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Old June 18th 10, 02:43 PM posted to rec.radio.amateur.antenna
lu6etj lu6etj is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 143
Default Where does it go? (mismatched power)

On 18 jun, 07:55, K1TTT wrote:
On Jun 17, 10:55*pm, Cecil Moore wrote:

On Jun 17, 5:08*pm, K1TTT wrote:


but you have already admitted that it is the only mechanism... though
you will now undoubtedly argue against yourself. * em wave reflection
IS the only mechanism for redistributing rf energy, you admitted that
when you agreed that superposition of the waves is the mechanism that
causes the interference in the first place.


Superposition and reflection are NOT the same mechanism. You are


i didn't say they were

totally confused about what I have said. Wave REFLECTION (of one wave)
is not caused by SUPERPOSITION (of two waves) and vice versa. Wave
reflection happens to a single wave when it encounters an impedance
discontinuity. Superposition requires two or more waves. They are
clearly two completely different mechanisms. So I will repeat what I
said befo


There are two mechanisms for redistributing the reflected energy back
toward the load.


1. The re-reflection of the SINGLE reflected wave from the load at an
impedance discontinuity associated with the power reflection


its really the voltage and current reflection coefficient.

coefficient, e.g. 0.5 in my earlier example. Thus in that earlier
example, 1/2 of the reflected energy from the load is re-reflected
back toward the load and joins the forward wave toward the load. That
leaves 1/2 of the reflected energy that is transmitted through the
impedance discontinuity toward the source without being reflected.


The second energy redistribution mechanism occurs associated with
superposition of MULTIPLE WAVES.


that is what i said, and what you agreed to earlier.



2. The percentage of the reflected energy from the load that is
transmitted through the impedance discontinuity toward the source
superposes with the reflection of the source forward wave from the
impedance discontinuity. In my earlier example, the following two
wavefronts superpose in the direction of the source.


Pfor1(rho^2) = 50w and Pref2(1-rho^2) = 50w


Pref1 = 50w + 50w - 2*SQRT(50w*50w) = 0


This is the second mechanism (wave cancellation) that redistributes


but that is NOT a "second' mechanism. *it IS superposition, which is
what you agreed to earlier, maybe in a different thread. *the
mechanism is superposition, the observation is that the waves
interfere either constructively or destructively.

the energy in the canceled wavefronts back toward the load. This step
2 is technically NOT a reflection since it involves two waves. This is
the step that the RF gurus are missing.


no we are not, we understand superposition which is the underlying
basic mechanism of your optical interference terms.







I really wish you understood the s-parameter equations which are
easier to discuss than the above RF equations.


In the s-parameter equation:


b2 = s21*a1 + s22*a2


the term, s22*a2, is the SINGLE WAVE re-reflection term, i.e. a2 is
the reflected voltage from the load.


In the other s-parameter equation:


b1 = s11*a1 + s12*a2 = 0


s11*a1 and s12*a2 are the TWO WAVEFRONTS that superpose to zero, i.e.


stop there and you are perfectly correct.



engage in wave cancellation.
--
73, Cecil, w5dxp.com- Ocultar texto de la cita -


- Mostrar texto de la cita -- Ocultar texto de la cita -

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the mechanism is superposition, the observation is that
the waves interfere either constructively or destructively.


In the end you will see you basically agree and 90% of this issue it
is the Babel curse :)