Steve Hunt wrote:
Jim,
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 :)
73,
Steve G3TXQ
Jim WA9YSD wrote:
Found this nice table. Thought I would pass it along.
http://www.firestik.com/Tech_Docs/SWRLOSS.htm
Keep The Faith, Jim K9TF/WA9YSD
Steve,
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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