Cebik's material covers a significant amount of design and historical data
for link-coupled tuners. W9CF, W7EL, W8JI and others have shown that
placement of a CM choke at the input of a tuner only offers a benefit when
the tuner is symmetrical. (e.g., AG6K type, and not T, L, nor Pi types).
Specifically, W9CF writes:
"As noted by Roy Lewallen, W7EL, putting a choke balun on the input of an
unbalanced tuner to drive a balanced line is useless. It introduces a
``hot'' tuner case which must be isolated with no benefit over putting the
balun on the output."
Since the traditional link-coupled tuner performs the BAL-UN function across
an air core RF transformer, no CM choke is required. The unbalanced input
side of the tuner is formed by a tapped link, and in some cases, one side of
the link is in series with a variable shunt C to ground.
Cebik's material also discusses similarities and differences between
link-coupled tuners that require the re-tapping of the output coil as well
as the output "voltage divider" tuner (e.g., Johnson Matchbox)
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