How do I test a choke balun?
 

How can I test how well a choke balun is performing? I know how to test a
transformer balun, but am cluless as how I can compare several different
choke balun approaches.

How can I test how well a choke balun is performing? I know how to test a
transformer balun, but am cluless as how I can compare several different
choke balun approaches.

One possible method comes to mind... use an RF current probe to see
how much RF is actually flowing on the outside of your feedline. I've
seen plans for such probes, made from a clamp-on ferrite choke core
and winding (making a simple RF transformer) plus a diode, cap, and
meter.

In order to distinguish conducted RF (which the balun would be
expected to be able to stop) from induced RF from the antenna itself
(which would probably go right around the balun) you might want to
try disconnecting the antenna itself from the output of the balun, and
substituting an equivalent resistance/reactance at the frequency of
interest. Push a few watts into the "dummy load", run the current
probe down the feedline from the balun to your rig, and see what the
peak current is. Repeat at multiple frequencies, and (if practical)
with different feedline lengths. Using a half-wavelength-long coaxial
feedline would probably maximize the sensitivity of the test, as it
would present a low RF impedance on the outside of the coax at the
"bottom" of the current balun.

Repeat with other current baluns and compare.

To be complete, I suppose that you'd also want to measure the
temperature of each balun before and after a high-power test, to try
to get some feeling for the amount of loss in the balun itself.

--
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!

"Fred W4JLE" wrote in message
...
How can I test how well a choke balun is performing? I know how to test a
transformer balun, but am cluless as how I can compare several different
choke balun approaches.

Fred

I dont have the skills nor knowledge to tell you how to test the choke
balun. I do have some experience with testing of my home made choke
baluns.
I made connection to the shield of the coax that is surrounded by the
"choke balun", and measured the impedance across it. My reasoning was that
the major objective of the balun was to present a high impedance to current
along the outside of the coax.
It occurres to me that my reasoning might be invalid, since it seems too
obvious, and you already know the "impedance" test isnt adequet.

Jerry

Fred:

With a toroid core, using the manufacturers data on uh/mh per number of
turns, al factor and such, should allow you to compute the inductance and
come to a value of the impedance that inductance poses at the operating
freq(s) in question...

Major problem I see is a resonance(s) occurring with feedline length and
the inductance chosen, but even that could be designed out with a pencil
and paper... the physical testing you are inquiring about has my interest
also...

John

On Mon, 22 Aug 2005 19:08:43 -0400, Fred W4JLE wrote:

How can I test how well a choke balun is performing? I know how to test a
transformer balun, but am cluless as how I can compare several different
choke balun approaches.

Fred W4JLE wrote:
How can I test how well a choke balun is performing? I know how to test a
transformer balun, but am cluless as how I can compare several different
choke balun approaches.


You can measure the impedance by shorting the input conductors together
and the output conductors together. Then connect the input conductors to
one terminal of an impedance measuring device such as an antenna
analyzer or impedance bridge, and the output conductors to the other
terminal. An impedance of around 500 - 1000 ohms is generally adequate.

If you want to measure its effectiveness in place, you can construct a
current probe like the one shown in Fig. 12 of
http://www.eznec.com/Amateur/Articles/Baluns.pdf. It'll give you a
quantitative measure of the feedline current. You can use a snap-on
split core for convenience. The value at the choke should be very low,
but it might increase considerably about a quarter wavelength down the
line due to induced common mode current. The solution to that is to
insert another choke balun at that point.

Roy Lewallen, W7EL

Fred W4JLE wrote:
How can I test how well a choke balun is performing? I know how to test a
transformer balun, but am cluless as how I can compare several different
choke balun approaches.

I have a toroidal pick-up coil slipped over my coax in the
shack to monitor the magnitude of common-mode currents.
That tells me how chokes, etc., are performing.
--
73, Cecil http://www.qsl.net/w5dxp

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Fred W4JLE wrote:
How can I test how well a choke balun is performing? I know how to test a
transformer balun, but am cluless as how I can compare several different
choke balun approaches.

