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W5DXP wrote:
Roy Lewallen wrote: Magid has the most rigorous derivation of power and energy flow on transmission lines I've seen, as well as other extensive transmission line information. One conclusion that pricked my ears was that on a line with a pure standing wave (e.g., a lossless line terminated with an open or short circuit), ". . . power (and therefore, energy) is completely trapped within each [lambda]/4 section of this lossless line, never able to cross the zero-power points and thus constrained forever to rattle to and fro within each quarter-wave section of this line." He's obviously talking about net energy. There is no impedance discontinuity in a continuous piece of transmission line so there is nothing to cause reflections at the zero-power points. Net energy doesn't cross the zero- power points but equal forward energy and reflected energy must cross the zero-power points. That is easy to prove by observing ghosting on a TV set being fed by 1000 feet of ladder-line. If energy is completely trapped within each 1/4WL section, ghosting would be impossible. I forgot to add. At the "zero-power points", either voltage or current is zero. All that means is that all the energy is contained in the opposite field. If the voltage is zero, the H-field is at a maximum. If the current is zero, the E-field is at a maximum. The energy still exists, just in one field or the other. V*I*cos(theta) is NET energy. The power in the forward wave is Vfwd*Ifwd and the power in the reflected wave is Vref*Iref. Those values are constant all up and down the line for a lossless feedline. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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