On Wed, 01 Aug 2007 11:44:12 -0000, Harry7 wrote:

Both of these designs are of the Balanced L or Double L variety. Both
require a balun at the input to convert the 50 ohm unbalanced output
of the transmitter to the balanced tuner & feedline. You still haven't
gotten away from the main cause of inefficiency & power loss which is
the balun. [see http://www.somis.org/bbat.f1.jpg]

These double L tuners can be a PITA to build & use also. You need two
identical inductances at all times in the circuit. This requires
either some mechanical means of driving two identical roller inductors
simultaneously (so that the inductance in each leg always matches) or
two identical switched inductors with exactly the same tap points.

The link coupled design of the Matchbox takes the balun (and it's
potential for power loss) out of the circuit. They are also much
simpler designs, easier to homebrew & tune.

Terry
W8EJO

I wonder if you have built a balanced L tuner? I made mine using only
hand tools and a drill press and had no problems. Also why do you say
they are a PITA to use? I adjust mine using only two knobs - the same
number of adustments I use on my Matchbox. Yes, I have both tuners.

Also, just how much of that terrible inefficiency and power loss does
that balun have? In the link you gave the balun consisted of nothing
more than a length of coax. There would be even less loss using a W2DU
type balun in that it requires a shorter length of coax.

Additionally, my balance tuner will give a 1:1 match on all the HF
bands (and anything in between) - something the Johnson Matchbox will
not do.

So are you talking from experience or just hear say?

Danny, K6MHE