Hi Fred, If you have an MFJ antenna analyzer it is easy. You have
to measure the choking Impedance at the frequency of interest. Rule of
thumb is 10X the transmission line or Antenna Impedance, depending on
where the the balun is located. 50 ohm impedance, 500 ohm choke
impedance.
The 259 manual has a section on testing baluns. You can download the
manual from MFJ.
Gary N4AST

Fred:

As my last post gave away, my chokes are constructed on math and
observation in practical work... (well, prayer too grin)

I see roy is recommending 10x the impedance of the feedline (coax?) for
the choke/balun, minimum (I am guessing here a bit), he obviously knows
what he is speaking about, however, at 160m when you are struck with the
physical dimensions of the choke/balun needed--well, at those times I have
accepted a 5:1 ratio of choke/balun impedance to feedline impedance...

.... but then, I am here to learn ...

John


On Mon, 22 Aug 2005 19:08:43 -0400, Fred W4JLE wrote:

How can I test how well a choke balun is performing? I know how to test a
transformer balun, but am cluless as how I can compare several different
choke balun approaches.

Thanks to all for the information. Roy I particularly wanted to thank you
for the copy of your article from the antenna compendium.

I appreciate all the input from others as well. I was planning to do a
number of tests with ferrite beads and air coil baluns.

The data accumulated will be presented here for all to peruse. Thanks again
guys!

On Mon, 22 Aug 2005 17:19:29 -0700, John Smith
wrote:

Fred:

As my last post gave away, my chokes are constructed on math and
observation in practical work... (well, prayer too grin)

I see roy is recommending 10x the impedance of the feedline (coax?) for
the choke/balun, minimum (I am guessing here a bit), he obviously knows
what he is speaking about, however, at 160m when you are struck with the
physical dimensions of the choke/balun needed--well, at those times I have
accepted a 5:1 ratio of choke/balun impedance to feedline impedance...

... but then, I am here to learn ...

John


On Mon, 22 Aug 2005 19:08:43 -0400, Fred W4JLE wrote:

How can I test how well a choke balun is performing? I know how to test a
transformer balun, but am cluless as how I can compare several different
choke balun approaches.

Fred, Roy's method is fine, but here's the second way I perform the
test with baluns constructed with ferrite beads surrounding a
transmission line. However, it does require two baluns.

To begin we connect the two baluns back-to-back, i.e. connect the
output of the first to the output of the second, and loading the
normally unbalanced input terminals of the second balun (now the
output) with a 50-ohm resistor.

Next, feed a signal into the input of the first balun and measure the
voltage between the outer surface of the line feeding the input of the
first balun and the outer surface of the unbalanced input terminals at
the output of the second balun. In the ideal balun the voltage between
these two points would be zero.

Next, disconnect the connections between the two baluns, and reconnect
them, reversing the connections. Now repeat the voltage measurement
between the same points as in the previous measurements.

In the ideal balun the voltage now measured will also be zero.

However, with a real balun, the voltage between the two points
specified will usually be zero when the connection between the two
baluns is such that the outer conductors and inner conductors of both
baluns are directly connected, respectively.

But the real test of the baluns comes when the outer conductor of the
first balun is connected to the inner conductor of the second balun,
and the outer conductor of the first balun is connected to the inner
conductor the second balun. The lower the voltage obtained in this
condition, the better the balun. With a perfect balun the voltage will
again be zero, but if the effect of the balun is zero the voltgage
measured across the specified point will equal the input voltage.

The ratio of the voltage at the input of the balun to the voltage
appearing at the points specified above is twice the ratio of the
forward voltage to the common mode voltage that would appear on the
outside surface of the feed line when that balun is used in practice.

Walt, W2DU

Thank you Walt, my interest is both ferrite bead baluns and coax air core. I
have searched the internet and found a lot of measurements of magnitude and
phase angles for various configurations, unfortunately none of them appear
to agree. I am hoping to come up with a definitive set of tables that the
average guy can use.

The only things I know for sure is that no balun covers from DC to daylight,
or even 1.8 to 30 Mhz.

