I'm looking for input regarding the common mode (choking) impedance
for 4:1 current baluns. A friend recently purchase a commercial 4:1
current balun and, out of curiosity I set it up and measured the
common mode impedance and was very surprised at the performance I saw.
A very narrow range peaked at about 1.58 MHz. (The unit's rated
frequency range is 1-30 MHz.)

I have no experience with this type of balun having always used 1:1
ratios and I'm wondering if this is typical for this type of balun.

Because one doesn't post binary attachments on this news group I have
placed a schematic and a common mode impedance plot for the balun
along with a reference plot for a commercial 1:1 balun at;
http://k6mhe.com/balun.html

73,
Danny, K6MHE

Danny Richardson wrote:
A very narrow range peaked at about 1.58 MHz. (The unit's rated
frequency range is 1-30 MHz.)

I once bought a commercial 4:1 balun wrapped on a
type 2 powdered iron core rated for "all-HF" operation.
The performance sucked. I had the factory measure the
choking impedance and it did indeed suck. Sorry, I don't
remember the exact results but it was designed by Jerry
Sevick, W2FMI, and described on page 34 of "Building
and Using Baluns and Ununs".
--
73, Cecil http://www.w5dxp.com

Because of the folding back of the currents I would not expect the 4:1
step up transformer to be a stirling performer at common mode
rejection...
The best way to approach this is to use the 4:1 transformer balun
strictly as a transformer, then add a 1:1 choke balun in series with
it...
Personally I would wind the coax into a solenoidal choke balun
immediately below the 4:1 transformer being thrifty and all that and
call it good...




denny / k8do

How are you connecting it to measure the common mode impedance? I don't
think you can just connect the input leads together and output leads
together like you do with a 1:1, but I haven't taken the time to think
much about how you really should measure it. . .

Roy Lewallen, W7EL

Danny Richardson wrote:
I'm looking for input regarding the common mode (choking) impedance
for 4:1 current baluns. A friend recently purchase a commercial 4:1
current balun and, out of curiosity I set it up and measured the
common mode impedance and was very surprised at the performance I saw.
A very narrow range peaked at about 1.58 MHz. (The unit's rated
frequency range is 1-30 MHz.)

I have no experience with this type of balun having always used 1:1
ratios and I'm wondering if this is typical for this type of balun.

Because one doesn't post binary attachments on this news group I have
placed a schematic and a common mode impedance plot for the balun
along with a reference plot for a commercial 1:1 balun at;
http://k6mhe.com/balun.html

73,
Danny, K6MHE

On Mon, 13 Nov 2006 14:25:52 -0800, Roy Lewallen
wrote:

How are you connecting it to measure the common mode impedance? I don't
think you can just connect the input leads together and output leads
together like you do with a 1:1, but I haven't taken the time to think
much about how you really should measure it. . .

Roy Lewallen, W7EL

Yes, I measured with the leads connected together as you described.
However, after I posted my question this morning I looked around and
found I had an Elecraft BL-1 current balun. This balun can be
connected as a 1:1 or 4:1 by just moving two wires on the circuit
board - no other changes are necessary.

I measured the BL-1 in both configurations, using identical methods
which show close agreement.

You can see the results at: http://k6mhe.com/elecraft.html

Danny, K6MHE

Hm, I'll have to think about that one a bit. I checked out the Elecraft
info and it appears that the balun is wound on a single binocular core,
not two separate cores. You could make a 4:1 current balun that way if
you could manage to keep the flux from one pair of windings from
coupling to the other, but I don't know right off how you'd do it. I
suspect that some sort of complex winding scheme might make it work. But
if the one you're trying to measure really has two separate cores, I
suspect that measuring the Elecraft might not be a good test of the method.

Roy Lewallen, W7EL

Danny Richardson wrote:

Yes, I measured with the leads connected together as you described.
However, after I posted my question this morning I looked around and
found I had an Elecraft BL-1 current balun. This balun can be
connected as a 1:1 or 4:1 by just moving two wires on the circuit
board - no other changes are necessary.

I measured the BL-1 in both configurations, using identical methods
which show close agreement.

You can see the results at: http://k6mhe.com/elecraft.html

Danny, K6MHE

On Thu, 16 Nov 2006 05:24:14 -0800, Roy Lewallen
wrote:

Hm, I'll have to think about that one a bit. I checked out the Elecraft
info and it appears that the balun is wound on a single binocular core,
not two separate cores. You could make a 4:1 current balun that way if
you could manage to keep the flux from one pair of windings from
coupling to the other, but I don't know right off how you'd do it. I
suspect that some sort of complex winding scheme might make it work. But
if the one you're trying to measure really has two separate cores, I
suspect that measuring the Elecraft might not be a good test of the method.

Roy Lewallen, W7EL

Don't know. However, the folks at Elecraft have a good reputation for
excellent designs so I banked on that.

Going back the original balun I used (which uses separate cores), you
where concerned about tying the leads together for measurements. I,
for the sake of me, can't see why this would be wrong. After all, we
are talking common mode impedance here and the unit did show excellent
choking impedance at its resonate frequency (about 1.58MHz.). But had
a very narrow range. (dropping from over 6K @ 1.58 MHz. to less than
1K @ 3.5 MHz., 700-ohms @ 7 MHz, less than 300-ohms @ 14 MHZ and the
lowest was 130-ohms @ 30 MHz.

To me, that seemed to be lousy performance for a balun advertized
range of 1-30 MHZ.

Danny, K6MHE

Danny Richardson wrote:
After all, we
are talking common mode impedance here and the unit did show excellent
choking impedance at its resonate frequency (about 1.58MHz.). But had
a very narrow range. (dropping from over 6K @ 1.58 MHz. to less than
1K @ 3.5 MHz., 700-ohms @ 7 MHz, less than 300-ohms @ 14 MHZ and the
lowest was 130-ohms @ 30 MHz.

Did you also measure the phase angle for those readings?
--
73, Cecil, http://www.qsl.net/w5dxp

On Thu, 16 Nov 2006 14:55:02 GMT, Cecil Moore
wrote:

Did you also measure the phase angle for those readings?

Yes, at resonance it was, of course, 0º. From 3 to 30 MHz. it varied
between -61º to -81º.

Danny

Danny Richardson wrote:
Cecil Moore wrote:
Did you also measure the phase angle for those readings?

Yes, at resonance it was, of course, 0º. From 3 to 30 MHz. it varied
between -61º to -81º.

Is the inductive side of resonance of no use in
that type of balun?
--
73, Cecil, http://www.qsl.net/w5dxp