Peter Chadwick wrote:
>So there's an optimum output load impedance
>(resistance is a particular case of impedance) which is where the device
>can provide the volts and amps.
ARRL has done quite a good job of purging the term "output impedance"
from the PA chapters of the Handbook, in favor of talking about the
"optimum load impedance" that the PA wants to look into.
However, you still design the output network AS IF the device had an
output impedance that is the conjugate of that optimum load impedance.
Even though that design assumption is usually untrue, it does give us
the correct output network.
In other words, the thing that we carelessly call "output impedance" for
design purposes is purely FICTIONAL. I think that's why Tom calls it
"non-dissipative" - because it doesn't actually exist.
The true (and therefore dissipative) output impedance of the device is
usually much lower than the optimum load impedance, which is what allows
efficiencies greater than 50%.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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