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 :)
>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 losseless 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..............................................
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