antenna tuner
 

I'm looking for plans to build a balanced tuner for ladderline without a
balun. In the past, I've seen schematics for tuners with ganged
inductors. Can't seem to stumble back upon these on a web search. Any
ideas and thanks in advance.

Gary

On Sun, 27 Mar 2005 11:44:58 -0800, Angela & Gary
wrote:



I'm looking for plans to build a balanced tuner for ladderline without a
balun. In the past, I've seen schematics for tuners with ganged
inductors. Can't seem to stumble back upon these on a web search. Any
ideas and thanks in advance.

Gary

See

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

But it still requires a balun. If you wish to use no balun then you'll
need to build a link type tuner.

Danny, K6MHE

In article ,
Angela & Gary wrote:

I'm looking for plans to build a balanced tuner for ladderline without a
balun. In the past, I've seen schematics for tuners with ganged
inductors. Can't seem to stumble back upon these on a web search. Any
ideas and thanks in advance.

You'll need some form of inductively coupled ("link-coupled") tuner to
do this. The most popular of these at the moment seems to be the
"Z-match" - it has good although not perfect current balance on the
outputs.

Most of the Z-match designs I've seen can be implemented with two
variable capacitors, and one fixed inductor. There's a "two coil"
Z-match but I gather that it doesn't really have advantages over the
one-coil variety. The coils can be either air-wound, or wound on a
powdered-metal toroid.

--
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!

There are a few balanced tuners available for purchase. I assume you
just want the building experience? If not, Johnson Matchbox tuners are
sometimes available on Ebay and other sites. And MFJ has two current
models. And Palstar has one current balanced tuner.

Good luck, jimbo

Angela & Gary wrote:
I'm looking for plans to build a balanced tuner for ladderline
without a
balun. In the past, I've seen schematics for tuners with ganged
inductors. Can't seem to stumble back upon these on a web search.
Any
ideas and thanks in advance.

Gary

You'll need a balun whether or not you use a balanced tuner.

That is unless you have a balanced transmitter.

You can save yourself the cost of a pair of ganged inductors by
inserting a choke balun between the balanced feedline and an ordinary
unbalanced tuner.
----
Reg

In article ,
Reg Edwards g4fgq,regp@ZZZbtinternet,com wrote:

You'll need a balun whether or not you use a balanced tuner.

That is unless you have a balanced transmitter.

.... or a link-coupled tuner, which works just fine without a balun
(or, looked at in another way, incorporates a balun as part of its
basic design).

You can save yourself the cost of a pair of ganged inductors by
inserting a choke balun between the balanced feedline and an ordinary
unbalanced tuner.

.... and being very careful to "float" the chassis of the tuner clear
of ground, and insulate it thoroughly.. If you don't do this, your
ground connection bypasses the choke balun, and/or you can be "bitten"
by the RF on the chassis which will often be at a substantial
potential above ground.

--
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!

The whole purpose of the choke balun is to allow the ordinary tuner to
be safely grounded.

The tuner is grounded automatically by virtue of its short connection
to the unbalanced transmitter.

Or have I misunderstood you?
----
Reg

In article ,
Reg Edwards g4fgq,regp@ZZZbtinternet,com wrote:

The whole purpose of the choke balun is to allow the ordinary tuner to
be safely grounded.

The tuner is grounded automatically by virtue of its short connection
to the unbalanced transmitter.

Or have I misunderstood you?

It depends. There are two arrangements using choke baluns that I'm
aware of - balun at the input, and balun at the output.

It's fairly common to put a choke balun at the output of an unbalanced
tuner, to convert the unbalanced output to a balanced form. This
seems to work pretty well when the tuner is looking into loads that
aren't too high, low, or reactive in nature. For high-R or
highly-reactive loads, it may be difficult to create a choke balun
with a high enough choking reactivity to force adequate balance on the
line. In this approach, the tuner can be connected to the transceiver
via a direct cable, and its chassis can be connected to the station RF
ground.

The other approach is to put a choke balun at the input of the tuner,
"float" the tuner chassis clear of ground, and connect the balanced
line directly to the "unbalanced" output of the tuner. This
pseudo-balanced arrangment can provide good balance once the tuner is
adjusted, because the balun "sees" 50 ohms on both sides... but it
adds the complication of having to float and insulate the tuner. I've
heard of some people taking a commercial tuner, and putting it on
insulators inside a secondary outer chassis. The outer chassis can be
connected to the station ground, and or to the transceiver coaxial
feedline braid _before_ going through the choke balun.

--
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!

Dave Platt wrote:
In article ,
Reg Edwards g4fgq,regp@ZZZbtinternet,com wrote:


The whole purpose of the choke balun is to allow the ordinary tuner to
be safely grounded.

The tuner is grounded automatically by virtue of its short connection
to the unbalanced transmitter.

Or have I misunderstood you?


It depends. There are two arrangements using choke baluns that I'm
aware of - balun at the input, and balun at the output.

