I'm not sure I would call it an "apparent" match. It's just
that a T network is two L networks back to back. You can
transform up to some impedance and then down to what you are
trying to match. How far you are from the input impedance
with the "intermediate" impedance determines how much more
circulating current you have in the elements (as opposed to
a better match which is just what is necessary and not so
far and away from the input (and output) impedance. There
are many intermediate impedances. Finding the lowest one to
suit the match requirements results in the lowest stored
energy (which is consumed by the elements in the tuner). The
Pi tuner transforms down and then up. Same issues. Lots of
other complications such as canceling reactances, etc., but
this way of thinking about it helps I think.
Having just one L network (has to be reversible) like in the
238B, makes the job simpler. There is just one setting but
you need a larger range of values of C and L to do the job
with just one L network. I mentioned in a previous post that
the losses might be greater in the single L network over a T
if the Q of the element is not very high and a large value
of L (or even C) must be used to obtain a match.
Chuck, KE9UW
---- Original message ----
>Date: Mon, 21 Mar 2005 15:34:59 -0500
>From: "Thomas Jednacz" <tjednacz@ieee.org>
>Subject: Re: [TenTec] tentec 238B or palstar 1500cv ?
>To: "'Discussion of Ten-Tec Equipment'"
<tentec@contesting.com>
>
>Another reason is an L tuner only has one match point. A T
tuner can have an
>apparent match and a real match. In the apparent match
condition all the
>energy is going into the tuner and circulating with nothing
going out the
>feed line. A switchable L tuner (L or C input) can have a
wider match
>impedance range.
>
>Tom, W7QF
>>
>> The L network is more efficient by having losses in only
two
>> components, an L and C vs. 3 components in the
conventional Tee tuner.
>
>>
>
>
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