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
.................................................. ..........