A choke balun is what is inserted between the transmitter end of the
antenna feedline and the transmitte tuner. Or it can be inserted at
the antenna end of the line.

Questions : How effective is it? To what extent can the percentage
unbalance current on the feedline be expected to be reduced? Has
anybody ever measured it before and after insertion?
----
Reg.

Reg:

I can comment on my recent experiments with a half-wave vertical on
10-11 meters.

A current balun (or ferrite beads on the coax) greatly reduce feedline
radiation--seems to have an overall beneficial effects on the antennas
radiation pattern--and seems to "stabilize" the pruning/tuning of the
antenna (things begin behaving in a linear and logical way.)

Mind you, the above is only deduced/measured with a FSM, SWR bridge (of
the type which does NOT work for real measurement of swr but rather
transmitter loading) and observed/known signals from other stations and
the reports given back on my signal from these stations.

While this may be viewed as "crude" by some--it is real world in that
the effects as least "seem" real.

Or, the short form of all this is, "The Current Balun is my friend!"

John

"Reg Edwards" wrote in message
...
A choke balun is what is inserted between the transmitter end of the
antenna feedline and the transmitte tuner. Or it can be inserted at
the antenna end of the line.

Questions : How effective is it? To what extent can the percentage
unbalance current on the feedline be expected to be reduced? Has
anybody ever measured it before and after insertion?
----
Reg.

Reg Edwards wrote:
A choke balun is what is inserted between the transmitter end of the
antenna feedline and the transmitte tuner. Or it can be inserted at
the antenna end of the line.

Questions : How effective is it? To what extent can the percentage
unbalance current on the feedline be expected to be reduced? Has
anybody ever measured it before and after insertion?

Yep, and you'll find it right on the web. Go to
http://eznec.com/Amateur/Articles/Baluns.pdf and read the section titled
"Experiments" beginning on p. 3 of the PDF document. You might also find
some other interesting information in this article.

Warning, though. It was written by an American, so should be regarded
with great suspicion and skepticism.

Roy Lewallen, W7EL

On Sun, 26 Jun 2005 13:37:46 +0000 (UTC), "Reg Edwards"
wrote:


Questions : How effective is it? To what extent can the percentage
unbalance current on the feedline be expected to be reduced? Has
anybody ever measured it before and after insertion?

Reg, I haven't measured it, however...

I am in the process of modeling a balun as follow up on my G5RV feed
systems analysis. The scenario is a G5RV at 10m centre height, a
vertical drop of open wire line (the so called "matching section") and
a balun at near ground height (with unbalanced shunt admittance
introduced by the balun to ground).

I have been jiggling the unbalanced shunt admittance introduced by the
balun and observing the current through that admittance wrt the
feedline currents, and the apparent distortion of the radiation
pattern. I could nearly as easily have been comparing the current in
one of the wires of the feedline wrt the other, it is just the format
of the currents report that makes the former easier. Another
interesting observation would be the changes to receive sensitivity to
vertically polarised waves (indicating possible feedline pickup).

The models indicate a few things so far:
- the effect of the balun is on the unbalance current distribution on
the whole feedline;
- current imbalance at the base of the "matching section" of better
than about -15dB caused little distortion of the pattern on 20m and
below;
- some configurations seem quite undesirable in terms of pattern
distortion even though balun current is quite low;
- raising the antenna / feedline / balun and lengthening the earth
connection from the balun shunt admittance changes the current
distribution.

This leads me to think that measurement of the imbalance current at a
single point might not give the "big picture". I found scenarios where
inserting an imperfect balun increased the current at a point (it
changed the magnitude of the standing wave and more importantly moved
the current minimum), so I could see someone with a handy-dandy
current probe measuring such a situation and insisting they have proof
the baluns don't "work".

Owen
--

Owen wrote:
. . .
This leads me to think that measurement of the imbalance current at a
single point might not give the "big picture". I found scenarios where
inserting an imperfect balun increased the current at a point (it
changed the magnitude of the standing wave and more importantly moved
the current minimum), so I could see someone with a handy-dandy
current probe measuring such a situation and insisting they have proof
the baluns don't "work".

This situation lends itself well to modeling, where it's readily
illustrated. While it's often difficult to exactly model a given
physical setup, modeling allows us to control the variables and clearly
see what's happening. We can often apply this knowledge and insight to
real situations.

Roy Lewallen, W7EL

On Mon, 27 Jun 2005 00:33:52 -0700, Roy Lewallen
wrote:

Owen wrote:
. . .
This leads me to think that measurement of the imbalance current at a
single point might not give the "big picture". I found scenarios where
inserting an imperfect balun increased the current at a point (it
changed the magnitude of the standing wave and more importantly moved
the current minimum), so I could see someone with a handy-dandy
current probe measuring such a situation and insisting they have proof
the baluns don't "work".

