Heyho,
I need a slap onto the back of my head so the bits fall into place. Also, yeah, asking this is kinda embarrassing. I feel stupid. Google doesn't really help here. It all says that my instruments are wrong.
The Oszilloscope (actually five) says Vpp=30V. The Wattmeters says ~8W. I say 'eh?'
If I'm not stupid, then "calculating P on 50R from VPP" works like this:
Vpp / 2 = Vp
Vp / SQRT(2) = Vrms
Vrms˛/R = P
Which is:
30Vpp / 2 = 15Vp
15Vp / SRQT(2) =~ 10,6Vrms
10,6Vrms˛ = 112,3 / 50R = 2,24W
That's theory. But all five power meters say "approx 8W".
The circuit draws ~1A @ 12V. So 8W out divided by 12W in is n= 67%, which sounds resonable. Also, power loss (heat) feels normal. So it checks.
What is it that I'm missing here?
Some small voice in the back of my head says "theory only looks at the positive swing. But the negative also contains energy, which makes it twice" (double the voltage = 4 times the power. Which would check. I could also run this through Fourier, which also requires to ignore the negative swing but uses two times the positive swing).
30Vpp / SRQT(2) =~ 21,3Vrms
10,6Vrms˛ = 453,7 / 50R = 9W
So, gimme a slap please.
Edit: read values from an CB Radio with Po=4W. Powermeter says: ~4W. Oszilloscope says: Vpp = 20V. Checks with my theory. But I'm none wiser.
Greetings,
~Zazzle