Gene Fuller, W4SZ wrote:
"The problem comes from the higher losses that occur in even the
"lossless" transmission line when operating at high voltages and
currents."

That`s right. Gene put quotes around "lossless".

The power output of the transmitter equals thaat taken by the load
inspite of hier indicated forward power. The difference is a power that
continues to circulate, much as baggage on an airport carrousel
continues to circulate until it is taken away.

Best regards, Richard Harrison, KB5WZI

So, in Maxwell's words (paraphrased): the signal continues to reflect up
and down the line until it is all finally radiated or lost in the
transmission line. The mismatch at the antenna/line junction doesn't
matter. Most of the loss is in the transmission line and that can be
reduced by using ladder line.

Each reflection transfers what it can and the next one transfers the same
percentage. If 50% gets to the antenna the first time then 50% of 50% or
25% goes the second time and 50% of 25% or 12.5% goes the third time etc etc
until it eventually gets close to a total of 100% transfer. Now this sounds
like calculus and is starting to scare me.

Why doesn't the signal coming back down the line in the reflected portion
cancel out the signal going up the line? And if the up and down part is
out of phase ( as I suspect it would be) why isn't there some kind of
interference resulting in distortion or reduced signal strength?

"Richard Harrison" wrote in message
...
Gene Fuller, W4SZ wrote:
"The problem comes from the higher losses that occur in even the
"lossless" transmission line when operating at high voltages and
currents."

That`s right. Gene put quotes around "lossless".

The power output of the transmitter equals thaat taken by the load
inspite of hier indicated forward power. The difference is a power that
continues to circulate, much as baggage on an airport carrousel
continues to circulate until it is taken away.

Best regards, Richard Harrison, KB5WZI

On Wed, 7 Jan 2004 23:34:50 -0500, "Craig Buck" wrote:

Why doesn't the signal coming back down the line in the reflected portion
cancel out the signal going up the line?

This is what is called the standing wave.

And if the up and down part is
out of phase ( as I suspect it would be) why isn't there some kind of
interference resulting in distortion or reduced signal strength?

Because there is no load (except your meter when you discover it).

73's
Richard Clark, KB7QHC

Craig Buck wrote:
Why doesn't the signal coming back down the line in the reflected portion
cancel out the signal going up the line? And if the up and down part is
out of phase ( as I suspect it would be) why isn't there some kind of
interference resulting in distortion or reduced signal strength?

Signals traveling in opposite directions in a lossless transmission line
do not affect each other except at an impedance discontinuity where
reflections occur. Forward waves and reflected waves are essentially
transparent to each other in a transmission line with a constant
characteristic impedance, and are the two necessary and sufficient
components of the standing wave which is indeed an interference
pattern. Interference can and often does occur without any effect
on the individual EM waves that are involved in the interference.

If the standing waves were visible light instead of RF, one would
see bright spots at the voltage maximums and dark spots at the
voltage minimums. I have learned a lot about transmission lines
from the field of optics.
--
73, Cecil http://www.qsl.net/w5dxp



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