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

David Robbins k1ttt at verizon.net
Tue Dec 12 12:52:41 EST 2017

Why must a balun provide isolation?  how can a coil of coax be considered a balun as there is no isolation of the currents on the inside of the coax provided like there can be with a transformer.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Ward Silver
Sent: Tuesday, December 12, 2017 17:19
To: towertalk at contesting.com
Subject: Re: [TowerTalk] common mode chokes, baluns and multiband, doublets

 >  "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
- 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


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