From: "Terrell W. Fritz"
Date: Fri, 02 Mar 2001 22:30:08 -0700
Subject: Re: [TSSP] Reactive part of base input impedance
Hi All, I got a new scope! A Tek 3012. The old one is sold so don't bother trying to buy it off me... My TC budget will be a little busted this year :-))) I have been thinking about the "big upgrade" for a long time and... ;-) http://hot-streamer.com/temp/P3010015.JPG While playing with my latest toy, a thought occurred to me considering the last post here. Since the voltage and current maximums into a resonator occur at slightly different frequencies, the maximum power point will be somewhere in between. The trace is my small coil scanned from 305 to 315kHz with a P5100 top probe. http://hot-streamer.com/temp/VmImPm.gif The yellow is top voltage, the blue is current in, and the read is the voltage multiplied by current. So perhaps the "true" F1 is better defined as the point were Vin x Iin reaches a maximum or the input Z is least? I just realized I shouldn't have been looking at top voltage in the scope picture... but rather input voltage... Since the two frequencies, in any case, are very close, this is more of a theoretical concern. I wonder if the "true" f1 is (Fv + Fi)/2 or SQRT(Fv^2 + Fi^2)?? But perhaps the top voltage maxima and the input power maxima are exactly the same frequency... Thus, the "true F1 is not so ambiguous... Much to ponder... Cheers, Terry --------------------------------- Hi Paul, Neat! Great to know the measurements worked out so well! I am getting used to doing this, so this was a very straight forward process this time. I looked at the probed coil for the resonant frequencies you mentioned and got: IbaseMax = 311.85kHz VtopMax = 313.02kHz I plugged the 5100 probe into the HP meter so the frequencies can be determined very accurately. However, the HP meter has a bit of an odd input impedance so the probe/measurement "could" be off a bit. However, I think it is pretty close. The signal generator has a resolution of 0.01Hz and the HP meter reads out to 1uVacrms so the accuracy is super high if it works... The scope is reading about 4.5% high on it's little readout and channel two has a high offset. May be time for a calibration... Cheers, Terry
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.