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## [TowerTalk] VSWR & Power

 To: [TowerTalk] VSWR & Power realex@flash.net (realex) Sat Mar 1 22:12:17 2003
 ```If one directly measures the voltage, current and associated phase angle (in radians) for the 3:1 mismatched line shown below (hard to do on a coax but easy on twin line) then, E x I x Cos Theta(rads)= 100 Watts...the applied power. This is true for all points on the line. Example: a 50 ohm line at least 1/2 wavelentgh long at the frequency of interest, terminated in a 3:1 mismatch with 100 watts applied will have E=77.80, I=2.06, and Theta(rad) = -.9 at some point on the line. 77.80 x 2.06 x Cos(-.9) = 100 watts. ((ignoring resistive losses of the line)) 73, Bob, W5AH -----Original Message----- And if you have an open or short circuit, VSWR is infinite, and so are the forward and reverse power! In real life, Tx power goes somewhere - into tuner and transmission line resistance - and VSWR is finite. -Martin Chuck, W1HIS wrote: ... (2) A meter between the tuner and the antenna will indicate Forward power = 133.33 watts; Reverse power = 33.33 watts; % refl. power = 25 %; VSWR = 3:1; and the _net_ forward power is 133.33 - 33.33 = 100 watts. Note that the forward power exceeds the power output from the transmitter because the 33.33 watts of reverse power returning to the tuner is reflected from the tuner back toward the antenna. ```
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