Almost all of us know that "BAL-UN" is the acronym for "BALanced-UNbalanced", thus we grasp the role of the device that bears the name of "balun" - allow to connect a generator having an unbalanced output (asymmetrical in respect to a reference), as is a radiofrequency transmitter with a coaxial transmission line, to a blanced load (symmetrical in respect to the reference), as is a dipole antenna or a lot of other kind of antennas, but not a Ground Plane one. The use of a balun let us avoid some drowbacks that would arise if we connected the unbalanced output directly to the balnced input. Actually, a balun is normally bi-directional, i.e. it allows to connect a balnced generator (the same antenna used to receive) with the unbalanced load (the coax connected to the input stage of the receiver), though this function is generally much less promoted in amateur radio litterature.

Well, let's come to the point. I've just built a choke bal-un, or current balun (with 1:1 impedence transformation ratio, i.e. it's just a balun, not an impedence adapter). I just want to share the pictures that document my work, I hope that they might be useful to someone else and, why not, that someone  will send me his comments and suggestions trough the "Contacts" module of this web site. Honestly speaking, there is nothing new in this article, I just one of the several (thousands? Millions?) realization of a HF choke. However, I'm sure that nobody would come to this misknown web site by chance, and that most of you are here because you are looking for instructions and pictures to be used as a starting point to homebrew your balun. So, read my article and also some of the other articles that you'll find around on the internet and in the litterature. I spent a lot of effort in order to make a tutoprial that suits to individuals who  don't have specific technical skills, commenting and showing all the mounting operations, including the trivial ones...

Let's build a wide band choke balun for HF, with a good hope that it'll work on 50 MHz band too. We'll realize it with 10 turns of RG-142 coax cable wound on two overlapped toroids, brand Amidon model FT240-43. Why exactly 10 turns? The choice is based on expreimental data published by G3TXQ (SK), who gave the figures for 9 turns; since 9 turns would bring to a geometrically asymmetrical realization, and also in order to compensate a part of the leakage flux due to the much higher stiffness of the RG-142, when compared to the RG-58 used by G3TXQ, which results in less tight turns around the core, I've decided for 10 turns instead of 9. This balun should withstand a power of few kW, but I would not know how to verify that, I can run only 100Wembarassed.

 Needed material and equipment:Some of the materials needed for the balun homebrewing

  • a piece of RG-142 coax, let's say about 1,3 meters. The price is between 7 and 11 Euros/m in a shop (I paied it 5 Euro/m at a fair)
  • two Amidon toroids FT240-43; price about 9-10 Euros each
  • panel mounting female UHF connector (or, if you prefer, panel mounting N type female connector); price starting from 2 Euros

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This article is not for beginners. Specific electrical/electronics education is required as well as experience in the field of medium and high voltage circuits..

Observe all suitable precautions and safety rules. If you are wondering what they are, it means that this project is not for you!

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