On Mar 4, 10:23�pm, Mike Coslo wrote:
* * * * I should have noted large range and balanced/unbalanced output. My
IC-761 has an autotuner on it that works pretty well with my vertical
antenna. The dipole is run with balanced line, and needs a different
tuner.

---

* * * * A little bigger components, plus a 4:1 balun, and they would have
it.

Well, sort of.

The Ancient Ones used antenna matching
devices to feed balanced lines. The Johnson
Matchboxes are one example of a commercial
version. Most Handbooks have examples of
link-coupled balanced wide-range tuners.

The problem was that such link-coupled tuners are large
and not easy to bandswitch.

About 1970, a new idea in tuners appeared: Use an
unbalanced matching network such as a T or L
network with a roller inductor or tapped inductor, with a
balun if balanced output was wanted. 4:1 iron-core toroid
baluns were compact and broadband, the T or L tuner
could be made wide-range without complex bandswitching,
and the whole works seemed an improvement on the old
link-coupled balanced tuner.

The problem was that baluns aren't magic devices. The
system works well if the shack-end of the transmission line
is around 200 ohms impedance and not too reactive. But in
many cases the shack-end impedance with balanced line
is very high or very low, and/or very reactive. Under such
conditions the balun may not do a very good job because it is
being asked to work far outside its design parameters.

Also, if the shack-end impedance is low (say, 12 ohms), the
use of a 4:1 balun will make it so low (3 ohms) that it may be outside
the efficient matching range of the T or L network.

These conditions may be partially remedied by use of a balun
that can be switched to either 4:1 or 1:1 ratio, and by choosing
antenna and feedline combinations that don't result in extreme
values of shack-end impedance/reactance. But that reduces
the flexibility of the system.

The "unbalanced tuner followed by a balun" idea is clearly
one where "newer" wasn't necessarily "better" in all cases.
Yet it became very popular because it usually worked.
But in many cases the balanced line was actually
doing a lot of radiating and there was considerable loss in the
system.

Back in 1990, AG6K came up with an answer to the
shortcomings of that method. He put a 1:1 balun between the
rig and a simple balanced tuner, so the balun only has to
deal with a pure 50 ohm load once the tuner is adjusted.
Although AG6K favors baluns made from coax wound on
PVC pipe, other forms of balun such as ferrite-bead and
wound-toroid can be used if preferred.

You can read AG6K's article he

http://www.somis.org/bbat.html

and judge for yourself.

AG6K's approach used two ganged roller inductors and
a single variable capacitor, compared to most commercial
manual tuners that use two variable caps and a single variable
inductor. Because there are only two controls, remoting the
tuner is made easier.

73 de Jim, N2EY