W2DU's Reflections III is now available from CQ Communication...
Richard Harrison wrote:
Keith Dysart wrote:
"For the most part, "maximum power transfer is just an interesting
ideosyncracy of linear circuit theory."
In the world of 50 and 60 Hz, we don`t want all the power plant can
supply when we flip on a light switch.
The RF world is usually different.
Maximum power transfer only occurs when source and load match
conjugately, and the match proves the load and source impedances are
equals. It is well known and easily shown that a match results in
maximum power transfer.
. . .
It's also easily shown that it doesn't.
Consider a 10 volt voltage source having a 50 ohm source resistance,
feeding a 50 ohm resistive load. Power at the load is 0.5 watt, is it not?
Reduce the source impedance to 10 ohms.
Now what is the power dissipated in the load?
Is it greater or less than it was when the source and load impedances
were matched?
Roy Lewallen, W7EL
|