BAD BALUNS
(Or "how to build a great balun that DOES NOT WORK.)
There are many different kinds of baluns:
- Voltage Baluns, Current Baluns, 1:1 Baluns, 4:1 Baluns, etc.
In general, baluns are a very simple device and very easy to build (home brew), but for some reason most people are afraid to build their own baluns.
WORSE YET, most people seem to believe that all baluns were created eqally and will work equally well, no matter what. THIS IS FAR FROM TRUE!
Your balun will only work well for you if you choose the right technology and build it properly. Unfortunately there is a lot of bogus information on the Internet about which technology to use and how to build it.
CAUTION: THE 4:1 GUANELLA BALUN IS USUALLY SHOWN W R O N G !
It is commonly accepted that a 4:1 Guanella balun may be built by winding two 1:1 Guanella baluns (current balluns) onto a single toroid core and wiring them together is a specific way. Unfortunately if you do it this way, it will not work. In fact it is not even a balun - at least not when used with hf antennas!
THE COMMON PROBLEM WITH MOST 4:1 GUANELLA BALUNS
Most 4:1 Guanella baluns, as well as most of the instructions showing how to build a 4:1 Guanella balun use just one single toroid as the core for winding the two transmission lines onto.
This concept will not work.
If you build it like this or buy one like this, you will not have a balun at all.
In order for a 4:1 Guanella balun to function properly, each of the two transmission lines MUST be wound on its own separate toroid core. This mandates using two cores. For higher power you would use 4 cores (two pairs of two cores glued together).
REVIEW: WHAT BALUNS DO AND HOW THEY DO IT (by W7EL*)
According to Roy Lewallen, W7EL, the main thing a balun should do is "cause the currents in the feed-line conductors to be equal in magnitude and opposite in phase, resulting in a zero imbalance current."
Notice that the balun's job is to keep the feedline balanced,
NOT THE ANTENNA!
*W7EL is the author of EZNEC antenna modeling software. In 1985 his paper entitled "Baluns: What They Do And How They Do It" was published in the ARRL's "Antenna Compendium Volume 1". Roy also gives a presentation on baluns every year at Dayton, explaining to his audience what baluns do.
Download PDF: Baluns: What They Do And How They Do It
Once we agree on the true task of a balun when used in typical antenna applications,
it is easy to understand what is wrong with the single core 4:1 Guanella balun.
FACT IS: A 4:1 Guanella balun wound as two 1:1 chokes onto a common core will force voltage and current IMBALANCE with any non-floating load. AND, all typical antennas are non-floating loads.
Since a balun's job is to maintain balance
and this device forces an imbalance,
it is NOT a balun.
In order for this type of balun to work,
it must be wound onto two cores
with each transmission line on its own dedicated core!
SUPPORTING ARGUMENTS
- VK1OD: 4:1 current baluns - identifying bad ones
- Read his comments on: Sevick’s single core 4:1 current balun
- W8JI: Explanation why single core
does not work.
- (See: "Single-Core Dual Transmission Line Balun" on that page.)
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