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How to use a bird wattmeter for testing vswr?
Im confusing myself over the operation of a bird wattmeter.
For example, If a radio has a rated ouput of 20w and you plug in the bird wattmeter to the output, and it shows 15w. You turn the slug around, would you expect a wattmeter reading of 5w being reflected? Would this give a vswr of 4:1 ? Would this indicate a fault between the radio output and the antenna because of incorrect impedance matching. Would the radio try to increase its power output to 20w to compensate therefore burning out the radio? Is there anything else I am missing.
Im sorry if I have answered my own questions correct. Im just learning and want to make sure I have understand this correctly. Thanks 
Sorry, I ment a vswr of 3:1.
No, using forward and reflected power measurements doesn't work quite like that. You need to do some maths.
The formula is
1 + sqrt.(reflected / forward), divided by 1 - sqrt.(reflected /forward).
So using your 15/5 figures,
sqrt 5/15 = 0.577.
1.557 / .443 = VSWR of 3.5:1.
You can further calculate return loss in dB.
Return loss = 10 log (forward/reverse).
Pretty obviously you will get used to how much reflected power to expect in relation to forward, with continued exposure to the meter's use. Zero reflection is ideal so far as the antenna radiating power!
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