[TowerTalk] common mode chokes, baluns and multiband, doublets

[Ward Silver]

 >  "Balun", def: the most misused and misunderstood word in all of ham 
radio.

My approach, when discussing baluns, is to present the "balun" as a 
"function," not necessarily a "thing."

The balun "function" is to transfer power between balanced and 
unbalanced systems while at the same time providing isolation between them.

Any "thing" that implements the function can be considered a "balun."  
There are lots of "things" that implement the "function."

For example, here's a list of "things" that are all considered to be 
"baluns":
- coil of coax
- coax wound on ferrite cores
- coax through ferrite beads
- quarter-wave sleeve
- Guanella transmission-line structure (a.k.a. "current balun")
- Ruthroff transmission-line structure (a.k.a. "voltage balun")
- half-wave transmission-line structure
- etc

Some of the "things" also implement impedance transformation, but 
impedance transformers don't necessarily perform the balun "function," 
adding to the general confusion.

73, Ward N0AX