It's fairly common to put a choke balun at the output of an unbalanced
tuner, to convert the unbalanced output to a balanced form. This
seems to work pretty well when the tuner is looking into loads that
aren't too high, low, or reactive in nature. For high-R or
highly-reactive loads, it may be difficult to create a choke balun
with a high enough choking reactivity to force adequate balance on the
line. In this approach, the tuner can be connected to the transceiver
via a direct cable, and its chassis can be connected to the station RF
ground.

The other approach is to put a choke balun at the input of the tuner,
"float" the tuner chassis clear of ground, and connect the balanced
line directly to the "unbalanced" output of the tuner. This
pseudo-balanced arrangment can provide good balance once the tuner is
adjusted, because the balun "sees" 50 ohms on both sides... but it
adds the complication of having to float and insulate the tuner. I've
heard of some people taking a commercial tuner, and putting it on
insulators inside a secondary outer chassis. The outer chassis can be
connected to the station ground, and or to the transceiver coaxial
feedline braid _before_ going through the choke balun.

Hi Dave and all,

For Reg. I've used the method that Dave speaks of above over the years
with very good Sucess but as he says the tuner must be isolated from
ground in order to produce the needed balance at the out put. The
advatage as stated is that the Balun (once the turner is tuned to the
frequency being used will see pretty much 50 ohms on both sides. It has
work very well here .

73 Dave Kc1di

Angela & Gary wrote:
I'm looking for plans to build a balanced tuner for ladderline without a
balun. In the past, I've seen schematics for tuners with ganged
inductors. Can't seem to stumble back upon these on a web search. Any
ideas and thanks in advance.

Gary
Hi Gary,

you may find the following web sites of interest in designing your own
balanced tuner.
hope they help in your quest.
73 Dave KC1DI

http://www.cebik.com/link/link.html

http://www.cebik.com/edu/edu6.html

http://www.cebik.com/link/l-bal.html

another approach is the Z-Match tuner

http://www.qsl.net/wb3gck/zmatch.htm

http://www4.tpgi.com.au/users/ldbutl...CoilZMatch.htm

(Note it is very desirable on the Z-Match to have Vernier dials as the
Adjustments can be very sharp and easy to miss without them.)

http://www.seboldt.net/k0jd/z-match.html#schematic

Dave Platt wrote:
... or a link-coupled tuner, which works just fine without a balun

How efficient is link-coupling? I have an old
Sunair PN-099400 auto-tuner that uses motor-
driven variable-link coupling. Too bad it runs
on 28 vdc.
--
73, Cecil http://www.qsl.net/w5dxp

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Dave Platt wrote:
The other approach is to put a choke balun at the input of the tuner,
"float" the tuner chassis clear of ground, and connect the balanced
line directly to the "unbalanced" output of the tuner. This
pseudo-balanced arrangment can provide good balance once the tuner is
adjusted, because the balun "sees" 50 ohms on both sides... but it
adds the complication of having to float and insulate the tuner.

There's considerable debate on that configuration. If we assume
the common-mode current doesn't change when we move the choke
from output to input, i.e. it is a systematic problem, then the
choke is exposed to exactly the same common-mode current on output
and input. Common mode current travels on the tuner chassis and the
coax shield input and coax shield output may be one inch from each
other with a dead short between them.

And here's something that no one, to the best of my knowledge,
has mentioned. If one succeeds in balancing the currents at
the input of an unbalanced antenna tuner, the currents at the
output will automatically be unbalanced because the current on
the coax center wire will suffer a greater phase delay than
the current on the coax inner braid thus forcing some current
to the outside of the coax. This effect should be easy to measure.

Link coupling solves the common-mode problem. Unfortunately, the
MFJ balanced tuners do not relieve the stress on the choke. Take
a look at the schematic to see why.
--
73, Cecil http://www.qsl.net/w5dxp

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... or a link-coupled tuner, which works just fine without a balun

How efficient is link-coupling? I have an old
Sunair PN-099400 auto-tuner that uses motor-
driven variable-link coupling. Too bad it runs
on 28 vdc.

I'm not sure that there's any single answer to that question.

Comments on eHam.net from owners of the old Johnson (or Nye) Matchbox
link-coupled tuner seem to suggest that it's capable of operating with
low losses - significantly lower than are achieved by some of the
unbalanced T-configuration tuners mentioned.

I suspect that the efficiency depends very much on the design and
implementation of the tuner (e.g. air-core coils vs. a toroidal
design, size of core, degree of coupling between the tank and the
link, wire gauge) and on the specific impedance being matched.

Based on what I've read about Z-match tuner design, it seems that
close coupling across the inductive link helps boost the efficiency.
However, the close inductive coupling tends to come with an increased
amount of capacitive coupling, and this can apparently affect the
output balance for the worse in some cases.

I suspect (but don't know for sure) that link-coupled designs which
use a fixed-position, tightly-coupled link (e.g. an air-wound or
toroid-core Z-match) may be more efficient than those which use a
"swinging" link with variable coupling.

--
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!

You'll still need a balun even with a balanced tuner.

Save yourself the expense of a pair of ganged roller coasters.

Reg Edwards wrote:
You'll still need a balun even with a balanced tuner.

If it's link-coupled, like the Johnson Matchboxes, the
link performs the cancellation of the common-mode current.
--
73, Cecil http://www.qsl.net/w5dxp


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