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## [TowerTalk] loss resistance

 To: [TowerTalk] loss resistance W8JI@contesting.com (Tom Rauch) Mon, 15 Oct 2001 10:15:41 -0400
 ```> >Think about that Pete. If the loss resistance were in parallel > >with the feed impedance, then the higher the LOSS resistance, > >the LESS it's effect would be. NOT logical. > > > >The Loss resistance is in SERIES. > > Tom's right, of course, but .... if I measure R=7 at the bottom of my > shunt feed, and the tower is only grounded by three ground rods and 4 > x 125 foot radials, how much of that series combination is loss, and > how much is the feedpoint? It's hard for me to imagine that the loss > component is only 7 ohms. It may not be 7 ohms Pete. It is a mistake to simply assume the deviation you see from a certain feed impedance directly translates to loss. In order to sort loss resistance from radiation resistance you have to measure the resistance at one point in the system, then enclose the entire system in a very large conductive enclosure and measure the change in resistance. While that is sometimes done at UHF, it is a big task at lower frequencies and impossible on 160. The ONLY way the FCC accepts data on loss is by measuring field strength along a long path distance in several directions. You measure the slope of attenuation to estimate the ground conductivity (poorer ground has greater attenuation with distance), and then use that slope to predict what the FS should be for a perfect radiator over the same ground. Everything is normalized to that value by factoring in estimated losses by the slope of attenuation. While far from ideal, the FCC method is the best thing we have for low frequencies. Base impedance is unreliable because of all the other things around our antenna, and because some ground losses do NOT show as an increase in base resistance. 73, Tom W8JI W8JI@contesting.com List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems, Trylon Titan towers, coax, hardline and more. Also check out our self supporting towers up to 100 feet for under \$1500!! http://www.anwireless.com ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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