From: Paul
Date: Fri, 01 Sep 2000 20:35:49 +0100
Subject: Re: [TSSP] Mystery of the missing loss
Some further measurements from Terry. Terrell W. Fritz wrote: > First I measured the bare coil again just incase something > had shifted. > > Fo = 147.07 > Q = 50.89 > > A little shift and lower Q than before. I suspect this is due to the > condition of the ground plane deteriorating as I walk over the thin foil. Done pretty well that foil. I expect a ground plane might work quite well if placed underneath the carpet. > I set a Jennings vacuum variable capacitor to get the same frequency I > measured with a toroid. > C = 10.7 pF > Fo = 101.64 > Q = 60 > > The C value is telling of a problem. The wire I string to the cap has a > considerable capacitance to the ground plane. This capacitance is in > parallel with the vac cap. > > I repeated the 45 inch torroid to get a comparison and got. > > F0 = 97.154 > Q = 68.85 OK, thats good stuff. I'll respond to these results and others in another post. > I placed a 1/4 inch ring made from copper tubing around the > base of the coil. It was 12.5 inches in diameter and 4 inches > above the floor. > > Bare coil: > > Fo = 153.38 > Q = 53.63 > > Toroid on coil: > > Fo = 101.60 > Q = 80.89 > > The inductance of the coil without the ring was 75.0mH and 70.4mH > with the ring. Nice one, that provides a really useful calibration of loop coupling calculations, which I'm struggling with at the moment. > The ring seems to be adding a low loss energy storage element > to the system. Perhaps a complete circle ground plane does too. > Much as a capacitor stores energy as voltage, the ring stores > energy as current. Yes, and loses energy too I believe. More to follow on this in another post. Cheers, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.