Battle of Baluns

A real life comparison test of different balun technologies for use with 80m OCFD Antennas

            All Photos:  DJ0IP

Why Battle of Baluns?


In 2013, I conducted a Field Test of Common Mode Current (CMC) found in 40m OCFD antennas. I began by thoroughly testing simple center fed dipoles, then measured several different OCFD antennas and compared the results with those of simple dipoles.  The test was very complex and led to a few, what I believe to be "new" findings. 


As a result of this test, I determined that the best balun for use with an OCFD is the Dual-Core 4:1 Guanella with #43 ferrite.


In 2015 I built an 80m version of the OCFD antenna using the same balun technology as used in the 40m OCFD designed after my 2013 tests - albeit with a few more windings on each toroid.


To my surprise (and displeasure) the balun was totally insufficient for use on 80m.  But why?


My suspicion was insufficient Common Mode Impedance (CMI) in the balun, which 500 field measurements later, proved to be true. 


To test this, I added first a Maxwell choke to the balun and re-measured, then I replaced the Maxwell with a Guanella choke and remeasured.  The Maxwell almost worked.  The Guanella did work.  But this required 3 cores, not just 2.


I hoped I could find a solution requiring just 2 cores and was determined to try.  However to be sure it would be sufficient, I wanted to try several different combinations and establish a definition of what a good balun solution must be able to do.


To achieve all of this, I defined this Battle of Baluns test.

Mel, K6KBE (one of the 3 co-founders of KLM Antennas in California) helped me to define what and how to test.


The OCFD antenna is known for its problems with Common Mode Current (CMC).  Different configurations and different installation locations can result in different amounts of CMC problems.

For that reason it is very important to have the best possible balun in your OCFD antenna.


From my appraisal of the current (2015) OCFD commercial offering, it is my opinion that the commercial manufacturers of OCFD antennas ("OCFD OEMs") do not understand this antenna and its CMC characteristics.  Their baluns fail (miserably) in having enough common mode impedance (CMI) to suppress the enormous amount of CMC on the feedline of these antennas.


Further more, the commercial Balun OEMs do not understand it either.  All are offering single core 4:1 Guanella baluns which do not work at all, and a few of them are offering dual-core 4:1 Guanella baluns which are much better, yet still insuficient for the chalenges of these OCFD antennas.  


The reason is twofold:

  1. They are using the wrong type of toroid.  Their toroids have too little permeability to get the job done.
  2. They are using too few turns of transmission line on the cores.

In order to put some meat behind my conclusion, I conducted this comprehensive field test on an 80m OCFD antenna and compared the various baluns with each other.


The tests and components tested are described on the next three pages.