[TenTec] 2A GA Omni A, Omni D at w4rrw

[Gary Bold]

Hi Jules and others,

I think that you are describing the low-pass "LCL" tee, which also works,
and I have used this too.  Nice features are:  It IS a low-pass network,
requires only ONE capacitor, and can indeed act with either inductor
adjusted out to give an L with the inductor at either end - thus arranging for
a larger range of reactances than is obtainable with a standard variable
capacitor.

The design equations are the same for both high-pass and low-pass tee
versions, you just have to calculate the appropriate component values from
the reactances, swapping L for C etc.

There are three reasons I don't use these:  Firstly, it is messy to arange 
tapping
of TWO coils (but quite possible), secondly, there are TWO inductors, and these
are always more lossy than capacitors, thirdly, you need to orient the coils to
minimize inductive coupling between them.   It will still work as a transmatch
even if inductive coupling exists, but may have odd tuning characteristics.

Theory shows that all transmatches are LEAST lossy when the load to be matched
is resistive and close to the nominal input impedance desired.  Losses increase
as the load becomes higher or lower.

The Johnson Matchbox has received high praise over the years.  I have never
used one, and few commercial ones appear to have made their way to ZL land.
However, a number of ZLs use them with balanced lines, and give them high
praise.

Gary ZL1AN

At 07:35 PM 6/30/03 -0400, you wrote:
>Hello Gary, and others.
>I've successfully used a defferent version of the tee tuner, the capacitor
>in the middle going to ground and the inductors, one going to the tx and the
>other going to the antenna.  Adjusting the inductors could make it a "L" net
>to feed high Z or low Z (depending which inductor adjusted out; zero I).
>Adjusting the capacitor, one could load about anything.
>cheers,
>Jules  K8JK