From: "Terrell W. Fritz"
Date: Sat, 03 Mar 2001 14:32:44 -0700
Subject: Re: [TSSP] Reactive part of base input impedance
Hi Marc, With a little torroid on my coil, I sweeped the frequency from 250 - 255kHz. http://hot-streamer.com/temp/Tek00005.gif The yellow is the voltage out of Paul's box, the blue is the current out of the box, and the red is the resistance. The readout is the lowest resitance point (I almost had to read the manual to figure out how to do that trick :-)). You can see all the waveforms as the coil passes through resonance. You can see in the yellow voltage trace that as the coil comes into tune, the lowering coil input resistance is loading the voltage down a bit as the current shoots up. This illustrates how the loading on the input of the coil changes over frequency. I think in your case, this loading may indeed be having a little effect on your meter and the wiring. I find this stuff is pretty darn sensitive. At one point I could see the diference between having my toes curled or uncurled on the HP meter as I was sitting six feet away! Normally, I would think as the coil comes into tune, and the top voltage was highest, that the resistance on the input would fall and increase the load on the signal generator to drop that voltage a bit. This is what is shown in the pic above. However, the meters and wiring may be having an effect too... Cheers, Terry At 09:55 AM 3/3/2001 -0500, you wrote: >terry, all >i also noticed that at the point of highest topv the base v is at it's >highest point. and i'm not sure it matters but i noticed that at the >absolute mid point of were the highest v waveform, before it starts to >fall off on either a slightly higher or lower frequency input, the base >v waveform is in it's truest sine shape. on my scope this base v wave >has a little bump in the peak, to either side of the frequency this wave >shape would lean towards a leading or lagging type peak, saying that it >would raise predominately to the left or right of the peak? i have video >of this effect and it is how i found the very peak or accurate f1 point. >on the point of highest top v and base v i was pondering whether the >voltage was actually going resonant in my meter, but now i know it's >also seen by others. >great work and great new toy. >marc > >"Terrell W. Fritz" wrote: >> >> 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.