I found a 50 year old pencil drawn schematic that was done by an Collins
Radio engineer. So....anyone ever use a coax balun as described below?

Wind a 3.5 inch diameter with 7 turns of RG-58. Space the turns such that
the coil is 4 inches long.
Connect the output of an antenna tuner to one of the balanced feedline
conductors. At one end of the coax coil connect the braid to the antenna
tuner output, and the center connector of the coax to ground.

The other end of the coiled coax: connect the center conductor to the other
balanced feedline conductor. Connect the braid at that end of the coil to
ground.

Comments?

-Wayne
W5GIE
/6

On Wed, 10 Aug 2011 16:50:13 -0700, "Wayne"
wrote:

I found a 50 year old pencil drawn schematic that was done by an Collins
Radio engineer. So....anyone ever use a coax balun as described below?

Wind a 3.5 inch diameter with 7 turns of RG-58. Space the turns such that
the coil is 4 inches long.
Connect the output of an antenna tuner to one of the balanced feedline
conductors. At one end of the coax coil connect the braid to the antenna
tuner output, and the center connector of the coax to ground.

The other end of the coiled coax: connect the center conductor to the other
balanced feedline conductor. Connect the braid at that end of the coil to
ground.

Comments?

-Wayne
W5GIE
/6


Sounds like a pipe-dream.

It would make more sense if two coax baluns were used, symmetrically.

73's
Richard Clark, KB7QHC

In article ,
Wayne wrote:

I found a 50 year old pencil drawn schematic that was done by an Collins
Radio engineer. So....anyone ever use a coax balun as described below?

Many people have. It's also often referred to as a "common mode choke".

One nice characteristic of them is that they don't contain ferrite or
iron cores which could saturate (and create distortion and harmonics)
at high RF current levels.

Wind a 3.5 inch diameter with 7 turns of RG-58. Space the turns such that
the coil is 4 inches long.
Connect the output of an antenna tuner to one of the balanced feedline
conductors. At one end of the coax coil connect the braid to the antenna
tuner output, and the center connector of the coax to ground.

I'm not sure why he specified hooking the braid to the tuner output
and the center conductor to ground. Most people do it the other way
around (it's easier to connect to a PL-259 that way).

Doing it his way brings the "hot" side of the tuner output out closer
to where one might touch it... there may be more of a risk of a shock
or flashover-to-ground situation here, if the SWR on the line is high
and the tuner is looking into a high impedance at the input of the
choke.

This may not be an issue in your particular deployment.

The other end of the coiled coax: connect the center conductor to the other
balanced feedline conductor. Connect the braid at that end of the coil to
ground.

Comments?

http://www.hamuniverse.com/balun.html shows numerous variations on
this same basic idea, and there are about a zillion others out there
on the Net and in the literature.

There are numerous variations:

- Single-layer solenoid-wound (as in the one you described), either
close-wound or spaced.

- Multiple-layer solenoid-wound.

- Scramble-wound.

Different winding style will give different amounts of inductance, and
different (sometimes very different) amounts of distributed
capacitance.

If I understand the situation correctly, a winding style with low
distributed capacitance (e.g. single-layer solenoid-wound with space
turns) functions primarily as a common-mode inductive choke... fairly
broad-band, *if* you have enough turns to give you the necessary
amount of common-mode inductance.

A choke which is multi-layer (perhaps even scramble-wound) can have
more distributed capacitance, and it can act as a parallel-resonant
trap at certain frequencies... giving a nice, high choking impedance
at those frequencies. Above and below that resonance, though, its
impedance can drop off fairly rapidly, and it may not choke the line
effectively. Coaxial chokes of this sort are (I believe) often wound
to give optimal performance on one or two bands.

[I could well be wrong about these details... it's been a while
since I looked at this subject in any detail.]

--
Dave Platt AE6EO
Friends of 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!

"Wayne" wrote in
:

I found a 50 year old pencil drawn schematic that was done by an
Collins Radio engineer. So....anyone ever use a coax balun as
described below?

Wind a 3.5 inch diameter with 7 turns of RG-58. Space the turns such
that the coil is 4 inches long.
Connect the output of an antenna tuner to one of the balanced feedline
conductors. At one end of the coax coil connect the braid to the
antenna tuner output, and the center connector of the coax to ground.

The other end of the coiled coax: connect the center conductor to the
other balanced feedline conductor. Connect the braid at that end of
the coil to ground.

Comments?


Wayne, the device as you describe it is a form of balun (being a device
that facilitates a transition between states of balance).

Considering the ATU output terminal to have voltage V, V is applied
directly to one feedline conductor, and if the common mode impedance of
the coaxial choke is sufficiently high and its length sufficiently
short, approximately -V to the other conductor... so it implements a 1:4
impedance transformation.

The problem is with the "sufficiently" qualifications above. The common
mode impedance of a coil of coax like this has been well explored, it
has a very high impedance over a narrow range near resonance, and
mediocre to low away from resonance, and so not well suited to broadband
use.

Nevertheless, these types of things have appeal to those who are
prejudiced against ferrite, or who just do things on the cheap.

I hasten to add that I have used just such a coil of coax as a single
band 1:1 current balun, but it was carefully resonated for the band in
use, and it measured much higher common mode impedance than practical
ferrite cored baluns.

