24-08-2012, 09:57 AM
Yes, but as I said in post #17, that's where you're going wrong.
In post #7, you don't explicitly say it, but the strong implication (backed up by the above post) is that you're doing a standard impedance test; adjust R until reading has halved, then Rin = R. But that only works for voltage, not power. You need to measure the voltage at the input of the power meter. An AVO will probably do, but use an RMS sensing DVM if you have one.
I've now explained this twice in hand-waving terms, and Al has made two posts explaining it in mathematical terms, including proof that your 5 ohms is in the right ballpark for Zin = 8 ohms. Job done
Cheers,
Mark
In post #7, you don't explicitly say it, but the strong implication (backed up by the above post) is that you're doing a standard impedance test; adjust R until reading has halved, then Rin = R. But that only works for voltage, not power. You need to measure the voltage at the input of the power meter. An AVO will probably do, but use an RMS sensing DVM if you have one.
I've now explained this twice in hand-waving terms, and Al has made two posts explaining it in mathematical terms, including proof that your 5 ohms is in the right ballpark for Zin = 8 ohms. Job done
Cheers,
Mark
