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Ted's comments and questions about balun function, balun reliability, and coiled coaxial cable baluns, the "Badger" balun, are interesting and thought provoking. In my experience, the older KLM baluns were the older "voltage" mode balun style that relied on flux linkages to create the balun transformer action. Mine failed too. The "Badger" balun, constructed from coiled coaxial transmission line, was developed and popularized to address the limitations of the old style "voltage" mode baluns that were popular 30 years ago. George Badger's contributions were: 1) an organized description, for the amateur audience, of the theory and function of the coiled transmission line version of the "current" mode balun style, that is now popular. 2) measure for the first time, for the amateur literature, the common mode impedance of a coiled transmission line balun using the most modern impedance measuring equipment available at that time. 3) described creative ways in which this style of transmission line transformer or current mode style balun can be configured to deliver impedance transformations. The coiled transmission line balun is the circuit equivalent of a low Q parallel tuned resonant circuit. The result of this balun configuration is to create quite a large common mode impedance on the transmission line over a not very broad bandwidth. These style of "current" mode balun is ideal for a single band system because of it's high common mode impedance and low loss characteristics. The down side of this design is the relatively narrow common mode impedance "bandwidth" and the need to accurately construct and TEST the balun for the desired common mode impedance at the frequency of interest. "Close" may not be good enough for some applications. Real world tribanders such as the KT-34, multibanders such as the C-31XR, and the common practice of co-locating multiple antennas, from 80 meters to UHF, on the same tower demands a much better balun solution. In ALL of these installations, ALL the elements of ALL the antennas couple to each other because of the co-location of all the antennas in each of the other antenna's near field, and the far field for that manner. Success for these types of complex antenna systems relies on 1) minimizing spurious resonances with the different antennas, 2) physical and electrical symmetry of the antennas, and 3) feed line isolation to minimize common mode currents. It is my opinion that ALL the antenna feedpoints should be isolated at ALL frequencies by baluns with sufficient common mode impedance to preserve electrical symmetry and minimize common mode currents. I do not think that coiled transmission line baluns, "Badger" baluns, are the best solution to the problem that Ted is wrestling with. A "current" mode broadband balun, such as the Force-12 B-1 balun would fit the requirements the best. This style of broad band balun will isolate ALL the feedpoints at ALL the antennas through out the HF frequencies for the co-located antennas in the antenna system. The choice of balun is not based on wind load, resistance to birds nests, or cost, but rather based on conservative practice to preserve the desired functional characteristics of the antennas. My experience with the Force-12, B-1 baluns is excellent. These baluns are constructed with ferrite beads strung on Teflon coax. These baluns demonstrate a measured broadband common mode impedance of about 800 ohms from below 40 meters to above 10 meters. They are capable of sustained high power operation and are sealed against the weather. I prefer these style baluns to any that I have used in over 45 years of ham experience. I am very interested in others' thoughts on Ted's question and my views in particular. Regards, John Petrich, W7HQJ -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. Force 12 Web site: http://www.qth.com/force12 Submissions: send to Force12Talk@qth.com To unsubscribe: send a blank e-mail to Force12Talk-leave@qth.com Force12Talk Message Archive: http://www.qth.com/force12/list/force12talk For problems with the list, contact n4zr@qth.com |
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