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## [TowerTalk] Grounding unused feed lines -

 To: towertalk@contesting.com, larryj@teleport.com [TowerTalk] Grounding unused feed lines - CubexCo@aol.com Mon, 13 Mar 2006 17:49:16 EST
 ```In a message dated 3/13/2006 4:02:02 PM Eastern Standard Time, towertalk-request@contesting.com writes: From: "larryjspammenot@teleport.com" Subject: Re: [TowerTalk] remote antenna switch To: towertalk@contesting.com What are the cases for a remote coax switch with unused antennas being Grounded, or UNgrounded? For example, I have a 5-band quad with an RCS-8V remote coax switch. So there are four unused bands on the quad with one active, since I have five separate feedlines. ================================= Larry, In general it is best to have the unused quad loops appear "OPEN" to minimize some of the potential interaction. Regards "static" or EMP dissipation as long as you are feeding direct with coaxial cable the shield will always provide a DC path. Now the problem is achieving the "OPEN" condition because it is a complex relationship between the length of the feed lines, VF and the frequency of the band in use. Each unused feed line will have a different "electrical" length depending on those three variables, Cable Length, VF and TX frequency. As you know a "quarterwave" cable terminated in a SHORT reflects an OPEN at the other end. On the other hand a HALF WAVE cable length would reflect a SHORT at the other end. Given the harmonic relationship of some bands the feed line could look like a Half wave, or some fraction which will transform some different complex Z to the antenna termination. The answer is not easy to find - first try it (shorting jumper), observe the results, compared to being open. Antenna patterns (forward lobe shape and F/B) can be effected by the different cases). If there is an obvious "bad" effect, then change the length of the feed line to that loop. There is some analytical work being done on just what are the optimum individual feed line lengths would be to minimize interaction. First drafts have been completed, but it still needs some refinement before it can be published. Regards, Norman W4QN "The Power of a Cubex Quad" http://www.cubex.com/ _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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