In article ,
Dave wrote:

how does the balanced tuner get from the unbalanced output of the amplifier
and the balanced feedline? is there not a balun in there somewhere anyway?

I've seen three approaches used:

- Asymmetrical (unbalanced) tuner of the T or L or pi configuration,
with a balun at the output. This seems to be the most common
configuration, but is often said to suffer from a degraded balance
or unacceptable losses in the balun when feeding high-Z loads.
It's not easy for a balun to provide adequate choking reactance
when feeding such loads.

- Tuners which use a symmetrical T or L configuration, with the input
to the matching network being fed from the rig/amplifier's 50-ohm
output via a balun. An internal W2DU-type "ferrite beads on coax"
balun seems to be popular in such designs.

- Link-coupled tuners, such as the Johnson Matchbox and the newer
Z-match designs. The input side of the circuit operates unbalanced
and is usually asymmetrical, while the output side (the link) is
balanced with respect to ground. The input and output sides are
coupled inductively. There's sometimes a small amount of imbalance
created by capacitive coupling across the link, but this seems to
be small enough to have little practical effect on the quality of
the balance. In this case, the balanced-to-unbalanced function is
performed by the inductive link, and there's no separate "balun"
component.

--
Dave Platt AE6EO
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