From: Paul
Date: Tue, 29 Aug 2000 21:56:26 +0100
Subject: Re: [TSSP] Q mesurements
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.