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#1
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Jack Painter wrote:
Walt & Roy, thank you both very much for your lifetime of service to radio. Have either of you analyzed any the numerous popular Radio Works "Current Baluns"? No, since I figured out what baluns do and wrote the article, I've never purchased a balun since I know how to make effective ones myself. When I wrote the article, the popular commercial baluns were all "voltage baluns", and I'd like to think that the article was a factor in causing the gradual changeover of commercial products to "current baluns". I was advised many years ago that the current-type balun was more effective for use with a dipole, and have used Radio Work's baluns on both dipole and random wires with success. But my measure of success is not analytical, as your studies have been. Operating a center-fed dipole at it's resonant frequency, slightly below that, and significantly above it, are the specific inquiries wrt current baluns - would a voltage balun be more effective in any of those conditions? Your question indicates that my article failed to explain one of its major points. The answer is no, a voltage balun is not more effective than a current balun in any antenna/feedline application. If the antenna is perfectly balanced, the third winding in the voltage balun will carry no current and does nothing. If the antenna isn't balanced, the presence of the voltage balun's third winding will prevent balanced currents in the elements. So at best the voltage balun does as well as a current balun, and otherwise it degrades balance. Radio Works current baluns the same kind used in your studies? Sorry, I've never purchased one and taken it apart. You might try asking them. Thanks for your comments, and the great participation of all in this group. You're welcome. I'm surprised and frankly disappointed that so many people haven't seen the article before. It's been in print for 20 years, and frequently mentioned on this newsgroup and elsewhere. There are a lot of other good articles in the _Antenna Compendium_ series -- people who don't have a set have been missing a lot. But it seems like, more and more, that the web has become the sole source of information for a growing number of people. Make that the web, AM talk radio, and Fox news. Roy Lewallen, W7EL |
#2
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On Sat, 19 Mar 2005 14:38:32 -0500, "Jack Painter"
wrote: "Walter Maxwell" wrote Yes, Roy's article in the Compendium is excellent, as are all of Roy's contributions to our art. In his article he referenced my work with baluns, which appeared in QST for March 1983. This article is also available on my web page at www.w2du.com for those who don't have a copy of that issue of QST. Walt Maxwell, W2DU Walt & Roy, thank you both very much for your lifetime of service to radio. Have either of you analyzed any the numerous popular Radio Works "Current Baluns"? I was advised many years ago that the current-type balun was more effective for use with a dipole, and have used Radio Work's baluns on both dipole and random wires with success. But my measure of success is not analytical, as your studies have been. Operating a center-fed dipole at it's resonant frequency, slightly below that, and significantly above it, are the specific inquiries wrt current baluns - would a voltage balun be more effective in any of those conditions? Radio Works current baluns the same kind used in your studies? Thanks for your comments, and the great participation of all in this group. Jack Painter Virginia Beach, Virginia Thanks, Jack, for the nice words--they're appreciated. Walt |
#3
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Roy and Walter,
CHOKE BALUNS. Keep it simple. Why make a song and dance about it? The pair of wires wound on a choke balun behave as an inductive choke for longitudinal currents and as a transmission line for balanced currents. The two circuits, line and choke, behave independently of each other. The actual current on a wire, if anyone should ever wish to know, is just the arithmetical sum of the other two. All authors omit to say that the the pair of transmission line wires need not be coaxial. They can be a balanced twin line such as a length of stranded flexible speaker cable. Or just a pair of insulated wires laid alongside each other. Or twisted. Not only is the twin-line mechanically more convenient to construct, it has electrical advantages. Its Zo is intermediate between the high and low terminating impedances. Typically Zo is about 120 -130 ohms. The geometric mean of 50 and 300 ohms is 122 ohms. Not that this matters very much because the device is never terminated in its nominal impedances. Twin line also has a higher velocity factor than 50-ohm coax. The length of line wound on the choke behaves as an impedance transformer. So it seriously, but not harmfully, affects the impedance presented to the tuner. The tuner LC settings may be beneficially affected. Otherwise the transformation ratio, which heavily depends on frequency, is not of consquence. Preferably, the length of twin-line wound on the choke should be less than 1/8th of a wavelength long at its own velocity at the highest operating frequency. It is not too difficult to construct a choke balun which has sufficient inductive choking reactance at 1.8 MHz without the transmission line exceeding 1/8 wavelengths at 30 MHz. ---- Reg, G4FGQ |
#4
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A few further comments.
