On Fri, 2008-07-04 at 11:01 -0700, Michael Tope wrote:
> Steve Hunt wrote:
> >That table could be very misleading without a lot more info.
> >For example, is it showing the total loss, or the "excess SWR loss"?
> >What type of cable is it for? And what length? At what frequency?
> >If you believe the text, it's how the SWR "affects the power output of
> >your radio" ! Pretty good radio that's still putting out 33% of its
> >power into a 10:1 SWR load :)
> >Steve G3TXQ
> >Jim WA9YSD wrote:
> >>Found this nice table. Thought I would pass it along.
> >> Keep The Faith, Jim K9TF/WA9YSD
> This table just shows the percentage of incident power reflected and
> transmitted at a mis-matched RF transmission interface. You'll notice
> that the "% of Loss" versus transmitted power (what they call "ERP")
> always add to 100%. This has nothing to do with "excess SWR loss" on a
> mis-matched lossy cable. As you point out, it also doesn't include the
> impact of power-reduction due to final amplifier bias foldback in the
> presence of a high VSWR. The best way to think of this table is a
> measure of how much power in a short RF pulse would be reflected versus
> how much would be transmitted when that short RF pulse encounters a
> mis-match junction along a very long lossless transmission line. For
> instance, at 6.0:1 VSWR and a short RF pulse say 1KW in amplitude (old
> NTSC TV horizontal sync pulse for instance) hits a damaged antenna on
> transmission line that exhibits a 6.0:1 VSWR at the transmission
> line/antenna interface. According to the chart, 50% of the incident
> pulse power (i.e. 500 watts) would get reflected back toward the TV
> transmitter and 50% would be transmitted into the damaged antenna (i.e.
> the remaining 500 watts). Not terribly useful for most ham applications.
> 73, Mike W4EF..............................................
Does 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
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