Note: This page was updated on 22-JUNE-2023  . . .

including significant changes based on my research over the past 7 years.


THIS is what most people get wrong when building their OCFD antennas.


Traditionally, most people used a 4:1 Ruthroff (voltage) balun in their OCFD antennas.  In the 1990s, the trend migrated to 4:1 Guanella (current) baluns.

Unfortunately, most 4:1 Guanella baluns were wound onto a single Toroid, which does not work at all; it has zero Common Mode Impedance (CMI).

Eventually people began using dual-core 4:1 Guanella baluns, with a dedicated core for each of the two transmission lines of the balun.  This was a significant improvement and almost worked good enough.  However, even the best 4:1 dual-core Guanella balun has insufficient Common Mode Impedance and requires an additional RF Choke to fully suppress all residual Common Mode Current.



Here are some critical guidelines for an OCFD balun:

  1. The correct impedance transformation ratio is 4:1, not 6:1. 
  2. Do not use a voltage balun (by itself) under any circumstances.
  3. Do not use a single-core current balun under any circumstances.
    • Beware of baluns claimed to be "dual-core" 4:1 current baluns.  When the two cores are mounted touching each other and the wires wound around both together as if it were a thick single core, this is effectively still a single core balun; it just has a thicker core. (Example: Balun Designs 4114ocf).
  4. Contrary to popular belief, the best transformer balun to use is a 4:1 Ruthroff (voltage) balun wound on a single #61 ferrite Toroid.  Using #43 ferrite for this purpose, especially when running digi-modes, often leads to SWR-creep (slowly rising SWR level) due to its low Curie temperature.  It must be followed up by a 1:1 Guanella choke-balun.
  5. For a 40m OCFD, use a Hybrid Balun with a 4:1 Ruthroff balun wound onto #61 ferrite and a 1:1 Guanella balun wound on #43 ferrite.
  6. For an 80m OCFD, use a Hybrid Balun with a 4:1 Ruthroff balun wound onto #61 ferrite and a 1:1 Guanella balun wound on #43 ferrite.
  7. For a 160m OCFD, use a Hybrid Balun with a 4:1 Ruthroff balun wound onto #61 ferrite and a 1:1 Guanella balun wound on #31 ferrite.
  • In IMO, for most of us city dwellers, a 160m OCFD is a waste of time because we can't get it high enough to be efficient.  
  • Instead, I prefer an Inverted-L.
  1. Commercial "Hybrid Baluns":
    • I do not know of any commercial source for this type of balun.  You will have to do it yourself (home brew), but this is relatively simple to build.
    • You can read more about the hybrid balun on the EXCELLENT web Page Steve Hunt, G3TXQ (SK) has on Basic Baluns.
      • The Hybrid Balun is described in "F" in that document.
    • Steve shows one version of the hybrid balun with the 4:1 Ruthroff balun on the TX side and the 1:1 Guanella on the ANT side.  
    • I BUILD MY HYBIRD BALUNS THE OPPOSITE WAY.  I place the 1:1 Guanella on the TX side and the 4:1 (Ruthroff) on the ANT side.  
      • I use #43 or #31 in the Guanella (see above) and #61 in the Ruthroff.  IMO this is the better design.
      • I have discussed my design with Steve and he agreed that this method was sound.
      • I have built and tested several 80m OCFD antennas using my design.  IT WORKS GREAT.
      • I have not tried it like Steve shows it.

THE BIGGEST MISTAKE that people make when home-brewing their OCFD is to take the balun requirements lightly.  They are of utmost importance. 

  • If you deviate from the recommendations above, I'm not saying that you will have problems “no matter what”.  It's the other way around.
  • If you have problems with your OCFD (or any commercial OCFD) then the reason is most likely because you deviated from the BALUN recommendations above.


Building your OCFD antenna using the balun tips above is like driving a car with a good working seat belt, air bag, and a good insurance policy.  Although bad things can still happen, you've done everything possible to minimize the risk.


You will find justification for all of this, elsewhere on my web, mostly on the page titled BAD BALUNS but also in the CMC Test and Battle of Baluns pages.


In the section called "BAD BALUNS" I show a list of several world-renowned experts who have written excellent information about balun selection.  ALL have reached the same conclusion on dual-core vs. single core 4:1 Guanella baluns.


FINALLY:  for a detailed understanding of why this is the best method of building OCFD baluns, see Part-1 of my 2-part video presentation on OCFD antennas.  See Part-2 for details on building your own OCFD balun and antenna. 

See: The Hitchiker’s Guide to OCFD





I am in process of creating a section on my web site dealing specifically with RF chokes.

The information is already there, elsewhere and well hidden.

For now, See: 


MAXWELL CHOKE:  This is pictured in "C" and described farther down the page.


GUANELLA CHOKE:  This is pictured in "A" and "D".  A is not very good and I do not recommend it, unless you are on a field trip and it is the only solution available.  "D" is not only better than "A", it is MUCH better than "C" (Maxwell).


The choke I most often used is described as "D2" near the bottom of the page.  I normally use #43 ferrite for 80 thru 10m.  If I am building a choke for 160m, I use #31 ferrite.




Everything I have stated above is based on my own personal field research on real OCFD antennas.  It is not something I read in a book, heard from someone else, or am speculating on*.


*One Caveat:  I have never tested an OCFD higher than 50 ft. in the air.  I read about the height vs. impedance on Buckmaster's web page and in DL1VU's excellent book on Windom- und Stromsummen Antennen.


I continue to research these facinating antennas and I must occasionally modify some of my previous conclusions.  The information shown here was updated on 22-JUNE-2023.


Others have their own opinions.  Many (most?) may differ from what I show here.  

Do your own due dilligance.  

If someone claims something different, ask them how they know that (where they read that, etc.).

Then ask them if they have personally verified the information, built and measured it themselves... and then watch their face turn RED.  :-)






I wish to thank the following people for their technical support in my 4 year research journey of this antenna.  Without the technical help and encouragement of these fine engineers, I would have been helplessly lost:

  • DJ1AT
  • G3UNA
  • GM3SEK (through G3UNA)
  • G3TXQ
  • K6KBE
  • M0RZF

NOTE: these people have NOT individually endorsed the info on this page, they were my mentors in helping me understand what and how to test, as well as how to evaluate the results.


Computer modeling was done for me by DJ1AT and K8BA.


In addition I received lots of support and encouragement from several members of the Windoms and OCFD Antennas group.  There are too many names to mention here.


Finally, thanks to my good friend and sidekick, Sebastian YO5PNS (DD7SN) who assisted me in the field with most of my tests.


Technical Resources:

Throughout my research I made extensive use of technical information (books, technical papers or web site) from the following OM:   G3TXQ, GM3SEK, K9YC, VK1OD, W2FMI, & W8JI.