I am trying to construct a broadband 4:1 balun, and I want to double
check if my understanding of the measurements is correct before I apply
any real RF power.

I do not have access to an antenna analyzer, though I do have an HP4193A
Vector Impedance meter and HP8753 Network Analyzer at my disposal.

First I wound the core in a bifilar manner with the leads being labeled
A1,B1 and A2,B2. Then I measured the input impedance across A1 and A2
leaving B1 and B2 unconnected. Then placed a 200 ohm resistor across A1
and B2 while tying B1 and A2 together, and measured across A1 and A2
looking for 50 ohms (4:1).

I have also seen a reference to a K value for an indication of
broadbandness. K = 1 - L(short)/L(open)

Here are my results...

8 bifilar turns of teflon coated AWG 16, on Type 43 core.

Mhz A1-A2 Open Impedance A1-A2 200 ohm Impedance
2 941 @ +59.5 51.4 @ 3.6 (51.3 +3.2j)
4 2080 @ -25.6 51.7 @ 3.2
7 4130 @ -74.2 52.1 @ 3.7
10 2900 @ -81.5 52.3 @ 4.4
14 1687 @ -84.8 52.4 @ 5.6
18 1180 @ -86.1 52.5 @ 6.8
21 966 @ -86.7 52.6 @ 7.7
25 781 @ -87.2 52.7 @ 9.1
28 682 @ -87.3 52.6 @ 10.2
30 630 @ -87.5 52.7 @ 10.8 (51.7 +9.9j)
-------------------------------------------------------------
50 356 @ -87.0 52.8 @ 18.6
54 327 @ -86.2 52.8 @ 20.4 (49.5 +18j)

Inductance Open = .93 uH
Inductance Short = 167 uH
K == .994

I did not intend to operate this balun above 10m, but thought it would be
interesting to see the 6m data as well. And it looks like it would work
fine there as well.

From what I have read, the open reactance should be at least 4 to 5 times
as high as the normal drive impedence. In this case, it is over 12
times the 50 ohm input at 30Mhz and over 6 times at 54Mhz.

So did I do good? Am I way off?
How can I tell if/when core saturation will be a problem?

--Teh

On Fri, 4 May 2007 09:49:48 +0000 (UTC), Tehrasha Darkon
wrote:

First I wound the core in a bifilar manner with the leads being labeled
A1,B1 and A2,B2. Then I measured the input impedance across A1 and A2
leaving B1 and B2 unconnected. Then placed a 200 ohm resistor across A1
and B2 while tying B1 and A2 together, and measured across A1 and A2
looking for 50 ohms (4:1).

I have also seen a reference to a K value for an indication of
broadbandness. K = 1 - L(short)/L(open)

Here are my results...

8 bifilar turns of teflon coated AWG 16, on Type 43 core.

Hi Teh,

Your numbers suggest Type 75 instead, OR some other mechanism at work.
Given your lead description above is fine, but could have been poorly
implemented (in text, it is difficult to sort those things out).

From what I have read, the open reactance should be at least 4 to 5 times
as high as the normal drive impedence. In this case, it is over 12
times the 50 ohm input at 30Mhz and over 6 times at 54Mhz.

So did I do good? Am I way off?
How can I tell if/when core saturation will be a problem?

The ratio is as good as any. More important is how much power the
BalUn can withstand. Your last question gets into the common
misconception of "core saturation" which is typically a consideration
for the winding linked magnetics not found in this application. BalUns
are not classical power transformers that are so common to 60Hz AC.

The choke BalUn (which is what you are building) employs the lossy
resistance of Ferrite to establish the isolation you want in a BalUn.
There may be some reactance achieved along the way, but it is not
usually a design goal and these class of Ferrites would be a poor
choice in achieving that. If you note that your data describes a
very, very broad curve; it demonstrates a very poor Q which is its
principle attraction (broadbandedness).

As a simple test, pass one very short wire through one bead and
measure its Z (give us a complete description of resistance AND
reactance) over frequency. This will confirm what type material you
are using and will remove unnecessary complexity. Type 43 should show
a frequency peak roughly ten times above your current data's frequency
peak.

73's
Richard Clark, KB7QHC

On Fri, 04 May 2007 09:33:59 -0700, Richard Clark
wrote:

Type 43 should show
a frequency peak roughly ten times above your current data's frequency
peak.

This may have been obscure. The peak of isolation (as revealed in
common mode resistance) should occur in the low VHF region, not the
low HF.

73's
Richard Clark, KB7QHC

On Fri, 4 May 2007 09:49:48 +0000 (UTC), Tehrasha Darkon
wrote:

I am trying to construct a broadband 4:1 balun, and I want to double
check if my understanding of the measurements is correct before I apply
any real RF power.

