Cecil, check this months QST (August 2005) Page 52 - figure 5. It
specifically shows that reflections can totally cancel creating black.


"Cecil Moore" wrote in message
...
Richard Clark wrote:
When the energy available in the first medium, at the second
interface, cannot possibly reflect enough of it to the first
interface; then no amount of superposition of ALL reflections (and
this presumes that the second interface is fully reflecting for these
succeeding multiples, an absurd notion in its own right) can exceed
that available energy.

Yes, this has all been said before, you've found it interesting but
not compelling; and yet no one here has offered any way to boost the
energy to completely cancel the reflection from the first interface.

I have multiple times, Richard. When a 111.1mW wave interferes with
an 87.78mW wave, the result is *NOT* a 23.32mW wave. It's the waves
that interfere, not the power.

111.1mW - 87.78mW = 23.32mW is superposition of powers and is invalid!

Instead of superposing powers, the equation you need to use is the
power interference equation:

Pref1 = P1 + P2 + 2*sqrt(P1*P2)cos(180)

Pref1 = 111.1mW + 87.78mW + 2*sqrt(111.1*87.78)(-1)

Pref1 = 198.88mW - 197.51mW = 1.37mW

Thus after only one internal reflection cycle, the reflected power,
Pref1, is reduced to 1.37mW, not to 23.32mW as you have asserted.

If you will use a transmission line example and deal with voltages, you
will be able to diagnose your mistake. Voltages interfere, watts don't.
Most RF engineers simply do not understand how to deal with powers
associated with component wave interference.
--
73, Cecil http://www.qsl.net/w5dxp


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