On Wed, 28 Jun 2006, Roger D Johnson wrote:

Straydog wrote:



because that reflected power will end up being dissipated in the
tube/heatsink.

Another "Old Wives Tale"! Tubes are only "matched" to the point where
the desired output is obtained.

All depends on your definition of matched.

Reflected power will see the amp as a
mismatch and will again be reflected back towards the antenna.

I think that is only partly true. Yes, there will be reflectd power going
back out to the antenna, but there was an article in QST back a number of
years ago. Yes, the mismatch also results in higher plate dissipation,
too. I will correct myself about reflected power being disipated in tube,
but the mismatch will increase the plate dissipation. The other issue is
being off plate resonance. I had my SB-230 trip the overtemp relay when I
moved frequency and did not retune the final.

You also need to allow for loss in the transmission line. Not all of what
gets reflected at the mismatches ends up at the other end of the
transmission line. SWR (i.e. reflected power generated at the
antenna/feedline) would not be a problem if the transmission line
were long and lossy.

73, Roger

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