From: "Terrell W. Fritz"
Date: Thu, 31 Aug 2000 19:49:51 -0600
Subject: Re: [TSSP] Mystery of the missing loss
Hi Paul, 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. > >Some possible experiments: > >1/ Split the ground plane. Already tried. Q went down, > score: E one, B nill. > >2/ Replace the toroid with a 25pF capacitor wired back to the > central ground point. This will have a much lower Rct than > 130 ohms. The toroided f1 should be reproduced, but if E > return loss is significant, a higher Q factor should be > obtained. 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 > >3/ Extend the foil ground plane to catch more of the > external flux. See if the Q goes up. I don't have an easy and 'scientific" way to do this. the ground plane's condition is also probably a factor now. > >4/ Tightly couple a shorted turn near the base of the coil > to artificialy add extra eddy current loss, and see if > the two Q factors diverge further. > 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. 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. I am not sure I have great trust in further experiments with the ground plane. It is starting the shred and such. No longer a stable element... Cheers, Terry >I'm sure there must be some cunningexperimental tricks to >decouple these two potential sources of loss, and if we can >do so unabmiguously then that would be a great step forward. > >Regards All, >-- >Paul Nicholson, >Manchester, UK. >--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.