From: "Terrell W. Fritz"
Date: Tue, 29 Aug 2000 19:54:54 -0600
Subject: Re: [TSSP] Q mesurements
Hi Paul, OK, I redid the Q measurements with a <0.5 ohm signal generator and measured peak voltage instead of RMS. So I "think" I did it right this time ;-) I put the signal generator and a tiny antenna near to the base of the coil out of necessity but they should not have had any great effect. These are still for the familiar Big LTR coil. 45 inch Torroid coil: Fl2 = 97.28 kHz Fo = 97.84 kHz Fh2 = 98.45 kHz Q = 83.62 Bare coil: Fl2 = 147.1 kHz Fo = 148.4 kHz Fh2 = 149.7 kHz Q = 57.08 I then took my trusty knife and slashed my foil ground plane right down the center with only the center connecting both halves... 45 inch Torroid coil: Fl2 = 96.55 kHz Fo = 97.2 kHz Fh2 = 97.92 kHz Q = 70.95 Bare coil: Fl2 = 145.5 kHz Fo = 147.1 kHz Fh2 = 148.5 kHz Q = 49.03 I remeasured the secondary's inductance at 75.1mH. Looks like the measurements are going a little opposite to what is predicted. I assume that just makes it more interesting and fun :-)) Cheers, Terry At 09:56 PM 8/29/00 +0100, you wrote: >Terrell W. Fritz wrote: >> I will look at this again... > >OK. I like to set the scope gain so the envelope spans >7 vertical divs at resonance, level shifted to +/- 3.5 divs. >Then I detune until its +/- 2.5 divs. > >I found a problem in the calculation of skin depth, was using >a handbook formula, checked and it gave the wrong depths. >Fixed now and the calculated input impedances and Q factors are >revised, > >For Terry's big LTR coil: > > ZMeasured ZModel QMeas QModel >f1 408 ohms 140 ohms 36 148 With toroid. >f1 784 ohms 117 ohms 39 221 Without toroid. > >Which makes a lot more sense, despite the apparent >differences! >I've got a reasonable confidence now in both Terry's >measurements and the computer model. The above measurements >and predictions would all be commensurate with one another if >there was a major additional source of loss in the >resonator, one thats big enough to dominate the total loss. > >I'm thinking of the ground plane, wonder if the coil is >producing massive circulating currents. If so, introducing >some radial slits ought to make a big difference. I know >the inductance pull is not much, but that might not >be a good indicator. I've been doing some rough arithmetic >and it looks like the circulating currents in the ground >plane could add several hundred ohms effective series >resistance into the coil, thats enough to give Terry's >measurements. > >I'm just trying to get an estimate of how much it would >pull the coil inductance to see if that matches too. > >-- >Paul Nicholson, >Manchester, UK. >--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.