as in a resistor.

Storage of energy in a capacitor (for instance) occurs over time and
requires power to complete. So how do we describe that power if it is
always zero because voltage and current are 90 degrees out of phase?
Should we recognize that only the peak voltage and peak current is 90
degrees out of phase, with the entire charging time occurring within
those two time extremes? Between those two time extremes, the voltage
and current are in phase but at changing impedance, with power flowing
into the capacitor. So think I.

I think of the "standing wave" as being equivalent to the graph on my
power bill that shows power used daily over a month. Granted that the
standing wave is recorded in V or I, but we only need to know the R that
the standing wave is acting through to determine the power that it
represents.

I certainly find this interesting.

73, Roger, W7WKB