From: "Terrell W. Fritz"
Date: Sun, 18 Feb 2001 17:03:55 -0700
Subject: Re: [TSSP] Reactive part of base input impedance
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 At 09:53 PM 2/18/2001 +0000, you wrote: >Terry wrote: > >> For the bare small-coil no top-probe I get: >> >> Q = 170.03 >> >> f1 = 358.81 >> V = 0.47218 (corrected scope) >> I = 2.6234 mA >> >> f45low = 357.87 >> V = 0.48419 (corrected scope) >> I = 1.9908 mA >> >> f45high = 359.89 >> V = 0.48419 (corrected scope) >> I = 1.8823 mA > >First, we can extract from these a measurement of Lee, since > > Rin = w Lee/Q, > >we have, at f1, Rin = 0.47218/2.6234e-3 = 180 ohms, so > > Lee = Q Rin/w = 13.58 mH > >and the predicted value is 13.66 mH, +0.6%. No problem there. > >Now to check the slope of the reactance. Near f1, > > Zin(w) = Rin + jwLin( 1 - (w'/w)^2) > >so at +45 degrees phase, > Rin = 2 pi f Lin ( 1 - (f'/f)^2) >or > Lin = Rin/2/pi/f/(1-(f'/f)^2) >therefore, using f45high, > Rin = 0.48419/1.8823e-3/sqrt(2) = 181.89 ohms > Lin = 181.89/2/pi/359890/599e-5 = 13.42 mH > >At -45 degrees phase, > Rin = - 2 pi f Lin ( 1 - (f'/f)^2) >so > Lin = Rin/2/pi/f/((f'/f)^2 - 1) >and using f45low, > Rin = 0.48419/1.9908e-3/sqrt(2) = 171.98 ohms > Lin = 171.98/2/pi/357870/526e-5 = 14.53 mH > >The average of these two is 13.98 mH, +2.3% from the predicted Lee, >and -15% from the predicted Les of 16.41 mH. So the result is rather >nearer Lee than Les. That's a good result. > >The small coil and new coupling box are doing quite well there Terry, >you've measured and verified Les and Lee in quick succession to quite >a decent accuracy. I don't suppose anyone in the coiling community has >done these before. Hopefully a few more measurements along these lines >will become available - it will all help to establish the validity of >these equivalent reactances and demonstrate that they are real and >measureable. I'll be preparing a web page summarising your Zft, Les, >and Lee measurements, so let me know if you put up any related pages >at your end. Althogether, this is a great step forward, as pn2511 is >distinctly lacking in references to these kind of results. > >I expect you'll be glad to know that I'm scheming up a way to measure >Cee also. > >The 45 degree phase readings are going to be most useful, as I try to >figure out just what's going on with the base impedance, and why the >Qi always seems to be a little higher than Qv. Note the lopsided >variation of Rin, I'll be taking a closer look at this to make sure >the model reproduces the same values. > >Incidentally, the 'new formula' predicts an f1 of 356.7 kHz, -0.6%, >for this coil. > >BTW, next time you're playing with the probed small coil, have a look >and see if you can see the difference between the frequency of >max Ibase and the frequency of max Vtop - it is likely to be very >small, with max Ibase lower in frequency than max Vtop. > >Cheers. >-- >Paul Nicholson, >Manchester, UK. >--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.