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## [TowerTalk] 75 ohm feedline

 To: [TowerTalk] 75 ohm feedline k1ttt@berkshire.net (David Robbins) Wed, 09 Jul 1997 00:25:52 +0000
 ```L. B. Cebik wrote: > > scenario: cut your line with precision to keep the equipment adjustments > flat and minimal or use transformers with attention to proper wx treatment > for your area and climate for the same purpose, with comparable > losses--which are negligible in either case relative to all the other loss > sources that might enter such systems. No wonder folks have claimed > success for both ways of doing things. just another thing to throw a monkey wrench in the works... do some rough calculations: compare wavelengths at the two busiest frequencies on 80m in contests 300/3.5mhz = 85.7m 300/3.8mhz = 78.9m difference = 6.8m shorten by velocity factor 6.8*.66(?)=4.5m so the wavelength changes by 4.5m in the hardline (even assuming the smallest velocity factor i know off hand) from 3.5 to 3.8 mhz. this ammounts to about an 8% or an almost 30 degree change for a one wavelength line. go to 2 wavelengths and the shift is almost 60 degrees. so cutting to a half wavelength multiple is not so easy, unless you are restricted to a narrow bandwidth. similar effects can be calculated for other bands, just remember that the same physical length 'contains' more wavelengths as you go up in frequency. i use random lengths of 75 ohm hardline (cut to fit and never measured) with no matching transformers. i do have a couple pieces of rg-11 that i use to balance out some bands inside the shack where its easy to play around with them. and the losses i have with 50 ohm loads plus home made plumbing fitting connectors is so low i could not measure it for sure with amateur grade meters at hf. i could see a measureable loss on 2m, but no more than i could attribute to the predicted losses from the cable itself. -- David Robbins K1TTT (ex KY1H) k1ttt@berkshire.net or robbins@berkshire.net http://www.berkshire.net/~robbins/k1ttt.html -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
 Current Thread [TowerTalk] 75 ohm feedline, Bob Locher [TowerTalk] 75 ohm feedline, Pete Smith [TowerTalk] 75 ohm feedline, Greg Clark [TowerTalk] 75 ohm feedline, L. B. Cebik [TowerTalk] 75 ohm feedline, David Robbins <= [TowerTalk] 75 ohm feedline, Bill Fisher, W4AN