Quote:
Originally Posted by NN5I
Think about the tuner-feedline-antenna system. There's 100 watts going out (radiated by the antenna) and 100 watts coming in (from the transmitter). That's the same rate of energy-per-second (100 watts = 100 joules per second), so the same amount of energy is going out as coming in.
There's additional energy running back and forth. Where did it come from? When the key was first pressed and the transmitter started pouring 100 watts in, it took a while for the power radiated by the antenna to build up. At first, with 100 watts coming up, the antenna was radiating only 50 watts. Then, after the first bounce-bounce-round-trip, it was radiating 75 watts. As energy bounced back and forth, eventually the antenna reached a full 100 watts radiated. So, at first, the transmitter was pouring in 100 joules per second and the antenna was radiating less than 100 joules per second. The extra energy got stored and is running back and forth. Energy that's traveling is power, and that's how we get 200 watts going up and 100 watts coming down.
When you release the key, that gradual buildup is undone by a gradual slowdown, and the stored energy finally goes to zero.
Simple stuff, no?
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Thank you, Carl. I am learning lots from this thread. You are a gifted teacher.
I especially enjoyed the watts : joules/sec ratio. I knew the power * time = energy relationship. Comfortable using that for a long time to the point of it being intuitive. Hardly (if ever) thought about rearranging it as energy/time = power. I see the math but I had to think about it for a minute to "feel" it (If that makes any sense).
Also I was unaware of the exact relationship of watts (100) to joules/sec (100). That whole "joules thing" I always recognized as energy but never knew "How much" it was. J = W * S. Simple. I should have looked that up decades ago. Hearing that a megaton atom bomb releases ~4.18 x 10^15 joules never meant too much to me. I had no scale in my head to relate to it.
Now I know that it gets as "hot" as 4 Trillion toasters running for a full second.
Toasty, indeed
.
(PS: I also liked: "Energy that's
traveling is
power". I never thought of it like that. Makes sense. I just hadn't looked at it that way.)
Any homework tonight, Teach?