I was thinking it might be solved with washers and steel wool. (Grin)


"Walter Maxwell" wrote in message
...
On Mon, 22 Aug 2005 17:19:29 -0700, John Smith
wrote:

Fred:

As my last post gave away, my chokes are constructed on math and
observation in practical work... (well, prayer too grin)

I see roy is recommending 10x the impedance of the feedline (coax?) for
the choke/balun, minimum (I am guessing here a bit), he obviously knows
what he is speaking about, however, at 160m when you are struck with the
physical dimensions of the choke/balun needed--well, at those times I
have
accepted a 5:1 ratio of choke/balun impedance to feedline impedance...

... but then, I am here to learn ...

John


On Mon, 22 Aug 2005 19:08:43 -0400, Fred W4JLE wrote:

How can I test how well a choke balun is performing? I know how to test
a
transformer balun, but am cluless as how I can compare several
different
choke balun approaches.

Fred, Roy's method is fine, but here's the second way I perform the
test with baluns constructed with ferrite beads surrounding a
transmission line. However, it does require two baluns.

To begin we connect the two baluns back-to-back, i.e. connect the
output of the first to the output of the second, and loading the
normally unbalanced input terminals of the second balun (now the
output) with a 50-ohm resistor.

Next, feed a signal into the input of the first balun and measure the
voltage between the outer surface of the line feeding the input of the
first balun and the outer surface of the unbalanced input terminals at
the output of the second balun. In the ideal balun the voltage between
these two points would be zero.

Next, disconnect the connections between the two baluns, and reconnect
them, reversing the connections. Now repeat the voltage measurement
between the same points as in the previous measurements.

In the ideal balun the voltage now measured will also be zero.

However, with a real balun, the voltage between the two points
specified will usually be zero when the connection between the two
baluns is such that the outer conductors and inner conductors of both
baluns are directly connected, respectively.

But the real test of the baluns comes when the outer conductor of the
first balun is connected to the inner conductor of the second balun,
and the outer conductor of the first balun is connected to the inner
conductor the second balun. The lower the voltage obtained in this
condition, the better the balun. With a perfect balun the voltage will
again be zero, but if the effect of the balun is zero the voltgage
measured across the specified point will equal the input voltage.

The ratio of the voltage at the input of the balun to the voltage
appearing at the points specified above is twice the ratio of the
forward voltage to the common mode voltage that would appear on the
outside surface of the feed line when that balun is used in practice.

Walt, W2DU

On Tue, 23 Aug 2005 12:03:56 -0400, "Fred W4JLE"
wrote:

Thank you Walt, my interest is both ferrite bead baluns and coax air core. I
have searched the internet and found a lot of measurements of magnitude and
phase angles for various configurations, unfortunately none of them appear
to agree. I am hoping to come up with a definitive set of tables that the
average guy can use.

The only things I know for sure is that no balun covers from DC to daylight,
or even 1.8 to 30 Mhz.

I was thinking it might be solved with washers and steel wool. (Grin)

Well, Fred, go ahead and try the washers, I've already proved that
steel wool doesn't work. (haw)

Walt

The only things I know for sure is that no balun covers from DC to
daylight,
or even 1.8 to 30 Mhz.

==============================
Fred, I'm afraid you're wrong.

Slide a sufficient number of ferrite beads over the coax line and it
will easily cover 1.8 to 30 MHz. Alternatively, wind sufficient turns
around a largish ferrite ring of the correct grade of material.
----
Reg.

On Tue, 23 Aug 2005 16:58:14 +0000 (UTC), "Reg Edwards"
wrote:

The only things I know for sure is that no balun covers from DC to
daylight,
or even 1.8 to 30 Mhz.

==============================
Fred, I'm afraid you're wrong.

Slide a sufficient number of ferrite beads over the coax line and it
will easily cover 1.8 to 30 MHz. Alternatively, wind sufficient turns
around a largish ferrite ring of the correct grade of material.
----
Reg.

