Dr. Gerald N. Johnson wrote:
oes not compute! 1 KW forward and 1/2 KW reflected says 1.5/.5 = 3:1
SWR, not 6:1. E.G. SWR = (forward + reflected) / (forward - reflected).
6:1 SWR is 71.45% reflected, 1.7145/0.2855..
What that table means is rubbish.
73, Jerry, K0CQ
Hey Jerry,
VSWR = (1 + |RHOv|)/(1-|RHOv|)
For VSWR = 6:1, |RHOv| = 0.71 (i.e. 1.71:/0.29)
Return Loss = 20*log(|RHOv|) = 20*log(0.71) = -3dB
I think you forgot to square the voltage reflection coefficient when
calculating return loss (easy mistake to make). Ergo, I think the table
values are numerically is correct, but the table is probably easily
misapplied given the supporting material and the context. As Ken N6KB
points out, the table is only very useful if you have an isolator at the
transmitter output (or perhaps a big resistive attenuator pad).
Happy 4th!
73, Mike W4EF........................
P.S. Here is a good "cheatsheet" for checking calculations:
http://www.microwaves101.com/encyclopedia/calvswr.cfm
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