Sal M. Onella wrote:
Does a T tuner cancel some of the reactance of the line in which it is
inserted, thereby effectively shortening the line.
Am I onto something or have I simply launched myself into the eye of
another ****storm?

A single series length of transmission line can only
transform impedances to other values located on the
SWR circle (or spiral) on a Smith Chart. There is
only one low resistance value on that SWR circle
and it is equal to Z0/SWR. For instance, if the
SWR is 9:1 on 450 ohm line, that value is 450/9 =
50 ohms. If the SWR is 4.5:1, that low resistive
value is 450/4.5 = 100 ohms. If the SWR is 18:1,
that low resistive value is 450/18 = 25 ohms. Only
one value of SWR (9:1) on Z0=450 ohm line will
transform the impedance to 50 ohms. Since my
transceiver is happy with any resistive impedance
between 25 ohms and 100 ohms, I am satisfied with
that maximum 50 ohm SWR of 2:1.

An antenna tuner not only can perform the equivalent
of the above transformation but it can also do the
equivalent of a transformation of the resistance
value to 50 ohms for any SWR within the range of
the tuner. So a tuner can transform 25 ohms or 100
ohms to 50 ohms. A tuner has one more dimension of
matching than does a single series transmission line.

Adding a tapped transformer to a variable length
transmission line system gives it that extra dimension.
A second/third section of transmission line in the
form of a stub will also add that extra dimension.

The main function of matching is to stop reflected
energy from reaching the transmitter leaving it no other
available path except back toward the antenna. That
is done by tuning for a Z0-match at the transmitter. A
tuner is only one way of achieving that Z0-match to
50 ohms.
--
73, Cecil http://www.w5dxp.com