I've recently put up a 140' dipole fed with ladderline. My tuner is
separate from my rig, and is an unbalanced unit. So, I use a balun on the
tuner output to hook the ladderline to.

I've been told that I should have a voltage balun in this application. I
was surprised to hear this, as I expected to hear use a current balun.

Is the voltage balun the right one for this application?

RB wrote:

I've recently put up a 140' dipole fed with ladderline. My tuner is
separate from my rig, and is an unbalanced unit. So, I use a balun on the
tuner output to hook the ladderline to.

I've been told that I should have a voltage balun in this application. I
was surprised to hear this, as I expected to hear use a current balun.

Is the voltage balun the right one for this application?

Only if you want your feedline currents to be unbalanced.
Your antenna is a lot like the one described on my web
page below that uses a 1:1 choke-current-balun and needs
no conventional tuner, the most efficient configuration
I could come up with. As can be seen from the current
maximum point graph on my web page, ~100 feet is a good
compromise length for the ladder-line for such an antenna.

A lot of hams will tell you to throw up a random length of
ladder-line and feed it through a 4:1 voltage balun. That's
usually not good advice and often results in a poor balun
function on one or more bands. If one doesn't know approximately
what impedance is being seen by the balun, one cannot predict if
it will function or not. The free version of EZNEC can predict
the approximate impedance seen by the balun. www.eznec.com
--
73, Cecil http://www.qsl.net/w5dxp/notuner.htm

Cec,

As an aside, there appears to be a little confusion about the various
uses of baluns which arises from their uncertain perhaps misleading
descriptions.

Because of the way balun winding-wires are run, they are often
described as transmission line transformers.

There are --

Voltage Baluns, Current Baluns and Choke baluns.

As I see it, Voltage Baluns have a definite voltage/impedance/turns
ratio and are true impedance transformers. They may be used as either
balanced-to-unbalanced windings, or be balanced-to-balanced, or be
unbalanced-to-unbalanced. Balanced windings may be centre-tapped.
One winding may be common to both primary and secondary windings.

Choke Baluns consist of a pair of wires wound together around a
ferrite core. The two wires may be of coaxial form or may consist of
a twisted pair or just a pair of wires laid alongside each other. The
two wires together form a transmission line of calculable impedance
and loss.

But a Choke Balun hss no impedance or voltage ratio. It is incorrect
to refer to it as having an impedance ratio such as 1-to-1.

A Choke Balun does indeed behave as an impedance transformer from one
end of its line to the other. But the transformation ratio is
indeterminate. The ratio depends on frequency and line length as with
any other transmission line.

The effects of inserting a Choke Balun between an unbalanced tuner and
a balanced transmission line to the antenna can be beneficial insofar
as tuner settings are concerned.

But in general, the length of line on a choke balun should not exceed
1/8th or 1/10th of a wavelength at the highest frequency of use. This
is not too difficult to achieve in the HF range of 1.8 or 3.5 to 30
MHz.

But I do not understand what is meant by a Current Balun.

Perhaps Roy, who is very good at it, could define what is a Current
Balun if there is such a thing. And while he is about it, Voltage and
Choke Baluns.

He may choose to give them different names. But his views can only be
beneficial to the mislading waffle which surounds them.
----
Reg.

Reg Edwards wrote:
But a Choke Balun hss no impedance or voltage ratio. It is incorrect
to refer to it as having an impedance ratio such as 1-to-1.
But I do not understand what is meant by a Current Balun.

Reg, the words, "choke" and "current" have become synonymous
when used as an adjective to describe baluns. A choke-balun
*is* a current-balun, usually a 1:1. N:1 current baluns exist
where N is not equal to one. Sometimes, an extra winding on
the toroid ensures that the currents are balanced.

Perhaps Roy, who is very good at it, could define what is a Current
Balun if there is such a thing. And while he is about it, Voltage and
Choke Baluns.

Try: http://www.eznec.com/Amateur/Articles/Baluns.pdf

Also: http://www.w2du.com/r2ch21.pdf

Current baluns balance the feedpoint currents and voltage baluns
balance the feedpoint voltages. Since unbalanced currents cause
radiation from the feedline, current baluns are considered
superior for amateur radio applications. The W2DU choke balun is
a member of the subset of current baluns.
--
73, Cecil http://www.qsl.net/w5dxp

No, a current balun is the desired beasty in this case.

"RB" wrote in message
. ..
I've recently put up a 140' dipole fed with ladderline. My tuner is
separate from my rig, and is an unbalanced unit. So, I use a balun on the
tuner output to hook the ladderline to.

I've been told that I should have a voltage balun in this application. I
was surprised to hear this, as I expected to hear use a current balun.

Is the voltage balun the right one for this application?

A choke (or current) balun is the correct choice.

The input impedance of the transmission line to the antenna varies all
over the shop from one band to another. So there is no definite
impedance to which the transmitter is to be matched.

A voltage balun is designed to match between two definite known
impedances of a given ratio, for example 4-to-1, 300-to-75 ohms,
values which never exist at your particular place in the system.

A choke or current balun is not intended to match one impedance to
another. It is intended only to allow, without loss, the transition
from a balanced line to an unbalanced tuner or transmitter.

Because the choke balun is in fact a short length of transmission line
wound on a ferrite core, an impedance transformation does occur
between one end and the other. But what the antenna line input
impedance is transformed to doesn't matter. It is just another
impedance for the tuner to handle and, as likely as not, the tuner
will handle it just as well. Just a change in L and C settings.
----
Reg, G4FGQ.

Reg Edwards wrote:
A choke or current balun is not intended to match one impedance to
another.

Reg, there are 4:1 current baluns. See Figs A3-3,4 in
Roy's Balun article.
--
73, Cecil http://www.qsl.net/w5dxp

Cec, a choke balun has an indeterminate ratio.

A choke balun which the man asked about, is, as you say, a current
balun.

I don't doubt that there are some forms of current baluns which have a
definite ratio. But they have more than two wires. They can be used to
transform one admittance or susceptance to another. ;o)

One thing for sure - they are all transmission line transformers -
for the want of a better name!

In some ways they are remarkable components. They should have been
invented 100 years before alongside ordinary L,C, R & G. But they had
to wait for the invention of ferrites which I understand did not occur
until the early 1940's in wartime Holland. But I would not be
surprised if somebody comes along with the idea that the invention was
in Bell Labs in the 1930's. Even before the Smith Chart which was an
adaption of similar charts in use in the late Victorian Age.

In the 1950's I met an American engineer who told me that in 1945
there were Americans looking round bombed-out German radio factories
and by chance came across some tiny top hats with narrow brims and
with 3 fine wires sticking out of one end. "What on Earth are these"
they asked.

I could go on. It's the Devil which makes me say such things. ;o)
----
Reg.

You might find it instructive to take a look at
http://eznec.com/Amateur/Articles/Baluns.pdf.

Roy Lewallen, W7EL

RB wrote:
I've recently put up a 140' dipole fed with ladderline. My tuner is
separate from my rig, and is an unbalanced unit. So, I use a balun on the
tuner output to hook the ladderline to.

I've been told that I should have a voltage balun in this application. I
was surprised to hear this, as I expected to hear use a current balun.

Is the voltage balun the right one for this application?

Good replies. Thanks.

So: does the commonly available choke balun (round cylinder with coax
connectors on each end, and ferrite beads inside the cylinder) allow us to
put unbalanced feed in one end, and get balanced feed on the other?

Or, are they ununs?