For perfectionists, the attenuation along a twin-line wound on a choke balun, is appreciably less than a coaxial line of about the same length. This is due to the lower Zo of the coax and also due to the very small inner coaxial conductor diameter and its higher loss resistance. This is not of great conseqence. The length of line involved is quite small anyway. Less than 1/8th wavelengths at the highest frequency of interest. The power-handling and voltage-handling ability of twin-line is also greater than coax line. So, in general, a choke balun wound with Radio Shack, 18 SWG speaker cable, is cheap, easier to construct, works better, and is more power efficient than the small-bore coax usually used. ---- Reg, G4FGQ |
#5
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Walt, I intended to include a link to your article and looked on your
web site for it before I posted my article. But I didn't find it in the index. Where is it relative to your home page? I'll add a link to it. Walt's article was really the first one I ever saw that explained the phenomenon of currents on the inside and outside of the coax -- my article is really just an extension of his work. Roy Lewallen, W7EL Walter Maxwell wrote: Yes, Roy's article in the Compendium is excellent, as are all of Roy's contributions to our art. In his article he referenced my work with baluns, which appeared in QST for March 1983. This article is also available on my web page at www.w2du.com for those who don't have a copy of that issue of QST. Walt Maxwell, W2DU |
#6
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![]() "Roy Lewallen" wrote Walt's article was really the first one I ever saw that explained the phenomenon of currents on the inside and outside of the coax -- my article is really just an extension of his work. Roy Lewallen, W7EL Roy, Although no credit is given or author claimed, the Radio Works Product Manual includes a similar drawing and detailed explanation of same. This has been in print every year for at least the 6 years that I have been buying products from them. It is the basis for their design, production and marketing of the current-type baluns. Radio Works also recommends a line isolator at the transmitter-end, due to near field coupling of antenna currents onto the coax shield that a Balun cannot prevent. I have never used that product but it is popular. Jack |
#7
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On Sat, 19 Mar 2005 12:35:48 -0800, Roy Lewallen
wrote: Walt, I intended to include a link to your article and looked on your web site for it before I posted my article. But I didn't find it in the index. Where is it relative to your home page? I'll add a link to it. Walt's article was really the first one I ever saw that explained the phenomenon of currents on the inside and outside of the coax -- my article is really just an extension of his work. Roy Lewallen, W7EL Walter Maxwell wrote: Yes, Roy's article in the Compendium is excellent, as are all of Roy's contributions to our art. In his article he referenced my work with baluns, which appeared in QST for March 1983. This article is also available on my web page at www.w2du.com for those who don't have a copy of that issue of QST. Walt Maxwell, W2DU Roy, I changed the address to my web page on 3-13-05 to the one listed above. I also changed the format somewhat.for better organization. The new page lists the pertinent categories with links to the individual chapters from Reflections and its appendices. You'll find the chapter on baluns under the category "Read Chapters from Reflections 2," with the title, "Some Aspects of the Balun Problem," Chapter 21 in the book. Thanks for the assist. Walt, W2DU |
#8
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On Sun, 20 Mar 2005 03:21:56 GMT, Walter Maxwell wrote:
On Sat, 19 Mar 2005 12:35:48 -0800, Roy Lewallen wrote: Walt, I intended to include a link to your article and looked on your web site for it before I posted my article. But I didn't find it in the index. Where is it relative to your home page? I'll add a link to it. Walt's article was really the first one I ever saw that explained the phenomenon of currents on the inside and outside of the coax -- my article is really just an extension of his work. Roy Lewallen, W7EL Walter Maxwell wrote: Yes, Roy's article in the Compendium is excellent, as are all of Roy's contributions to our art. In his article he referenced my work with baluns, which appeared in QST for March 1983. This article is also available on my web page at www.w2du.com for those who don't have a copy of that issue of QST. Walt Maxwell, W2DU Roy, I changed the address to my web page on 3-13-05 to the one listed above. I also changed the format somewhat.for better organization. The new page lists the pertinent categories with links to the individual chapters from Reflections and its appendices. You'll find the chapter on baluns under the category "Read Chapters from Reflections 2," with the title, "Some Aspects of the Balun Problem," Chapter 21 in the book. Thanks for the assist. Walt, W2DU I forgor to mention that I recently wrote an addition to Chapter 21, Chapter 21A for Reflections 3, telling what led to the development of the W2DU balun. It also appears on my web page under the category "Preview Chapters from Reflections 3," The idea came while fixing a problem that arose in measuring the radiation patterns of antennas I developed for use on various spacecraft at the antenna lab of the RCA Space Center, Princeton, NJ in the 1970s Walt, W2DU. |
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