# Definition of Source Power for RF Transmisison Line Source

So I know this is going to seem like a very simple question, but my book provides no definition. If the power P_in is defined as the power the goes from the source into the load in a transmission line, what is the source power in terms of the generator voltage, generator internal resistance, and any other relevant constants.

I've seen elsewhere the book that $$P = \frac{1}{2} Re\{VI^*\}$$. In the case of a generator with some internal impedance (resistance in the simple case) Z_G and some voltage source V_G what is the power it can deliver $$\frac{V_G^2}{Z_G}$$ or $$\frac{1}{2} \frac{V_G^2}{Z_G}$$ and why?

I'm just not fundamentally understanding all our different power definitions for these problems, and it would be very helpful if someone could provide a concise summary of what I need to know to tell what's going on. Thanks.

• – C. Lange Sep 11 '19 at 4:35
• I don't know the canonical answer to your question, but I wouldn't consider the power consumed by the generator's internal impedance to be "delivered". So my answer would be different from either of your proposed answers. – The Photon Sep 11 '19 at 4:55
• an RF 'transmission line', 50 ohms, is a very different context to a power 'transmission line', 132kV, which do you mean? While the physics meaning of 'power' is well defined, there will be nominal or rated powers that might be defined slightly differently depending on context, 'source power' is one such power in the RF context. – Neil_UK Sep 11 '19 at 5:09