"Dee Flint" wrote in
:


My main HF rig and my husband's main HF rig both have built in tuners.
Both work pretty well. However they do not have the range of
outboard tuners.

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 lot of commericial and military equipment have built in tuners with
quite significant tuning ranges. Of course this comes at a price so
amateur gear doesn't have as much range in their tuning capacity on
the built in tuners.

Size can be an issue too. The IC 761's tuner is a pretty tiny
thing. I had to take an IC 765's autotuner 9 (very similar) apart once to
repair it, and it was around the size of one of the mfj tiny tuners.

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

- 73 de Mike KB3EIA -

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

wrote:


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.

True enough.

snip



You can read AG6K's article he

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

and judge for yourself.

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.


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.

Some day I'll report on how mine is doing. In the present situation I
don't need remote tuning, but will probably motorize the unit anyway.

- 73 de Mike KB3EIA -

On Mar 6, 4:30?pm, Michael Coslo wrote:
wrote:

You can read AG6K's article he

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

and judge for yourself.

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.

All you have to do to use it with an unbalanced line is to ground the
coax shield at the tuner end of the coax balun,
and use the "other side" to feed the ungrounded line. A
simple SPST switch of adequate ratings can do the job.

The AG6K tuner, as described, has adequate matching
range for most dipole-fed-with-balanced-line amateur
antennas. A little care in choosing the antenna and
feedline length can make the tuner's job a lot easier.

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

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.

Some day I'll report on how mine is doing. In the present situation I
don't need remote tuning, but will probably motorize the unit anyway.

Although not mentioned in the article, the roller inductors
could be replaced by a pair of tapped coils and a double-pole switch.
The tap positions would have to be found by
experiment, but could be made permanent once they were found. Tuner
adjustment could then consist of simply selecting the correct tap
postion with the switch, and
adjusting the variable capacitor for minimum SWR.

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.

73 de Jim, N2EY

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.



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



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?

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.

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

- 73 de Mike KB3EIA -

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

wrote:
The whole thing is so simple that at first I wondered why it wasn't
more common back then.

Ever watch an ART-13 tune itself?
--
73, Cecil http://www.w5dxp.com

wrote:
[snip]
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.
[snip]

I'm not sure a "balanced" tuner is required. I have an off-center-fed
dipole I use with 600 ohm ladder line, and I'd like to try it with an
Ultimate Transmatch. If I put AG6K's coax balun on the input and isolate
the chasis from ground, wouldn't that achieve the same result?

Bill


--
73,

Bill W1AC

(Remove "73" and change top level domain for direct replies)

Mike Coslo wrote:

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

I wish that the manufacturers would include the provision for balanced
feedline. The random-length dipole, fed with balanced line, is an ideal
antenna in many cases. It's especially appropriate for disaster
situations (and simulated disasters, like Field Day). Find the two
highest supports that are available, as far apart as possible, measure
the distance, cut the wire and install the middle insulator and
feedline, hoist each end, and you're done. Now you've got a reasonably
efficient radiator (especially if there's enough distance between those
two supports) that you can use on any band, and the length of the
feedline isn't particularly critical. But it takes a tuner and balun to
make it work, and if this was included in the rig and was automatic, it
would be ideal.

73, Steve KB9X