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Standing morphing to travelling waves. was r.r.a.a WARNING!!!
Owen Duffy wrote:
"AI4QJ" wrote: not so nicely linear. The antenna is a lossy transmission line just as Owen's example was a lossy xmission line example with a 25 ohm load at No, my example stipulated an ideal transmission line, and by that I mean it to be lossless amongst other things. What we are saying is that even if the transmission line is lossless, the *system* is lossy because of the 25 ohm resistor. If there were no losses in the *system*, the waves on the lossless transmission line would be pure standing waves. Because of the losses in the load, the waves on the lossless transmission line are not pure standing waves, but a mixture of standing waves and traveling waves. In your case (#1 below) the system is primarily a traveling wave system, closer to flat than to an OC or SC stub because only 11% of the forward energy is rejected by the load. You and Cecil are transforming the example to suit yourselves. I'm not transforming the example. You are the one who put the lossy resistor in the system. The traveling waves are the direct result of the installation of the resistor. Let's look at a few different examples and assume the measured joules/sec flowing forward toward the load is 100 joules/sec in each case. 1. Your example of 50 ohm lossless coax connected to a 25 ohm load. The forward joules/sec is 100. The reflected joules/sec is 11.11. The joules/sec consumed by the 25 ohm load is 88.89. 89% of the forward wave is traveling wave. 11.11% of the forward wave is used by the standing wave. The system is primarily a traveling wave system. The energy not delivered to the load is stored in the standing wave in the LCLCLCLC components of the transmission line. 2. No load on the lossless coax. The forward joules/sec and the reflected joules/sec are equal. 100% of the energy is standing wave energy and all of it is stored in the LCLCLCLC components of the transmission line. It does not move from LC to LC. It simply oscillates in place between L and C. EZNEC confirms that the current phasor does NOT rotate. 3. 50 ohm load on the lossless coax. The reflected joules/sec equals zero and the system is flat. 100% of the energy is traveling wave energy. The only energy in the transmission line is the energy it took to fill the pipeline, the delay between power-on and the load dissipating power. The LCLCLCLC in this case is an energy bucket brigade. 4. 500 ohm load on the lossless coax. Of the forward 100 joules/sec, only 33 joules/sec is accepted by the load. The other 67 joules/sec are rejected by the load and become half of the energy in the standing wave. The system is primarily a standing wave system. The energy not delivered to the load is stored in the standing wave in the LCLCLCLC components of the transmission line. -- 73, Cecil http://www.w5dxp.com |
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