From: Paul
Date: Wed, 30 Aug 2000 11:33:47 +0100
Subject: Re: [TSSP] Q mesurements
Another set of Q measurements from Terry. Terrell W. Fritz wrote: > 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 ;-) Yup, I dont think it matters RMS or peak so long as you keep to one or the other. > 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. OK, we expect it to pull the frequencies around a little, no problem so long as its all stable during the run. 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 Qualitatively different now, the toroided coil now has the best Q, so somethings changed. Q factors are more realistic now. Ultimately I think we should be seeing 150 to 200 at least. > I then took my trusty knife and slashed my foil ground plane > right down the center with only the center connecting both > halves... ...expecting a significant improvement, now that the longest and therefore the heaviest coupled current loops are broken... > 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 Aargh! Both Q factors have gone down in the same ratio, when they should have gone up! Frequencies have not altered much so the basic geometry was unchanged by the cut - good, but they've gone down slightly rather than up - puzzling. > I remeasured the secondary's inductance at 75.1mH. Good, the inductance has increased slightly from the original measured 74.1mH, which is consistent with splitting the ground plane, but the frequencies have gone down! > Looks like the measurements are going a little opposite to > what is predicted. I assume that just makes it more > interesting and fun :-)) Gosh, you're right about that! Usually means we're about to learn something. This'll certainly take some explaining, right now I'm at a loss (excuse pun!). Cheers, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.