On May 26, 6:20*pm, Roy Lewallen wrote:
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

But Roy, consider that the source resistance remains constant at 10
ohms. Then what load resistance will absorb the most power? The answer
is 10 ohms. Any value of load resistance greater or less than 10 ohms
will result in less power delivered. I don't believe it's fair to
change the source resistance when dealing with the Maximum Power
Transfer Theorem.

In your example with a source resistance of 10 ohms and a load
resistance of 50 ohms the power delivered will be 1.39 watts. But when
the load resistance is 10 ohms with the same source resistance the
power delivered is 2.5 watts. As I said above, if the load resistance
is either greater or less than 10 ohms the power delivered will be
less than 2.5 watts. Thus when the source resistance is constant the
maximum power will be delivered when the load is matched to the
source.

Nes pa?

Walt