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#27
December 13th 07, 03:01 AM
posted to rec.radio.amateur.antenna
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Standing Wave Phase
AI4QJ wrote:
"Cecil Moore" wrote in message . net... wrote: Although we know that the 200 ohm line is longer, there is no indication that the length of the 600 ohm line must or must not change. The phase shift at the impedance discontinuity depends upon the *ratio of Z0High/Z0Low*. The following two examples have the same phase shift at the impedance discontinuity. Z0High Z0Low ---43.4 deg 600 ohm line---+---10 deg 100 ohm line---open ---43.4 deg 300 ohm line---+---10 deg 50 ohm line---open So how long does the 600 ohm line have to be in the following example for the stub to exhibit 1/4WL of electrical length? ---??? deg 600 ohm line---+---10 deg 50 ohm line---open Based on what you say above, Zo high/Zo low = 6 resul;ts in 37 degrees. Then for phase shift, (Zo high/Zo low)*37 deg = 6*D where D = phase shift. If the above ratio is literally true, then in the above example, 12*37deg/6 = 74 degrees and length of the 600 ohm line = 90-74-10 = 6 degrees. However, I would like to find a reference for the math showing the characteristic impedance ratio relationship with phase shift. I am reluctant to accepting formulas without seeing them derived at least once. :-) Looks like you got the Z0 ratio upside down? Actually I get 25.3 degrees for the 600 ohm line. Arctan(Z0Low/Z0High)cot(10)) = 25.3 degrees -- 73, Cecil http://www.w5dxp.com |
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