Reg is right, Fred, the W2DU balun with 50 #73 beads was designed to
cover from 1.8 - 30 MHz. The series impedance along the outer
conductor of the coax at 2.0 MHz is just over 750 ohms. If the antenna
operating at 2.0 MHz is a half-wave dipole, half the dipole impedance
at resonance will be around 35 ohms. The ratio 750/35 = 21.4, which
gives an approximate isolation of the common-mode current of 26.6 dB
below the current into half the dipole, which is more than adequate.
If you want still more, make the balun with more than the original 50
beadss.

If you don't have a copy of Reflections you can find the balun data
from my web page at www.w2du.com. See Chapter 21, page 21-8, for the
graph that plots the resistance, reactance, and impedance of the
outside surface of the coax in the W2DU balun vs frequency.

Walt, W2DU

At some point a resonance will occur Reg. And while some particular
combination may work - i.e. 7,427 ferrite beads along 841 feet of coax. I
have found no practical balun that does the deed from 1.8 to 30.

Those that work well at 1.8 seem to end up with a resonance somewhere over
20 Mhz..

One solution may be ferrites to cover the low end in series with a solenoid
coil for the high end.

Again, what I am looking for is a simple chart that says for a 10, 15, and
20 meter beam a solenoid of 8 turns on a 4 1/2" pvc coil form will provide
the following impedances ...

Also most people will tell you that just looping the coils together will
cause problems because of capacitance. I don't see that as a bad thing.
Again I need to see data to confirm or discount my assumptions.

If nothing else it will be a fun learning exercise.

I ran into some problems with an all band no tuner antenna and started to
try various combinations of beads recommended by the Gurus. While it worked
OK on 160, 75 and 40, at 15 and10 meters the beads has insufficient
impedance.

Ergo, I have mounted my steed and wooden lance in hand am off to fight the
evil forces of unbalance.

"Reg Edwards" wrote in message
...
The only things I know for sure is that no balun covers from DC to
daylight,
or even 1.8 to 30 Mhz.

==============================
Fred, I'm afraid you're wrong.

Slide a sufficient number of ferrite beads over the coax line and it
will easily cover 1.8 to 30 MHz. Alternatively, wind sufficient turns
around a largish ferrite ring of the correct grade of material.
----
Reg.

Walt, not to take a thing away from your W2DU balun. I suspect you have
never characterized it at high power.

The #73 material gets really hot at higher power.

"Walter Maxwell" wrote in message
...
On Tue, 23 Aug 2005 16:58:14 +0000 (UTC), "Reg Edwards"
wrote:

The only things I know for sure is that no balun covers from DC to
daylight,
or even 1.8 to 30 Mhz.

==============================
Fred, I'm afraid you're wrong.

Slide a sufficient number of ferrite beads over the coax line and it
will easily cover 1.8 to 30 MHz. Alternatively, wind sufficient turns
around a largish ferrite ring of the correct grade of material.
----
Reg.

Reg is right, Fred, the W2DU balun with 50 #73 beads was designed to
cover from 1.8 - 30 MHz. The series impedance along the outer
conductor of the coax at 2.0 MHz is just over 750 ohms. If the antenna
operating at 2.0 MHz is a half-wave dipole, half the dipole impedance
at resonance will be around 35 ohms. The ratio 750/35 = 21.4, which
gives an approximate isolation of the common-mode current of 26.6 dB
below the current into half the dipole, which is more than adequate.
If you want still more, make the balun with more than the original 50
beadss.

If you don't have a copy of Reflections you can find the balun data
from my web page at www.w2du.com. See Chapter 21, page 21-8, for the
graph that plots the resistance, reactance, and impedance of the
outside surface of the coax in the W2DU balun vs frequency.

Walt, W2DU

In article ,
Fred W4JLE wrote:

Again, what I am looking for is a simple chart that says for a 10, 15, and
20 meter beam a solenoid of 8 turns on a 4 1/2" pvc coil form will provide
the following impedances ...

http://www.bcdxc.org/balun_information.htm#Ed,%20WA2SRQ has some of
that sort of information, for a few specific combinations of turns,
diameter, and winding style.

Also most people will tell you that just looping the coils together will
cause problems because of capacitance. I don't see that as a bad thing.
Again I need to see data to confirm or discount my assumptions.