I do not have access to an antenna analyzer, though I do have an HP4193A
Vector Impedance meter and HP8753 Network Analyzer at my disposal.

First I wound the core in a bifilar manner with the leads being labeled
A1,B1 and A2,B2. Then I measured the input impedance across A1 and A2
leaving B1 and B2 unconnected. Then placed a 200 ohm resistor across A1
and B2 while tying B1 and A2 together, and measured across A1 and A2
looking for 50 ohms (4:1).

I have also seen a reference to a K value for an indication of
broadbandness. K = 1 - L(short)/L(open)

Here are my results...

8 bifilar turns of teflon coated AWG 16, on Type 43 core.

Mhz A1-A2 Open Impedance A1-A2 200 ohm Impedance
2 941 @ +59.5 51.4 @ 3.6 (51.3 +3.2j)
4 2080 @ -25.6 51.7 @ 3.2
7 4130 @ -74.2 52.1 @ 3.7
10 2900 @ -81.5 52.3 @ 4.4
14 1687 @ -84.8 52.4 @ 5.6
18 1180 @ -86.1 52.5 @ 6.8
21 966 @ -86.7 52.6 @ 7.7
25 781 @ -87.2 52.7 @ 9.1
28 682 @ -87.3 52.6 @ 10.2
30 630 @ -87.5 52.7 @ 10.8 (51.7 +9.9j)
-------------------------------------------------------------
50 356 @ -87.0 52.8 @ 18.6
54 327 @ -86.2 52.8 @ 20.4 (49.5 +18j)

Inductance Open = .93 uH
Inductance Short = 167 uH
K == .994

I did not intend to operate this balun above 10m, but thought it would be
interesting to see the 6m data as well. And it looks like it would work
fine there as well.

From what I have read, the open reactance should be at least 4 to 5 times
as high as the normal drive impedence. In this case, it is over 12
times the 50 ohm input at 30Mhz and over 6 times at 54Mhz.

So did I do good? Am I way off?
How can I tell if/when core saturation will be a problem?

--Teh




As you have a vector impedance meter have you measured the common mode
(blocking) impedance? From the description your balun is a voltage
balun that are notorious for having poor common mode impedances.

Danny, K6MHE

On Sat, 05 May 2007 06:29:25 -0700, Danny Richardson wrote:

As you have a vector impedance meter have you measured the common mode
(blocking) impedance? From the description your balun is a voltage balun
that are notorious for having poor common mode impedances.

Danny, K6MHE

Yes, the balun is a 4:1 voltage type. I have not measured the common
mode inductance yet. But in this case, the application is for a Carolina
Windom which requires common mode current to make part of the feedline
act as a radiator.

The feedline will be choked with a 1:1 current balun at the proper
distance. That is next on the list to be built.

--Teh

On Sat, 5 May 2007 19:13:18 +0000 (UTC), Tehrasha Darkon
wrote:

Yes, the balun is a 4:1 voltage type.

Hi Teh,

Then, yes, you certainly have to worry about core saturation and
failure.

73's
Richard Clark, KB7QHC

On Sat, 5 May 2007 19:13:18 +0000 (UTC), Tehrasha Darkon
wrote:

Yes, the balun is a 4:1 voltage type. I have not measured the common
mode inductance yet. But in this case, the application is for a Carolina
Windom which requires common mode current to make part of the feedline
act as a radiator.

The feedline will be choked with a 1:1 current balun at the proper
distance. That is next on the list to be built.

--Teh

Okay, then in that case be sure to check the common mode impedance on
your current balun. Many are less than 1K and, for good operation
you'll need more than that. The higher the better.

Danny, K6MHE

On Fri, 04 May 2007 09:33:59 -0700, Richard Clark wrote:

As a simple test, pass one very short wire through one bead and measure
its Z (give us a complete description of resistance AND reactance) over
frequency. This will confirm what type material you are using and will
remove unnecessary complexity. Type 43 should show a frequency peak
roughly ten times above your current data's frequency peak.

73's
Richard Clark, KB7QHC


I did find out that part of my test setup was flawed.
My adapter from the VIM probe to the coil did very naughty things.
The new setup completely isolates the balun from any surrounding
influences and stray L/C is minimized.

Testing the bead material properties.
The beads I am using are supposed to be Type 43, DigiKey #240-2119-ND
aka Steward 28B1250-000. They are .875" high, 1.25" OD and .75" ID.

Using piece of wire 3" long bent into a U shape. Measurements are
Magnitude and Angle of the vector.

