OCFD BALUN SELECTION

 

"Balun Selection" is 'the' most critical success factor of the OCFD.

 

Here are some critical guidelines:

  1. Unless your OCFD will be at least 25m high (80 ft.), use a 4:1 balun not 6:1.
  2. Do not use a voltage balun (by itself) under any circumstances.
  3. Do not use a single-core current balun (by itself) 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 still a single core balun - just has a thicker core.
      • The Balun Designs Model 4114ocf is a good example of this.  On its own it is inadequate.  You may still use it, provided you use it in conjunction with a good 1:1 Guanella choke.  Info on RF chokes is at the bottom of this page.
  4. For a 40m OCFD, use a dual-core 4:1 current balun (Guanella balun) with #43 ferrite mix. 
    • Most (perhaps all) 4:1 current baluns on the commercial market use #61 or at best #52 ferrite mix. THESE ARE NOT USUALLY GOOD ENOUGH.  They have insufficient CMI for the task.
      • In case you still want to use one of these baluns, you MUST also use a good RF choke in addition to  the balun.  Normally a Maxwell choke should suffice, but if your antenna is not hanging free and clear, it will probably have more common mode current (CMC), so use a Guanella choke.
      • The Balun Designs Model 4115ocf is probably the best balun of this type that is commercially available, but it does not use #43 ferrite.  Therefore I strongly suggest using a Maxwell choke with this balun for 40m OCFD antennas.
  5. 80m is dangerously critical.  No standard balun alone is adequate for the job.  You MUST use a combination of 4:1 balun and 1:1 Guanella choke.
    1. If you use large #43 ferrite mix in the two cores, and your antenna is hanging free and clear of obsticles, then a simple (but good) 1:1 Maxwell choke will suffice.
    2. If you use #43 and your antenna is not hung in the clear, you will need more CMI to cope with the CMC.  In that case, use a good 1:1 Guanella choke.
    3. ALTERNATIVE:  use a "Hybrid Balun".   This is a combination of 4:1 transformer and 1:1 Guanella choke.
      • 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 has on Basic Baluns.
        • The Hybrid Balun is described in "F" on that page.
  • IMPORTANT NOTES:  
    • 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 in the Guanella and #61 in the Ruthroff.  IMO this is the better design, but IT IS ONLY MY OPINION - I DON'T KNOW.
      • I have discussed my design with Steve and he agrees that it is OK to do it this way.
      • I have built and tested several 80m OCFD antennas using my design.  IT WORKS GREAT.
      • I have not tried it like Steve shows it.

   6.  160m is similar to 80m, except you should use #31 core material in the choke part of the balun.  

  1. 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.  
  2. Instead, I prefer an Inverted-L.

 

NOTE:  Numbers 2 and 3 may be combined with a 1:1 GUANELLA choke to create a hybrid balun, as referred to in number 5.3.

 

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 recomendations 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 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.

 

BTW, one page shows a link to my own research work.  

I did not mean to imply that I am an expert - I'm not.  I'm just the messenger.

All of the other gentlemen I point out in that section are the REAL experts.

 

---------------------------------------------------------------------------------------------------

 

RF CHOKES:

 

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:  http://www.dj0ip.de/vertical-antennas/rf-cmc-choke/ 

 

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.

 

FOR THE RECORD:

 

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 Exception:  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 written on 26 November 2015.

 

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.  :-)

 

FEEDBACK  WELCOME:  CONTACT

 

Acknowledgement:

 

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 hopefully 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 Yahoo!Group on Windoms and OCFD Antennas.  There are too many names to mention here.

 

Finally, thanks to my good friend and sidekick, Sebastian YO5PNS (DO5PNS) 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, W2FMI, & W8JI.

 

-------

DJ0IP