(ANTENNA) BALUNs
Few Topics are as Confusing and Misunderstood as the BALUN.
FACT #1: A BALUN is a Transmission Line Accessory, NOT an Antenna Accessory.
FACT #2: BALUNs are described in the Transmission Line Chapter of every ARRL HANDBOOK, NOT in . the Antenna Chapter!
. When mentioned in the Antenna chapter, it says "see the TRANSMISSION LINE chapter)".
FACT #3: THE MAIN PURPOSE of a BALUN is to prevent Common Mode Current from flowing on the . Transmission Line, thus maintaining a balance in Differential Current (i.e., equal current but . opposite polarity) flowing in each of the two lines of the transmission line.
FACT #4: TRANSFORMER BALUNS are baluns with a secondary function of transforming the impedance . to some ratio other than 1:1 (i.e., 4:1, 9:1, etc.). If the device does not impede the flow of . Common Mode Current, it is just a transformer, not a BALUN.
FACT #5: This probably contradicts what you may have heard or thought to know about BALUNs.
Rather than try to convince you in my own words, I will provide LINKs to experts on this topic and let you choose what you wish to believe after reading them.
The very first thing we must agree before going further is what the task of a BALUN is and how it accomplishes it. This was best described in a paper by Roy Lewallen (W7EL) - the author of EZNEC Antenna Modelling Software - and published in Volume One of The ARRL ANTENNA COMPENDIUM.
In that paper, Roy coined the terms "Current BALUN" and "Voltage BALUN". Prior to that they were known as Guanella BALUN and Ruthroff BALUN.
- If you have never read this paper, I STRONGLY SUGGEST you read it now.
- If you have already read this paper, I suggest you re-read it before continuing.
LINK: Baluns: What They Do And How They Do It
NOTE: Roy gives a presentation on BALUNs every year at the Dayton Hamfest.
CAUTION: THE WEB IS A DANGEROUS PLACE TO STUDY BALUNs
It has been said that Elvis is still alive and living together with JFK on a dark alley in New Orleans, building voltage baluns in their basement. (hi) READER BEWARE!
MY ADVICE: Study BALUN technology only from the experts:
- DG0SA Wolfgang Wipperman (SK)
- G3TXQ Steve Hunt (SK)
- GM3SEK Ian White
- K9YC Jim Brown
- VK1OD Owen Duffy
- W1HIS Chuck Counselman
- W2DU Walt Maxwell
- W7EL Roy Lewallen
- W8JI Tom Rauch
I'm sure there are several other reliable sources, but I don't know them all.
These listed above are the ones I know or know of and can recommend.
Perhaps you are wondering why W2FMI / Jerry Sevick is missing from the list above.
It is with good reason.
Sevick has written an excellent book (which I recommend reading) entitled Understanding, Building, and Using Baluns and Ununs (published by CQ Communications Inc., ISBN: 0-943016-24-X).
In this book, Sevick shows us how to build just about every type of balun we hams might typically want to use. Unfortunately, he has made a few mistakes in the book, and left out some important topics. These will be documented on a separate page: Sevick's Book
IMO he leaves the reader with the false impression that the way he is showing to build these devices is the 'only' way to build them. He neglects to mention that different applications (i.e., different types of antennas, different frequencies, etc.) may need more or fewer turns of transmission line, and in some cases even a different ferrite mix.