The w2au is the preferred balun of amateurs worldwide. The main category is rf chokes that is about radio frequency chokes. A balun or line isolator substantially reduces i 4 current. In all of the following, i will assume that the balun is a 1. Some aspects of the balun problem rf communication. Use a ferrite bar from a am receiver or better, a toroid. This design is engineered by w2fmi to be 98% efficient which means little heat will be created inside the balun during operation.
The most common way balun design mistakes get into public domain is by improper or incomplete testing. It is interesting to know that the original design of the w2du ferrite bead balun is a spinoff from the development of antenna systems designed for spacecraft built. Teflon type coax is used in this current balun surrounded by ferrite doughnuts. This led me to an investigation of just how baluns are supposed to. Newer and inferior designs w2dus design is 50 years old thats old fashioned certainly something newer must be better. A trick to identify the specific wire by making it a bit longer at both ends. Walt was best known in the amateur radio realm for his groundbreaking series of articles, another look at reflections. The internal feed line passes through ferrite beads which prevent rf current from flowing on the coax shield. The maxwell bead balun has a useful peak common mode impedance from 160 through 15 meters. The w2du s rf choke design can be used anywhere along your coaxial transmission path to help eliminate rf feedback and tvi. Windings are inserted into teflon tubes increasing total breakdown to 10,000 volts.
Wireman model 827 balun is the w2du design available with so239 on one end of a pvc enclosure and 6 pigtails on the other end. With modern ferrite materials, and our better understanding of balun characteristics than in varneys day, there is no reason not to include a ferritecored 1. W2au baluns are transformer designs with ferrite cores to provide 95% minimum coupling efficiency. I had to strip the outer cover of the coax off so that the beads would fit over the coax. Like ford vs holden, canon vs nikon or yaesu vs icom. The peak amplitude of the signal is about 5 db below that of the balunfed antenna and one of the nulls, 30 degrees from broad side, is just as deep as was the null off the end of the balunfed antenna.
The w2du balun increases dramatically both the resistance and reactance for the. There are a couple of points about this trace that need to be considered. I am the original designer of the w2du current balun, described in qst, march 1983. Even at high swr levels, the w2du baluns wont generate harmonic radiation. I believe this experiment shows at least to my satisfaction that the parasitic capacitancetoground effects of the 4191a, when measuring devices with a large amount of conductive surface area such as my 12turns of 12 awg wire inductor can greatly skew the impedance measurement, and that the s21 technique is a better way to go. In essence it said, in this breakthrough article, w2dus peerless 1. A nonradiating balanced transmission line requires that the current in. A nonradiating balanced transmission line requires that the current in the two conductors be the same. Basic balance quality test for current baluns a guanella or current baluns functional quality can be evaluated by moving a ground common with signal source to points a, b, and c figure 1 while watching voltages or currents in the load, or. Most of our units are derived from the researched and tested designs of dr. This link is listed in our web site directory since sunday jul 27 2008, and till today a model of the w2du 1. That means that nearly all of the i 2 current is radiated by the antenna, and none by the feed line. A brief report of some of the experimental data that led to the design of the commercial version of the w2du balun are shown in sec 21. While the rf currents flowing along the coax shield are choked out by the balun isolator, the internal 50 ohm signal is completely unaffected.
Turn all the coils at the same time and connect them. The w2du is the preferred balun of amateurs worldwide. Walter maxwell, w2du, died july 3, 2012 at his home in deland, florida of natural causes. The antenna pattern improves and most of the rf current flowing down the outer surface of the coaxs shield is eliminated. Chapter 21a how the w2du ferrite bead balun originated. Following equation or formula is used for rf lc balun calculator. The internal feedline passes through ferrite beads which prevent rf current from flowing on the coax shield. This is actually a ferriteloaded coaxial rf choke which just happens to yield the same result as a 1. How the w2du ferrite bead balun originated it is interesting to know that the original design of the w2du ferrite bead balun is a spinoff from the development of antenna systems designed for spacecraft built by rcas astroelectronic division, specifically the antenna system developed by the author for. I made no attempt to patent the device, and anyone can build it. The balun is a transmission line transformer tlt some baluns are narrowband because they depend on a section of transmission line that is a. Inline baluns provide similar performance to their respective wire balun counterparts. Long the standard of the industry the w2au baluns are built to last. Current baluns are the balun of choice in all but very specialized situations, because they work better than voltage baluns in most realworld systems.
Some aspects of the balun problem by walter maxwell w2du rf. He measured 50, 100, and 200 bead chokes 200 beads best, 4x impedance of 50 beads much better noise suppression, better power handling commercial w2du balun only 50 beads or less w2dus beads are tiny. Wideband balun design with ferrite cores senior project california polytechnic state university, san luis obispo paul biggins june 21, 2014. Jerry sevick and are hand wound with best available components to provide highest possible efficiency. Even at high swr levels, the w2du balun will not generate harmonic radiation. Each has a builtin lightning arrestor, hang up hook, and 600 lbs. To properly match the 50 ohm coaxial cable to the feedpoint impedance the balun performs the 4to1 transformation 50 ohms 4 200 ohms and the opposite for receiving which converts the 200 ohms to 50 ohms. If some of the greek characters dont come through ill have to repost with the material changed from word to pdf as an attachment, so here goes.
The diagram on the right shows what can happen if you dont include the balun. Applications for inline baluns include line isolation anywhere along the coax transmission system and use on quad and yagi antennas. The force 12 balun has a good peak common mode impedance from 40 meters to 10 meters. The balun device is used to balance inherently unbalanced systems by canceling or choking off unbalanced current flow.
Balun designs established in 2005, balun designs builds exceptional quality baluns and ununs for amateur radio, military and commercial applications. A hams guide to rfi, ferrites, baluns, and audio interfacing. The w2dus rf choke design can be used anywhere along your coaxial transmission path to help eliminate rf feedback and tvi. The w2du balun shown in attached photo is a lowpower version using 50 amidon fb732401 cores slipped over a 1foot length of rg58 coax. Join thousands of satisfied visitors who discovered antenna, rf circuit design and rf power. In the professional literature as i noted in a recent cq artcie. It has little or no effect on i 1 and i 2 currents.
The w2du maxibaluns owe their extremely high power capability to the fact that they contain no ferrite cores to saturate. Since then designs have evolved dramatically, and applications have evolved beyond driving differential antennas to include balanced mixers, amplifiers, and signaling lines of all types. The figure depicts typical lc bridge configuration. The wire man also has w2du baluns available both in kit form and fully fabricated, ready for installation. It is a choketype balun that consists of a number of small ferrite cores placed directly over a section of coaxial cable where it is connected to the antenna. It is interesting to know that the original design of the w2du ferrite bead balun is a spinoff from the development of antenna systems designed for spacecraft.
However, some of the companies who manufacture the w2du balun have come up short on the quality of their product, resulting in poor, and sometimes disastrous reports concerning. The design is a variation of an order1 transmission line transformer described. While the rf currents flowing along the coax shield are choked out by the balunisolator, the internal 50 ohm signal is completely unaffected. An inexpensive, highperformance, ugly 50 ohm balun building a nogrief 1. Order quantities of 4 or more units may increase production time. The unadilla w2du hf maxibalun owes its extremely high power capability to the fact that it contains no ferrite cores to saturate. Locate a pill bottle or other nonconductive cylinder or piece of pvc pipe at least 3 in diameter. Dont believe anyone who claims to be an expert on baluns. The balun has a long and illustrious history, first documented in the literature as a device to feed the television transmitting antenna for the empire state building1 in 1939.