Poor Jon is going to think I'm picking on him but I must disagree on his
statements about
conjugate matching of amplifiers. In reality the PA tube is only matched
to the extent that
it produces the desired power output. We can see this by the design
steps required. First,
the output power is selected. Then we pick a tube and a reasonable anode
voltage to
produce that power. Then we compute the necessary current and multiply
that by a fudge
factor for the class of operation. The anode voltage is divided by the
previous value and
that gives the impedance the tube must work into to produce the desired
power output. A
matching network is then designed to transform that impedance to 50 ohms
(usually).
Notice that at no time was the actual output impedance or load
resistance of the tube used!
The fact that the tube is not "matched" to the load also explains why
most of the reflected
power is again reflected at the amplifier and goes back towards the
antenna.
73, Roger
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