This situation lends itself well to modeling, where it's readily
illustrated. While it's often difficult to exactly model a given
physical setup, modeling allows us to control the variables and clearly
see what's happening. We can often apply this knowledge and insight to
real situations.


Exactly. Nothing I wrote was intended to comment adversely on your
quoted paper, it is interesting and relevant... just a pity the
results tables are not 100% legible.

Modeling shows me the risks of single point measurement, and I agree
entirely with your final statement "While it's often difficult to
exactly model a given physical setup, modeling allows us to control
the variables and clearly see what's happening. We can often apply
this knowledge and insight to real situations". A whole lot of insight
can be gained in a very short time.

Owen

--

Reg:

As usual, your posts inspire thought--and that is a GOOD thing.

At least with this type of balun:
http://home.datacomm.ch/hb9abx/pactor-e-choke.htm

I ask, "Why not?" The insertion loss is negligible. The downside of
its' use is virtually none. The upside is that in the future, as
objects may come into the field close enough to couple with the antenna,
or corrosion-weather-"stretch"-age-"or other factors begin to cause
slight imbalances-- the balun steps in and begins enforcing a "balance."

It just seems one would error on the side of caution and use such a
balun. I know of few better examples of a "win-win situation."

Indeed, the article Roy offered seems like one heck of an argument to
this end...

.... certainly someone not prepared to weigh the "fly chit" they have
picked out of the pepper should just chuck one in the line and rest
assured "it is a good thing."

Warmest regards,
John

"Reg Edwards" wrote in message
...
A choke balun is what is inserted between the transmitter end of the
antenna feedline and the transmitte tuner. Or it can be inserted at
the antenna end of the line.

Questions : How effective is it? To what extent can the percentage
unbalance current on the feedline be expected to be reduced? Has
anybody ever measured it before and after insertion?
----
Reg.

What impedance ratio are you interested in? Reason for asking is that
when I was looking for prior art on current baluns I came across a very
interesting 1:1 design that uses two equal length pieces of coax that would
each be less than an eighth of a wavelength long and which has a very wide
bandwidth. I copied the schematic (which has a slight error) and the photo
to a single sheet PDF file if anyone's interested.

Chris

,----------------------. High Performance Mixers and
/ What's all this \ Amplifiers for RF Communications
/ extinct stuff, anyhow? /
\ _______,--------------' Chris Trask / N7ZWY
_ |/ Principal Engineer
oo\ Sonoran Radio Research
(__)\ _ P.O. Box 25240
\ \ .' `. Tempe, Arizona 85285-5240
\ \ / \
\ '" \ IEEE Senior Member #40274515
. ( ) \
'-| )__| :. \ Email:
| | | | \ '. http://www.home.earthlink.net/~christrask
c__; c__; '-..'.__

Graphics by Loek Frederiks

"Reg Edwards" wrote in message
...
A choke balun is what is inserted between the transmitter end of the
antenna feedline and the transmitte tuner. Or it can be inserted at
the antenna end of the line.

Questions : How effective is it? To what extent can the percentage
unbalance current on the feedline be expected to be reduced? Has
anybody ever measured it before and after insertion?
----
Reg.

On Mon, 27 Jun 2005 03:41:01 GMT, "Chris Trask"
wrote:

I came across a very
interesting 1:1 design that uses two equal length pieces of coax that would
each be less than an eighth of a wavelength long and which has a very wide
bandwidth. I copied the schematic (which has a slight error) and the photo
to a single sheet PDF file if anyone's interested.

I would be interested. I can leave an address or you can get it from
QRZ.

thanks


--
73 for now
Buck
N4PGW

On Sun, 26 Jun 2005 13:37:46 +0000 (UTC), "Reg Edwards"
wrote:

A choke balun is what is inserted between the transmitter end of the
antenna feedline and the transmitte tuner. Or it can be inserted at
the antenna end of the line.

Questions : How effective is it? To what extent can the percentage
unbalance current on the feedline be expected to be reduced? Has
anybody ever measured it before and after insertion?
----
Reg.


I ran across an article on choke baluns recently in the 2004 ARRL
handbook. It said ( as best as I can recall ) that "purists" might
argue for the use of a choke balun for dipoles for the optimum
radiation pattern, but that most dipoles weren't high enough off the
ground to have a "correct" pattern anyway, so their use for optimum
radiation patterns is questionable at best. Keeping RF out of the
shack might be a different story ? I used a coaxial choke balun on my
G5RV but I don't use either a coaxial choke balun or a commercial
balun on either my 40 meter dipole ( too heavy, the dipole is
constructed out of 18 Ga wire ) or my 30 meter dipole. I was too lazy
to go through all the hassles of either wiring up a PL connector for
the commercial choke balun I have and I didn't want to wind up several
feet of coax for a coaxial balun ( weight and sag issues again )

YMMV

Gary