Jan Panteltje wrote:
Also normally, there is a pi type filter (to prevent harmonics), between
amplifier and antenna.
This filter _WILL_ match the antenna to the output impedance of the
transmitter, so _even_ if the transmitter output impedance is very
very low (low voltage high current output stage for example), the reflected
power will be nicely converted to match the transmitter, and heat up the
output amp, with its possible destruction as result.

Some gurus will say that it's the voltage and/or current
that is destroying the final, not the reflected energy.
They have yet to explain how those dangerous voltages
and/or currents can exist without assistance from the
ExH joules/second in the reflected energy wave. Depending
upon phase, the E in the ExH reflected wave is what causes
the overvoltage due to SWR. The H in the ExH reflected
wave is what causes the overcurrent due to SWR.

The impedance seen by the source is

Z = (Vfor+Vref)/(Ifor+Iref)

Where '+' indicates phasor (vector) addition.

The above equation also gives the impedance anywhere
along the transmission line and anywhere along a
standing-wave antenna.
--
73, Cecil http://www.w5dxp.com