Cecil wrote:

But that is not what happens when two waves cancel. For an idea of what
happens, please reference Reflections II, page 23-8,9. If the two voltages
are 180 degrees out of phase and the two currents are 180 degrees out of
phase, neither one of them can double. Calling that a virtual short or
virtual open is incorrect, IMO.

Cecil, this is the error on Reflections that I told you about last week when
you cited the above reference in Reflections. I inadvertantly called the
effect a 'short circuit', while it is actually an open circuit. If a 3rd
edition of Reflections is ever printed this error will be corrected. Now
when two waves interfere with their voltages 180 degrees out of phase, but
with their currents in phase, we have a short circuit. Either of these
conditions occur at the matching stub point, depending on the resistance
component of the load impedance and the distance from the load to the stub
point.

Cecil also wrote:
"What happens to the energy in the two waves that have their voltage and
current amplitudes equal in amplitude and opposite in phase?"

These two waves continue to circulate.

I forgot to say they are traveling in the same direction and that they
are coherent. The two waves disappear from existence. What happens to
the energy they contained?

I thought it was common knowledge that the reflected energy is totally
re-reflected in the forward direction when encountering the open or short
circuit at the matching point.

Walt, W2DU

Walter Maxwell wrote:
I thought it was common knowledge that the reflected energy is totally
re-reflected in the forward direction when encountering the open or short
circuit at the matching point.

The voltages and currents are listed at the Z0-match point in the following
example:
rho=0.5
200W source---50 ohm feedline--+--1/2WL 150 ohm feedline---50 ohm load
Vfwd1=100V-- Vfwd2=200V--
Ifwd1=2A-- Ifwd2=1.333A--
--Vref1=0V --Vref2=100V
--Iref1=0A --Iref2=0.667A

Vref1 = Vfwd1(rho) + Vref2(tau) (this is the same as b1=s11*a1+s12*a2)
0V = 50V at zero deg + 50V at 180 deg i.e. the voltages cancel

Iref1 = Ifwd1(rho) + Iref2(tau)
0A = 1.0A at 180 deg + 1.0A at zero deg i.e. the currents cancel

Through wave cancellation, both the voltage and current go to zero in
the direction of the source. That's like a short for voltage and an
open for current.
--
73, Cecil http://www.qsl.net/w5dxp



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