On Mar 7, 12:01�pm, Michael Coslo wrote:
wrote:
On Mar 6, 4:30?pm, Michael Coslo wrote:
I have gathered the parts to make just that!. I'd have it up now, but I
switched to a coax fed antenna for a while, and built a more traditional
tuner. In the interim I went back to balanced line.

The AG6K tuner can be used with balanced or unbalanced
line.

I should have been more clear about the reasons. The tuner that I made
is a massively retro unit that is kinda pretty. Cherry finished wood
face, with real old time knobs and cranks. If I went to the balanced one
now, I'd need to start over again. I will eventually build the AG6K type
balanced tuner of course, but want to enjoy this one for a while.

Understood.

Reg Edwards' DIPOLE3 program can be a big help in
figuring out the shack-end impedance of various
antenna/transmission line combinations.

* * * * I have all his programs.

Me too. In several places!

Upon his demise, his family and a number of
interested amateurs made sure to archive and distribute them. We miss
Reg over on rraa.

I miss him too. I read his bio somewhere - very impressive.
A real class act.

Although not mentioned in the article, the roller inductors
could be replaced by a pair of tapped coils and a double-pole switch.

* * * * The tuner can be hot switched, I assume?

Depends on the switch, but I would not do that even with
heavy-duty switches. Puts an unnecessary strain on the
rig feeding the tuner.

Automatic tuners are not new to amateur radio, btw.
An automatic balanced tuner was described in QST for July, 1952. It
would automatically retune itself within
an amateur band. Changing bands meant changing coils, but once that
was done the tuner would do the rest automatically.

To be really accurate, such a tuner might best be
called "semi automatic". You had to manually
set it up for each band - it couldn't usually find a
match by blind luck. But once you had the coil and taps
set, it would find a match and follow you up and down the band.

Although the original used a balanced link-coupled tuner, the
principles could be applied to any tuner that meets the
basic concepts.

One modern-day use I can see for such a tuner is for 80/75 meters
with, say, a dipole. You could QSY anywhere in the band and the tuner
would automatically follow.

* * * * Thanks for the reference, Jim. It should be interesting to see how they
did it then.

I looked up the articles. Here's how they did it:

The key to the system is the in-line phase detector. It looks a lot
like the sensing element of an SWR bridge, but what
it senses is the power factor (reactance ratio) of the load.
The phase detector has two DC outputs.

If the load is resistive, the two outputs are equal. If the load is
inductive, one output is higher than the other, and if the load is
capacitive the other output is higher.

The DC outputs are fed into a sort of DC differential amplifier
(couple of 6SN7s) which operate a pair of relays.
The relays control a reversible 2 rpm motor that turns the
big splitstator capacitor in the tuner.

If the two outputs are equal, neither relay energizes and the motor
doesn't run. If the load is capacitive, one relay energizes and turns
the motor one way, and if the load is inductive the other relay
energizes and turns the motor the other way.

No operator attention was needed at all once the system was set up.
You didn't have to push a "TUNE" button or anything else - the tuner
would simply do its thing when you transmitted.

In a later article, the same idea was applied to a mobile
installation, retuning the antenna loading coil automatically.
This was long before "screwdriver" antennas!

The whole thing is so simple that at first I wondered why it wasn't
more common back then. The answer is that most rigs of that era had
lots of adjustments, and automating one
of them didn't really save all that much in most cases. Today, with no-
tune rigs, maybe it's worth another look.

73 de Jim, N2EY