I was reading about an Off-Center Fed Dipole (OCFD) antenna.

The following statement was made:

"An effective balun can be made by coiling up coax providing it is
self-resonate at or very near the operation frequency"

In the above statement, what does "self resonate" mean?

Lee KA0FPJ

On Dec 10, 12:55*pm, " wrote:
I was reading about an Off-Center Fed Dipole *(OCFD) *antenna.

The following statement was made:

"An effective balun can be made by coiling up coax providing it is
self-resonate at or very near the operation frequency"

In the above statement, what does "self resonate" mean?

Lee *KA0FPJ

in that context it means that the coil of coax has distributed
capacitance and inductance that at some frequency presents a parallel
resonant circuit which makes a high impedance for currents on the
shield of the coax. you can see the effects in the table on my web
site (http://www.k1ttt.net/technote/airbalun.html) where there are
peaks in the impedance of the air core 'baluns'... it is actually more
correct to call them chokes than baluns since they really just try to
choke off the current on the shield of the coax at the feed point.

On Fri, 10 Dec 2010 05:55:15 -0800 (PST), K1TTT
wrote:

it is actually more
correct to call them chokes than baluns since they really just try to
choke off the current on the shield of the coax at the feed point.

Some balance needs to be returned to this (pun intended). The
expression BalUn is first and foremost found in what this word means
in full: Balance/Unbalanced and THAT is the principle transformation.
Turns ratio may come, but that is variable (2:1, 4:1, 6:1...) to a
design that must first meet the requirement of isolating one side that
is balanced from the other side that is unbalanced.

This is achieved in choking common mode currents - hence the BalUn
must effectively present choking action to meet this principle
transformation.

73's
Richard Clark, KB7QHC

On Dec 10, 4:49*pm, Richard Clark wrote:
On Fri, 10 Dec 2010 05:55:15 -0800 (PST), K1TTT
wrote:

it is actually more
correct to call them chokes than baluns since they really just try to
choke off the current on the shield of the coax at the feed point.

Some balance needs to be returned to this (pun intended). *The
expression BalUn is first and foremost found in what this word means
in full: Balance/Unbalanced and THAT is the principle transformation.
Turns ratio may come, but that is variable (2:1, 4:1, 6:1...) to a
design that must first meet the requirement of isolating one side that
is balanced from the other side that is unbalanced.

This is achieved in choking common mode currents - hence the BalUn
must effectively present choking action to meet this principle
transformation.

73's
Richard Clark, KB7QHC

here comes the troll statement...

currents are always balanced and there is no transformation. the
currents in a coax are already balanced, on the inside. the action of
the choke is to prevent current from flowing on the outside of the
shield back to the inside at the antenna feed point. this forces the
return path to be the other half of the antenna if all works
properly.

let the balun wars commence!

On Fri, 10 Dec 2010 04:55:21 -0800 (PST), "
wrote:


I was reading about an Off-Center Fed Dipole (OCFD) antenna.

The following statement was made:

"An effective balun can be made by coiling up coax providing it is
self-resonate at or very near the operation frequency"

In the above statement, what does "self resonate" mean?

Lee KA0FPJ


It means take the coax feeding your OCF dipole and, at the end where
it attaches to the OCF balun, wind it into a coil about 6 inches in
diameter, 8 turns, tape it together so it doesn't uncoil and run the
rest of the coax to the rig.


Check out this diagram -- the guy calls his a "choke balun" -- 6 turns
of coax, 100 mm diamter turns.
http://www.vk3eg.org/technical/xlwindom/xlwindomhtm.htm


This balun is designed for use with and OCF dipole -- it has a
built-in 1:1 balun -- no need for a coax balun (coax choe) as it's
built into the balun.
http://www.balundesigns.com/servlet/...4-cln-1/Detail


Here's one guy's decription of how he built an OCF dipole using the
above balun:
http://w4hh.org/station%20antennas.htm


This guy uses 6-7 turns of coax, 6 inch diameter, as a coax
balun/choke.
http://hamradionation.com/document.p...for-40m-to-10m