Mentioning current baluns, you describe a balun that could not be
categorised as an effective current balun, as if you were to ground the
side of the load direct connected to the ATU, the whole thing fails.

I know that to many there is a magic to all things that came from
Collins, but you don't see this widely done, and for good reason.

Owen

"Owen Duffy" wrote in message
...

"Wayne" wrote in
:

I found a 50 year old pencil drawn schematic that was done by an
Collins Radio engineer. So....anyone ever use a coax balun as
described below?

Wind a 3.5 inch diameter with 7 turns of RG-58. Space the turns such
that the coil is 4 inches long.
Connect the output of an antenna tuner to one of the balanced feedline
conductors. At one end of the coax coil connect the braid to the
antenna tuner output, and the center connector of the coax to ground.

The other end of the coiled coax: connect the center conductor to the
other balanced feedline conductor. Connect the braid at that end of
the coil to ground.

Comments?


Wayne, the device as you describe it is a form of balun (being a device
that facilitates a transition between states of balance).

Considering the ATU output terminal to have voltage V, V is applied
directly to one feedline conductor, and if the common mode impedance of
the coaxial choke is sufficiently high and its length sufficiently
short, approximately -V to the other conductor... so it implements a 1:4
impedance transformation.

The problem is with the "sufficiently" qualifications above. The common
mode impedance of a coil of coax like this has been well explored, it
has a very high impedance over a narrow range near resonance, and
mediocre to low away from resonance, and so not well suited to broadband
use.

Nevertheless, these types of things have appeal to those who are
prejudiced against ferrite, or who just do things on the cheap.

I hasten to add that I have used just such a coil of coax as a single
band 1:1 current balun, but it was carefully resonated for the band in
use, and it measured much higher common mode impedance than practical
ferrite cored baluns.

Mentioning current baluns, you describe a balun that could not be
categorised as an effective current balun, as if you were to ground the
side of the load direct connected to the ATU, the whole thing fails.

I know that to many there is a magic to all things that came from
Collins, but you don't see this widely done, and for good reason.

Owen
*******************
Thanks for the comments Owen. I was curious about the schematic, but tend
to stick with my "on hand" ferrite baluns.
--Wayne

"Owen Duffy" wrote in message
...

"Wayne" wrote in
:

I found a 50 year old pencil drawn schematic that was done by an
Collins Radio engineer. So....anyone ever use a coax balun as
described below?

Wind a 3.5 inch diameter with 7 turns of RG-58. Space the turns such
that the coil is 4 inches long.
Connect the output of an antenna tuner to one of the balanced feedline
conductors. At one end of the coax coil connect the braid to the
antenna tuner output, and the center connector of the coax to ground.

The other end of the coiled coax: connect the center conductor to the
other balanced feedline conductor. Connect the braid at that end of
the coil to ground.

Comments?


Wayne, the device as you describe it is a form of balun (being a device
that facilitates a transition between states of balance).

Considering the ATU output terminal to have voltage V, V is applied
directly to one feedline conductor, and if the common mode impedance of
the coaxial choke is sufficiently high and its length sufficiently
short, approximately -V to the other conductor... so it implements a 1:4
impedance transformation.

The problem is with the "sufficiently" qualifications above. The common
mode impedance of a coil of coax like this has been well explored, it
has a very high impedance over a narrow range near resonance, and
mediocre to low away from resonance, and so not well suited to broadband
use.

Nevertheless, these types of things have appeal to those who are
prejudiced against ferrite, or who just do things on the cheap.

I hasten to add that I have used just such a coil of coax as a single
band 1:1 current balun, but it was carefully resonated for the band in
use, and it measured much higher common mode impedance than practical
ferrite cored baluns.
-
Along the lines of trying to understand this, would it be possible to use
the
same circuit with the coil of coax replaced by a 1/4 wave length of open
wire line?


Mentioning current baluns, you describe a balun that could not be
categorised as an effective current balun, as if you were to ground the
side of the load direct connected to the ATU, the whole thing fails.

-
Could you state this a different way, as I don't follow the grounded
output reference.

snip

thanks
Wayne

"Wayne" wrote in
:

"Owen Duffy" wrote in message
...

....

Mentioning current baluns, you describe a balun that could not be
categorised as an effective current balun, as if you were to ground
the side of the load direct connected to the ATU, the whole thing
fails.

-
Could you state this a different way, as I don't follow the grounded
output reference.

I have written some notes about baluns in antenna systems at
http://www.vk1od.net/balun/concept/cm/index.htm . The notes explain why
a current balun is most suited to 'general purpose' antenna application.

In an ideal current balun, the current in each output wire should be
independent of whether one terminal or the other is grounded.

In the case of the balun describe, grounding one or other output
terminal has a large effect on output current in each of the wires.

Proponents of some balun designs insist that they work perfectly into an
isolated load. Of course, it the load is truly isolated, ie there is not
current path to ground from the load, then they are correct, but you
don't need a balun in that case because since the load is properly
represented by a two terminal network, the current into one terminal
MUST equal the current out of the other terminal. Problem is that real
antennas aren't necessarily will represented by a two terminal network
(though we often talk as if they are).

Owen