Wes,

As a starter, look at this site:

http://www.cbtricks.com/~ab7if/coax/coax.htm

When a transmission line is terminated in it's characteristic impedance there is
no voltage or current reflection from the line. The electromagnetic fields
continue to flow into the termination as if the line were infinitely long. When
a mismatch of impedance occurs, reflected waves will be produced and they will
interact with the incident waves. The total voltage and current on the line are
no longer the result of a single traveling wave from the source to the load.
Instead, it is the algebraic sum of two waves traveling in opposite directions.
This interaction results in what is known as standing waves. The waves remain in
fixed positions along the line while they vary in amplitude and polarity. A wave
of any shape can be transmitted along the line without any change of waveshape
or magnitude. Looking at the gif below, we see a line driven with a sine wave
generator, terminated with a short circuit to maximize the reflection.

My first claim is a tuner at the source does not materially improve what is
happening in the coax. That is a tuner does not recreate the condition above
where the coax is functioning as a properly matched and terminated transmission
line. All the tuner does is match the impedance at the coax source back to some
known, usually 50 Ohm, value.

My second claim is when the mismatch condition at the coax destination, i.e.
antenna that may result in significant radiation from the coax itself.

Dan

Wes Stewart wrote:
On Sat, 27 Aug 2005 16:53:39 -0700, dansawyeror
wrote:


Let's take the case of a 50 Ohm line and some mismatched antenna. The result is
a combination other then 50 Ohm with most likely a zero complex component.


Surely you don't believe this do you? It is -much- more likely that
the impedance is reactive than not. At one (fundamental) frequency
the reactance is zero. At every other frequency it is reactive.


All a
tuner does is match 50 Ohm at the radio to the complex impedance presented to it
at the source of the line.


Isn't that enough?


That the only place with 50 Ohms and zero inductance in the line - antenna
system. The combination of cable and antenna presents something other then R =
50 ohms 0 reactance and the the transmission line see discontinuities. The
result is it radiates.


Oh dear me.