From: "Terrell W. Fritz"
Date: Wed, 21 Feb 2001 18:20:23 -0700
Subject: Re: [TSSP] Problems with high elevation/small radius
Hi, I noticed too while working on E-Tesla that either having a top center connection or just a solenoid without and end wire makes a significant difference in f1. If a coil's diameter is large, there is a big air space at the top. Having a wire leading to that space can add a bunch of top capacitance. E-Tesla assumes that there is a center connection in all cases and thus there is a little spot in the field graphs that show this. http://hot-streamer.com/temp/CoilTop.jpg I guess we should always mention this in making precise f1 measurements. I did this automatically with my small coil testing but I just took this for granted that everyone knew why :-)) A wire to a center terminal can add several pF on a medium coil. I forget the exact differences but in E-Tesla where the frequencies are supposed to be "real close", the top termination is really critical. Cheers, Terry At 01:32 PM 2/21/2001 -0500, you wrote: >paul, everyone >i got to thinking about this stray capacitance dilemma and what i >wondered was that since my top turn curls into the center of the bare >coil for topload mounting, is this causing any added capacitance? >i first "QUICKLY" hooked my gen. radio bridge up to the coils 2 and 3, >over my ground plane on the milk crate. >i found that with the wire curled to top mount screw (nylon) it did give >a .8nf and .5nf higher c then with the wire extending straight up. >the leads were kept in the same config and i tried to sit exactly the >same while reading. >i then hooked coil 2 up for f1 readings. today, with wire curled to >screw, the f1 is 191.5 khz, with wire straight up, 193.3 khz. >again, probes and person as close to same as ?. >i'm not trusting the actual accuracy of the bridge values, but i see a >definite change of c from top turn when curled over the winding form. >??? >marc
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.