What I have heard is that scramble-winding the turns tends to create a
higher distributed capacitance, and lowers the frequency at which the
balun exhibits self-resonance.

This appears to be born out by the table in the URL I gave above.
Compare the "8 turns, 6-5/8" columns for single-layer and bunched
windings. The single-layer coil has its peak impedance at 12 MHz.
The bunched-turn coil peaks somewhere between 6 and 7 MHz (highest
displayed impedance is at 6 but the phase is still very positive, so
I'm inferring a higher-impedance peak between 6 and 7 MHz).

The impedance of the bunched-turn coil seems to drop faster, on either
side of resonance, than that of the solenoid-would coil.

This suggests to me that the bunched-turn coil, measured and trimmed
carefully, might be a convenient choice for a low-HF monoband
antenna's choke, since it'd need fewer turns of coax to achieve a high
choking impedance. The solenoid-wound coil appears to have a somewhat
broader effective frequency range, and thus might be a better choice
for a 10/15/20 tribander.

--
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!

Fred W4JLE wrote:
At some point a resonance will occur Reg. And while some particular
combination may work - i.e. 7,427 ferrite beads along 841 feet of coax. I
have found no practical balun that does the deed from 1.8 to 30.

Those that work well at 1.8 seem to end up with a resonance somewhere over
20 Mhz..
. . .

You're using the wrong kind of ferrite. Type 43, the most common type
used for large cores, has a Q of 1 in the middle of the HF range. That
is, the resistance equals the reactance at that frequency. So over the
HF range a balun wound on a type 43 core with no air gap or by using
beads W2DU-style looks basically like a resistor. You'd have to have
extremely sensitive equipment to detect any resonance effects.

70 series ferrites have an even lower frequency Q=1 point, along with
more impedance per turn squared, and that's what I mostly use. But a
balun made with type 70 can sometimes get uncomfortably hot if you're
running a kW.

Roy Lewallen, W7EL

Walter Maxwell wrote:

snip
Walt, W2DU

Thank you for that, Walter. This one gets printed and goes in the binder.

tom
K0TAR

For the performance/behaviour of a solenoid-wound coaxial choke,
download program SELFRES from website below.

Enter dimensions of the coil and the resonant frequency and impedance
versus frequency in a test circuit is calculated.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

The performance of a coaxial choke inserted at the antenna end of the
feedline cannot be properly studied without knowledge of the
feedline's length in wavelengths and how the feedline is terminated at
the transmitter end. No two systems are the same.

Choke performance depends on the condition of the system before the
choke is inserted. The choking effect depends on the impedance seen
by the choke looking into the outer conductor of the coaxial feedline.

The input impedance of the coaxial outer conductor depends on Zo, 400
to 550 ohms, of the single-wire line, its length in wavelengths, and
on the very uncertain resistance of the ground connection at the
transmitter end.

If the ground connection at the transmitter end is very low and the
line is an odd number of 1/4-wavelengths there will be a very high
impedance at the antenna end and longitudinal current will negligible.
Insertion of the choke will have no effect.

If the line is a whole number of 1/2-wavelengths, with a low
resistance ground the input impedance of the coaxial outer conductor
will also be very low and longitudinal current in the line will be at
a maximum. Insertion of the choke will be very effective.

With the usual random line length and on different bands, choke
performance will always be completely random and unpredictable. Which
explains the different opinions and arguments about whether a choke is
necessary or not.

Program SELFRES3 models choke behaviour.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

On Tue, 23 Aug 2005 18:17:23 -0500, Tom Ring
wrote:

Walter Maxwell wrote:

snip
Walt, W2DU

Thank you for that, Walter. This one gets printed and goes in the binder.

tom
K0TAR

I'm pleased that you find my data useful, Tom,

Walt

Reg Edwards wrote:
If the line is a whole number of 1/2-wavelengths, with a low
resistance ground the input impedance of the coaxial outer conductor
will also be very low and longitudinal current in the line will be at
a maximum. Insertion of the choke will be very effective.

