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[TowerTalk] Series Section Transmission Line Matching

 To: TowerTalk [TowerTalk] Series Section Transmission Line Matching David Gilbert Sat, 20 Oct 2007 12:55:24 -0700
 ```I have a question for the math and/or transmission line experts on this list. The ARRL Handbook has some good info on using two different sections of transmission line, each with different characteristic impedances, to match an arbitrary load impedance to the main coax run. The discussion and formulas are on page 16-5 of my old 1990 handbook. I've run a few examples through the formulas and then checked the result with EZNEC and everything seems cool. The Handbook points out that the common quarter wave matching transformer is just a special case of the series section analysis. A quarter wave matching section has the very valuable and much-utilized feature that it converts a voltage forcing function to a current forcing function (with a 90 degree phase shift) so that you can connect two or more feedlines in parallel and force equal currents in their respective loads irrespective of load impedance. So I got to wondering whether a generic series section matching section, even though the lengths of the two sections don't add to a quarter wavelength, might also provide the same current forcing characteristics as a quarter wave one does. I fantasized there might be some phase transformation due to the disparate feedline impedances of the matching sections that would compensate for the actual length. However, as best I can tell after checking currents and phases with EZNEC, that it not the case. The phase shift under a matched condition doesn't typically work out to be 90 degrees, and the actual phase remains simply a function of section lengths and velocity factors. Did I get that correct? 73, Dave AB7E p.s. I loaded the formulas into a very simple EXCEL spreadsheet if anyone is interested ... _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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