On Tue, 02 Nov 2010 18:17:10 -0700, Jim Lux
wrote:

Art Unwin wrote:
[snip]

An L network match either RloadRgen or RloadRgen, depending on which
side the shunt element is on.

In autotuners using an L network (e.g. the LDG boxes), they have a relay
that switches the shunt C to either end of the series L.

In autotuners using a Pi network (e.g. the SGC boxes), there's shunt
elements on both ends, so you can match anything (subject to the
component ranges).

So if you have a motorized C and a motorized L, you'd need to add a
relay to switch the configuration to be able to "match anything"

By the way, a L or Pi network cannot match Rgen=Rload, but you can do it
trivially setting both C's to zero and the L to zero. It's not really an
L or Pi (or T) network then, which is why some automated network
calculators choke on it. A real autotuner doesn't care, because it
almost always starts in the "bypass" position anyway.

That is a great post!

I am slowly working towards a motor driven remote T-Match roller
tuner. I intend to use the same algorithm that I use to operate a
manual tuner.
That is to start with the capacitors at center, the inductor at
minimum. Run the inductor down until the minimum SWR and center it
there. Then do the same with the transmitter side capacitor. Finally,
do the same with the antenna side capacitor. The controlling SWR
signal is from the transmitter point.

I am concerned about making the transmitter happy as quick as
possible. I expect that this is not be the optimum match but it will
serve the purpose of making the transmitter happy.

I start with the inductor because the losses are greater there so less
inductance is likely to have lower losses. I had overlooked that I do
try shunting the tuner first.

After having explained that I realize there is probably a better way.
I will try starting with Max transmitter side C, Min Inductor and
Minimum antenna side C.

I think the ideal procedure would be to calculate the needed match,
build it to minimum loss (in the tuner) and switch it in. I will have
to think about that...
John Ferrell W8CCW