To complicate things a little more, the common-mode current may
consist of standing waves. If the choke is installed at a current
minimum point, it may have little effect.
--
73, Cecil http://www.qsl.net/w5dxp

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"Cecil Moore" wrote in message
...
Reg Edwards wrote:
If the line is a whole number of 1/2-wavelengths, with a low
resistance ground the input impedance of the coaxial outer
conductor
will also be very low and longitudinal current in the line will be
at
a maximum. Insertion of the choke will be very effective.

To complicate things a little more, the common-mode current may
consist of standing waves. If the choke is installed at a current
minimum point, it may have little effect.
--
73, Cecil http://www.qsl.net/w5dxp
====================================

Dear Cec, It doesn't complicate things. It merely repeats what I have
already said. When the line is an odd number of 1/4-waves long and
there is an (albeit indeterminate) ground at the transmitter end, then
there will be a high impedance at the choke (DUE TO STANDING WAVES)
and the choke will then be wasting its time.

If you havn't, moons ago, already downloaded the program then do so
and read the program notes. There are so many unknowns in it the
results are only approximate but nevertheless sufficiently accurate
for the intended purpose - which is just to demonstrate choke
behaviour.

The only accurate result is the calculated-from-first-principles
self-capacitance of the coil on which the impedance/frequency response
depends.

I had checked calculations, years back, by winding many coils of
various sizes and shapes, (one 7 feet long), with various numbers of
turns and measuring the coils' self-resonant frequency over the HF
band using hand-held instruments with coils suspended in free space
from strings. I always knew the results would be useful at some time
or other, never even dreaming about choke baluns.

Did I ever tell you that for several years I was Head of a
Measurements Standards Laboratory which I personally set up from
scratch and which was in the 2nd echelon from the British National
Physical Laboratory. The NPL.

There were certain electrical parameters for which the laboratory was
capable of making measurements more accurate than the NPL but for
obvious political reasons it was not possible for the laboratory to
claim such performance on calibration certificates.

Some time after I had left the position on promotion, the wicked Mrs
Thatcher had the laboratory dismantled and sold it off in bits because
it did not produce any immediate, short-term profits. She was a
chemist who went into politics. Often I still wonder what happened to
the oven-enclosed battery of 12 standard Western cells.

One day, if I can force myself to find the time, I may write my
memoirs. I could tell you some amusing stories.
----
Yours, Reg, G4FGQ

Reg Edwards wrote:
When the line is an odd number of 1/4-waves long and
there is an (albeit indeterminate) ground at the transmitter end, then
there will be a high impedance at the choke (DUE TO STANDING WAVES)
and the choke will then be wasting its time.

And what I am saying is that exactly the same thing can happen NO
MATTER WHAT THE LENGTH OF THE FEEDLINE if the choke is located at
a current minimum point. I'm not arguing with you - just expanding
upon what you said.
--
73, Cecil http://www.qsl.net/w5dxp

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Speaking of useful data, what is the status of reflections III Sir?

"Walter Maxwell" wrote in message
...
On Tue, 23 Aug 2005 18:17:23 -0500, Tom Ring
I'm pleased that you find my data useful, Tom,

Walt

On Wed, 24 Aug 2005 16:01:06 +0000 (UTC), "Reg Edwards"
wrote:


One day, if I can force myself to find the time, I may write my
memoirs. I could tell you some amusing stories.
----
Yours, Reg, G4FGQ


Please force yourself, Reg, we'd all like to hear those stories. And
they should be published for all to read.

Walt

On Wed, 24 Aug 2005 13:49:21 -0400, "Fred W4JLE"
wrote:

Speaking of useful data, what is the status of reflections III Sir?

"Walter Maxwell" wrote in message
.. .
On Tue, 23 Aug 2005 18:17:23 -0500, Tom Ring
I'm pleased that you find my data useful, Tom,

Walt

Hi Fred,

Reflections 3 is at the publisher. I don't know the current status,
but thanks for asking. I'll keep the rraa up to date at it progresses.
It'll also be announced on my web page at w2du.com.

Walt