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Jim Kelley wrote:
Or maybe it was just too hard for you. It was impossible for anyone to solve without having a math model for the sources. How about a simpler problem then: This is not simpler - it is contradictory. It provides a constant power source with nowhere for the source power to go during steady-state. If you change the source to a Thevenin equivalent then it can be solved. XMTR--X--one second long lossless feedline---infinite ohms PS=100W Please explain how the XMTR can supply 100W during steady- state? Where does the 100 joules/sec go? As stated, this problem, like your other one, is impossible to resolve. If you change the source to a Thevenin equivalent 141.42V and 50 ohm source impedance and specify Z=50 ohms feedline impedance then the problem becomes solvable. The answer is that 200 joules exist in the feedline and, contrary to what W7EL states, will dissipate in the source resistance after the source voltage goes to zero. Note the source resistance is the only resistance in the entire circuit. -- 73, Cecil http://www.qsl.net/w5dxp |
#2
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Cecil Moore wrote:
If you change the source to a Thevenin equivalent 141.42V and 50 ohm source impedance and specify Z=50 ohms feedline impedance then the problem becomes solvable. Going with this configuration which is similar to the 1/2 WL stub suggested by W7EL in his Food For Thought #1: SW Source nc c Pfor=100W-- --Pref=100W 141.4V---o---o---one second long lossless 50 ohm stub--open 50 ohm o---/\/\/\/\/\--Gnd no 50 ohms For the first two seconds after power up, the Thevenin source delivers 200 joules into the stub while dissipating 200 joules as heat in the source resistance. Those 200 joules of energy in the stub must be conserved. During steady-state, assuming the stub is an exact integral number of wavelengths, the source will see an open circuit and be delivering zero power. A wattmeter calibrated for 50 ohms will read 100 watts forward power and 100 watts reflected power during steady-state. After steady-state is reached, we throw the switch and connect the stub to a 50 ohm dummy load. 100 watts will be supplied to the dummy load for two seconds for a total of 200 joules. Who was it who said that reflected power cannot be recovered? (Food For Thought #1 on www.eznec.com). -- 73, Cecil http://www.qsl.net/w5dxp |
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