Freq.
(MHz) Bare Wire Single Bead Two Beads
..5 .58 @ 29.0 4.62 @ 68.2 9.0 @ 70.3
1 .74 @ 46.0 8.09 @ 70.2 15.8 @ 71.0
2 1.15 @ 62.1 14.36 @ 70.2 28.0 @ 70.4
4 2.08 @ 74.7 25.30 @ 67.0 49.6 @ 66.3
8 4.04 @ 81.8 42.00 @ 61.6 81.7 @ 60.3
16 8.01 @ 85.5 68.50 @ 56.4 132.7 @ 54.0
32 15.93 @ 87.3 105.40 @ 46.9 204.0 @ 42.3
64 31.80 @ 88.4 145.10 @ 37.4 279.0 @ 27.9
110 56.30 @ 89.0 181.00 @ 30.6 333.0 @ 13.2


Remeasuring the Balun.
With the new setup, there is not a big difference in the terminated
measurements, but the peak in the open impedance of the primary winding
went from ~7 Mhz up to 11.4 Mhz.


Freq.
(MHz) Open Inductance 200 Ohm Termination
..5 275 @ 74 49.6 @ 9.2
1 491 @ 72 51.1 @ 5.4
2 897 @ 69 51.8 @ 3.8
4 1731 @ 59 52.0 @ 3.4
8 3710 @ 31 52.4 @ 4.4
16 3460 @ -51 52.6 @ 7.2
32 1261 @ -78 51.9 @ 14.4
64 591 @ -84 51.2 @ 35.7
110 291 @ -83 86.8 @ 76.7

Peak 11.4 Mhz 4850 @ -9.0

--Teh

On Sat, 5 May 2007 20:00:42 +0000 (UTC), Tehrasha Darkon
wrote:

On Fri, 04 May 2007 09:33:59 -0700, Richard Clark wrote:

As a simple test, pass one very short wire through one bead and measure
its Z (give us a complete description of resistance AND reactance) over
frequency. This will confirm what type material you are using and will
remove unnecessary complexity. Type 43 should show a frequency peak
roughly ten times above your current data's frequency peak.

73's
Richard Clark, KB7QHC


I did find out that part of my test setup was flawed.
My adapter from the VIM probe to the coil did very naughty things.
The new setup completely isolates the balun from any surrounding
influences and stray L/C is minimized.

Testing the bead material properties.
The beads I am using are supposed to be Type 43, DigiKey #240-2119-ND
aka Steward 28B1250-000. They are .875" high, 1.25" OD and .75" ID.

Using piece of wire 3" long bent into a U shape. Measurements are
Magnitude and Angle of the vector.

Freq.
(MHz) Bare Wire Single Bead Two Beads
.5 .58 @ 29.0 4.62 @ 68.2 9.0 @ 70.3
1 .74 @ 46.0 8.09 @ 70.2 15.8 @ 71.0
2 1.15 @ 62.1 14.36 @ 70.2 28.0 @ 70.4
4 2.08 @ 74.7 25.30 @ 67.0 49.6 @ 66.3
8 4.04 @ 81.8 42.00 @ 61.6 81.7 @ 60.3
16 8.01 @ 85.5 68.50 @ 56.4 132.7 @ 54.0
32 15.93 @ 87.3 105.40 @ 46.9 204.0 @ 42.3
64 31.80 @ 88.4 145.10 @ 37.4 279.0 @ 27.9
110 56.30 @ 89.0 181.00 @ 30.6 333.0 @ 13.2


Remeasuring the Balun.
With the new setup, there is not a big difference in the terminated
measurements, but the peak in the open impedance of the primary winding
went from ~7 Mhz up to 11.4 Mhz.


Freq.
(MHz) Open Inductance 200 Ohm Termination
.5 275 @ 74 49.6 @ 9.2
1 491 @ 72 51.1 @ 5.4
2 897 @ 69 51.8 @ 3.8
4 1731 @ 59 52.0 @ 3.4
8 3710 @ 31 52.4 @ 4.4
16 3460 @ -51 52.6 @ 7.2
32 1261 @ -78 51.9 @ 14.4
64 591 @ -84 51.2 @ 35.7
110 291 @ -83 86.8 @ 76.7

Peak 11.4 Mhz 4850 @ -9.0

--Teh

Teh,

After reading you previous response as the your application I have
some real doubts as to the efficiency and power handling capability of
you unit.

I suggest you may find some very useful information at:

http://audiosystemsgroup.com/RFI-Ham.pdf

The section on baluns begins on page 24, however, my power concern is
addressed on page 26.

I think you find that information valuable.

73,
Danny, K6MHE