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## Re: [TenTec] SWR VS Power Loss

 To: geraldj@storm.weather.net, Discussion of Ten-Tec Equipment Re: [TenTec] SWR VS Power Loss Michael Tope Discussion of Ten-Tec Equipment Fri, 04 Jul 2008 15:37:31 -0700 mailto:tentec@contesting.com>
 ``` 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 _______________________________________________ TenTec mailing list TenTec@contesting.com http://lists.contesting.com/mailman/listinfo/tentec ```
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