In article E6tvd.6659$7p.4476@lakeread02,
Jack Painter wrote:

I can't imagine what's possibly gained by 1:1 in front of the tuner v. 4:1
(when applicable, some antennas recommend this, including for twin-lead)
after it.

The reason I've seen stated, is that many 4:1 balun designs only work
"as advertised" if they're working into something fairly close to
their design impedances. For example, a 4:1 balun intended to match
200 ohms to 50 ohms, will only provide a 4:1 ratio and good current
balance and efficiency when matching impedances fairly close to those.

If you put such a balun at the output of a wide-range transmatch, and
try to match up a difficult load, then the balun might "see" something
like 750-j250 or 25+10j on its "200-ohm" side. The result might be
poor current balance on the "balanced" side, or excessively high
current flows which would require de-rating the balun's power handling
capability. "Voltage" baluns seem to be most vulnerable to this sort
of problem.

Putting a 1:1 balun on the input side of the tuner, and using a
fully-balanced or pseudo-balanced tuner is one way around this, since
the balun "sees" only the impedance load for which it was designed.

Another approach, often suggested, is to use a 1:1 transmission-line
current balun on the output.

Using a link-coupled tuner (a classic Matchbox, or a Z-match) is yet
another option.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!