I picked up a 1:1 balum at a local hamfest, i got it because it had a
N connector and thats the type of connector on my coax. After looking
closer i thought it was a 10-40 meter but i
cant make out the print, it may be 10-40mhz.
I desided to open the pvc to find out just what was inside, I found a
bunch of ferrite disk stacked over the coax, this wasent my idea of a
1:1 balum. I hoped to make a 160-10 meter
dipole/inverted vee using the proper length wire on each leg for
160,80,40 & 10. My question
is this, will this work at lower frequencys 160 & 80m ? If not what the
purpose of the ferrite
disks, it seems that i could just remove the disk if they limit the
frequency range, i guess
im trying to inderstand what makes this a balum & what purpose the disk
serve?

You'll find the answer at http://w2du.com/r2ch21.pdf.

Roy Lewallen, W7EL

wrote:
I picked up a 1:1 balum at a local hamfest, i got it because it had a
N connector and thats the type of connector on my coax. After looking
closer i thought it was a 10-40 meter but i
cant make out the print, it may be 10-40mhz.
I desided to open the pvc to find out just what was inside, I found a
bunch of ferrite disk stacked over the coax, this wasent my idea of a
1:1 balum. I hoped to make a 160-10 meter
dipole/inverted vee using the proper length wire on each leg for
160,80,40 & 10. My question
is this, will this work at lower frequencys 160 & 80m ? If not what the
purpose of the ferrite
disks, it seems that i could just remove the disk if they limit the
frequency range, i guess
im trying to inderstand what makes this a balum & what purpose the disk
serve?

wrote:
I desided to open the pvc to find out just what was inside, I found a
bunch of ferrite disk stacked over the coax, this wasent my idea of a
1:1 balum.

You have what is commonly known as a W2DU 1:1 balun-choke
made popular by Walter Maxwell. It's probably not very
effective on 80m and 160m because of the choice of
ferrite materials.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
wrote:

I desided to open the pvc to find out just what was inside, I found a
bunch of ferrite disk stacked over the coax, this wasent my idea of a
1:1 balum.


You have what is commonly known as a W2DU 1:1 balun-choke
made popular by Walter Maxwell. It's probably not very
effective on 80m and 160m because of the choice of
ferrite materials.

If you can get an ohm reading when you touch the two probes of an ohm
meter to the ferrite, then it is probably a low frequency, high
permeability manganese zinc ferrite, and may produce enough common
mode impedance to act effectively as a 1:1 balun in this frequency
range.

If you measure an open circuit, it is almost certainly higher
frequency, lower permeability nickel zinc ferrite and will produce
insufficient common mode impedance to be effective as a balun in this
frequency range.

It is used to reduce the common mode current which sometimes flows in
coaxial and balanced-pair lines.

It is not a transformer. The 1-to-1 is meaningless. It is just a pair
of wires wound together, as one wire, on a ferrite core. Or in your
case a number of ferrite slugs or rings are placed over a coax line.

In brief, it is just a choke.
----
Reg.

Reg Edwards wrote:
It is used to reduce the common mode current which sometimes flows in
coaxial and balanced-pair lines.

It is not a transformer. The 1-to-1 is meaningless. It is just a pair
of wires wound together, as one wire, on a ferrite core. Or in your
case a number of ferrite slugs or rings are placed over a coax line.

In brief, it is just a choke.

But a choke with two wires wound through it is two inductors that also
have mutual inductance between them, and if that doesn't define a
transformer, what does?

It is true that this device acts as a choke for common mode current
(the component of the two currents through the two conductors that is
in phase). A choke is an inductance, which produces voltage across
the terminals of the conductor passing through that is proportional to
the rate of change of the current. In this case, it produces a
voltage across both the shield section inside the cores and also
across the center conductor inside the cores, that is proportional to
the rate of change of the common mode current. It is this voltage
that alters the displacement currents in the two terminals at the
antenna end, to make them look like a more balanced signal, and at the
transmission line end, more like a single ended one.

On Tue, 28 Mar 2006 12:05:01 -0500, John Popelish
wrote:

But a choke with two wires wound through it is two inductors that also
have mutual inductance between them, and if that doesn't define a
transformer, what does?

Hi John,

Then you think of it as an air core transformer with series driven,
bucking sections. Now, what kind of practical transformer does that
define? 1:1 does not automatically spring to mind unless it is
isolating one circuit from the other. However, it is not the
transformer that does that, it is the choking ferrite and only in the
service of snubbing common mode currents.

With this in mind, do we add a characteristic of loss to the
definition? A lossy air core transformer with series driven, bucking
sections.

You are bordering on stretching the definition of power transformer
over the application of a BalUn. This is not always useful. So, what
does it transform? A balanced circuit to an unbalanced circuit (or
versa vice).

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Tue, 28 Mar 2006 12:05:01 -0500, John Popelish
wrote:


But a choke with two wires wound through it is two inductors that also
have mutual inductance between them, and if that doesn't define a
transformer, what does?


Hi John,

Then you think of it as an air core transformer with series driven,
bucking sections. Now, what kind of practical transformer does that
define? 1:1 does not automatically spring to mind unless it is
isolating one circuit from the other. However, it is not the
transformer that does that, it is the choking ferrite and only in the
service of snubbing common mode currents.

With this in mind, do we add a characteristic of loss to the
definition? A lossy air core transformer with series driven, bucking
sections.

Air core? It is a ferrite core transformer with two one turn
windings. One winding is the shield passing through the holes in the
cores and the other winding is the center conductor passing through
the windings. (view with fixed width font, like Courier)

|half of dipole
. |
Center cond.-----MMMM-+

I mainly wanted to know if it would work on 160 & 80m, I dont care
if it acts like a choke/balun only at higher frequencys as long as
as it doesnt interfere with 160 & 80s swr. Normally i just use coax
hooked to each leg cut to frequency, without a balun. Its allways
worked in the past years, i just thought it would be alot easier to use
the ready made balun than try and makeup a weatherproof
hanger

On Tue, 28 Mar 2006 12:59:52 -0500, John Popelish
wrote:
With this in mind, do we add a characteristic of loss to the
definition? A lossy air core transformer with series driven, bucking
sections.

Air core? It is a ferrite core transformer with two one turn

Hi John,

If there's a transformer in the sense of windings; then it is an air
core, the ferrite is wholly transparent to the transverse currents.
You could remove the ferrite and it wouldn't make a bit of difference
in that sense of transforming.

this current mismatch would cause the transformer to
produce more or less voltage across the windings
In fact, nothing of that sort happens - at least not by your
description. The ferrite is simply bulk resistance inserted into the
common mode path. That is why common mode current is suppressed. The
same thing occurs in the coiled transmission line choke, but the
resistance is replaced by reactance. Again, common mode current is
snubbed by encountering this too.

The transformer property is in the isolation of the balanced circuit
from the unbalanced circuit through this resistive characteristic.

You are missing one path. The two from the source in the form of the
inner shield of the coax, and the center conductor, and the one from
the load in the form of the outer shield of the coax (same shield, but
isolated circuits). Further, there is no flux linkage of the two
conductors coming from the source. Their magnetic lines never break
the cores, whereas the common mode current does break the core which
thus inserts the resistance of the ferrite.

73's
Richard Clark, KB7QHC