[TowerTalk] common mode chokes, baluns and multiband doublets

Wes Stewart wes_n7ws at triconet.org
Tue Dec 12 13:21:28 EST 2017

Jim has seemingly made the study of the construction, measurement and 
application of "common-mode chokes" his life's work.  His heroic efforts are to 
be applauded. Nevertheless, he and I see some things, from politics to 
baluns...oops...differently and we often get (respectfully) sideways with each 
other.  (I've often thought that Jim believes that there isn't anything in life 
that can't be improved by the judicious application of a common-mode choke:-) )

Here is one of those times where we disagree.  I said earlier "we find it to be 
a perfectly fine term, widely understood and accepted in professional literature."

Proof of this can be seen in a few references from my files:


and so on and so forth. The fact that many different devices can, and are, used 
to perform an unbalanced-to-balanced transformation does not make the term a bad 
one any more than using a term like transistor. What if using "transistor" 
required a description worthy of a semiconductor physicist? The same applies to 
transformer, choke, diode, inductor, capacitor, etc.  We use these terms on a 
daily basis with little, if any, concern.  I really fail to understand the 
heartburn too many hams have over the use of this word.

Wes  N7WS

  On 12/11/2017 10:24 PM, Jim Brown wrote:
> YES, YES, YES!  Let's use the correct word to describe things. FAR less 
> confusion.
> Several points in this discussion.
> Kevin Stover, Wes Stewart, and David Gilbert are entirely correct in their 
> posts.  2-wire line by itself does NOT make a system balanced. Current on the 
> two conductors will be equal and opposite ONLY if the rest of the system is 
> balanced. But many (most?) wire antennas that we hams CAN rig are unbalanced 
> by their surroundings -- ground slope, unequal heights of the two ends, 
> surrounding conductors (in buildings, trees, other antennas, towers that 
> support them). They are also BADLY unbalanced if the two lengths are unequal 
> (like OCF "dipoles").
> Dean Straw, N6BV, retired editor of the ARRL Handbook and Antenna Book, wrote 
> an excellent applications note that ran in QST about 2 years ago (April '14 or 
> '15?) in which he observed that badly matched antennas place very high voltage 
> and current points along the antenna, and either can fry even the most robust 
> of common mode chokes.
> The first solid work I've seen published on 2-wire common mode chokes was by 
> W2FMI. He reported that the Zo of closely spaced #12 enameled wire is about 50 
> ohms, and is in the range of 90 - 100 ohms for #12 THHN. When I first started 
> winding those chokes I confirmed his observations, and I've recently measured 
> some #12 teflon pairs with Zo in the range of 105 - 110 ohms. These values 
> will, of course, depend on details of the dielectric material and it's 
> thickness. We're using #12 THHN chokes on #31 cores to choke high wire dipoles 
> (feedpoint Z in the range of 75-88 ohms, depending on height and the soil 
> under them) and #12 enameled copper to feed 50 ohm Yagis.  The design of the 
> Force 12 C3SS that we use for portable operation does NOT like the THHN 
> chokes, but works very well with the enameled wire chokes.
> I've done a lot of work studying this, and published it both on my website and 
> in the ARRL Handbook. k9yc.com/publish.htm   On the basis of that work, I do 
> not believe that it is practical to effectively choke any badly matched 
> antenna at any power level above 100W, and even at 100W it's easy to fry a choke.
> While Wes is a superb engineer, I strongly disagree with him about use of the 
> word "balun"  -- I can think of nearly a dozen very different parts or 
> products that are called "balun."  Indeed, the great confusion about what they 
> are and how they work (or don't work) is CAUSED by using the same word to 
> describe very different things.
> 73, Jim K9YC
> On 12/11/2017 8:29 PM, EZ Rhino wrote:
>> Why don’t we permanently retire the term “balun” and use either “choke” or 
>> "impedance transformer” in its place?

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