Clark,
Maybe the Ultimate and SPC were not forerunners of the T but I never saw
a T until after that Murch Ultimate came out. Other manufacturers came
out with the T, which was less costly to produce and worked as well at
matching a wide range of impedances as the Ultimate did. I, like you,
had a Murch and converted it to the SPC circuit. I felt however that the
SPC arrangement was a bit too touchy to adjust.
If someone has information of a T network tuner sold commercially prior
to the Murch Ultimate it would be interesting to know what it was. I
don't remember any, but then sometimes I forget which exit to take off Rt
95 when I'm driving home in the evening!
As to harmonic attenuation, that's hardly a concern these days as most
rigs are quite adequate in this area. A PI or series inductor L are both
loss pass in nature and would be better than a T or an Ultimate which are
both high pass types. The SPC is basically an Ultimate with that third
cap relocated to give more of a band pass rather than high pass effect.
I really prefer the reversible L that Ten Tec uses. I've never seen a
comparison of this type of tuner with a T as to losses but I'd suspect an
L would be better as it has one less component. I also like the fact that
there is only one setting that will give a match with an L. A T, an
Ultimate and an SPC will match with any number of settings. Some
settings are better that others as to Q and power loss. I can never
remember whether I should have used the setting with the most capacitance
or most inducatnce, etc. With an L you just set it and go!
I'm sure you're right about the PI networks in the old tube rigs. I just
pulled some numbers out of the air. My DX 20 would load power into
everything from a light bulb, to a window screen to a short piece of wire
lying on the floor. It even worked quite well on an off-center fed
dipole I had fed with 75 ohm twin lead.
73,
Puck, W4PM
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