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

I'll try to answer that.
Voltage baluns are designed to provide equal voltages on the
outputs, such as those needed for balanced antennas. They help to keep
the balance against external influences, such as nearby metal bodies
and such.
Current balun are used with unbalanced loads, such as windom
antennas, when it's needed to qeep the currents as equal as possible.
This is done in order to minimize radiation from the line, which is
more corrent dependent than voltage dependent.
Choke baluns serve to break the path between the load and the
source so as to prevent energy to flow in a common mode fashion aleng
the line (usually from the load to the source). the name itself-the
full name, that is- " common mode choke" is self explanatory.
Alex 4Z5KS

I'll try to answer that.
Voltage baluns are designed to provide equal voltages on the
outputs, such as those needed for balanced antennas. They help to keep
the balance against external influences, such as nearby metal bodies
and such.
Current balun are used with unbalanced loads, such as windom
antennas, when it's needed to qeep the currents as equal as possible.
This is done in order to minimize radiation from the line, which is
more corrent dependent than voltage dependent.
Choke baluns serve to break the path between the load and the
source so as to prevent energy to flow in a common mode fashion aleng
the line (usually from the load to the source). the name itself-the
full name, that is- " common mode choke" is self explanatory.
Alex 4Z5KS