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*To*: tesla-at-pupman-dot-com*Subject*: Re: New formula for secondary resonant frequency*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Fri, 02 Feb 2001 21:43:39 -0700*In-Reply-To*: <200102021055.KAA24592-at-abelian.demon.co.uk>*Resent-Date*: Fri, 2 Feb 2001 21:43:37 -0700*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <d4BClC.A.O1H.2x4e6-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net> Hi Paul, Fantastic formula for us computer type folks!! :-)) I also wanted to point out the dramatic affect Sonotube can have on such calculations. I inserted a Sonotube type form into my regular big coil form to see the differences it would make. http://hot-streamer-dot-com/TeslaCoils/Misc/SonoQ/SonoQ.jpg Using many toys, http://hot-streamer-dot-com/TeslaCoils/Misc/SonoQ/Stuff.jpg I scanned the coil's frequency response with and without the extra tube inserted. I swept the frequency linearly from 140 kHz to 150 kHz and measured the response with a whip antenna connected to the scope. The differences are shown at: http://hot-streamer-dot-com/TeslaCoils/Misc/SonoQ/SonoQ1.jpg With the second tube inserted into the center of the big coil tube, the frequency dropped from 147.2kHz to 146.68kHz. The Q dropped to 69.5% of the original. Although Sonotube is fairly good for coil forms, its loss can affect such details... Cheers, Terry At 10:55 AM 2/2/2001 +0000, you wrote: >Hi All, > >Calculator fiends may like to try out the following formula for >estimation of secondary resonant frequency. Applies to bare coils >(ie no top-load and no primary) in normal grounded-base configuration, >when situated over a reasonably well defined ground, with the coil >base not more than half the coil length above ground. > >Starting with: > > turns; > h = length of secondary winding, metres; > d = diameter of secondary - metres; > b = height of winding start above ground - metres; > awg = wire gauge, AWG; > > (metres = inches * 0.0254) > >Compute: > > x = h/d (form factor) > wd = 7.348e-3/pow(1.122932, awg-1) (wire diameter - metres) > sr = turns * wd/h (spacing ratio) > > fa = -94.6683*awg*awg*awg + 9000.55*awg*awg - 301175*awg + 3.64056e+6 > fs = 3.50662*sr*sr - 7.90171*sr + 5.83019 > fx = -0.000211179*x*x*x + 0.00557568*x*x + 0.0664809*x - 0.0153254 > t = fa * fs * fx/h/h > s = -3.85188e-15*t*t*t + 1.17176e-8*t*t + 0.631829*t + 482.463 > >and finally, > > fb = log( b/h/0.2) (use the natural logarithm) > Fres = s * (1.02 + fb/98.9065); (Hertz) > >Accuracy is around 2% average, with a peak error of around 4%. > >Some examples: > >My big CW coil: b=0.15, h=1.6, turns=725, awg=12, d=0.58; > Measured 90.9 kHz, formula 90.2 kHz, -0.8% error > >My half-coil: b=0.15, h=0.8, turns=365, awg=12, d=0.58; > Measured 150.7 kHz, formula 151.4 kHz, +0.5% error > >Terry's big coil: b=0.025, h=0.762, awg=24, d=0.2606, turns=1001; > Measured 148.4 kHz, formula 146.1 kHz, -1.5% error > >Marc Metlicka's >large h/d coil: b=0.3302, h=1.07696, awg=24, d=0.1081, turns=1700; > Measured 276.9 kHz, formula 276.9 kHz, 0.0% error > >The formula was derived by curve fitting to a database of around >1700 simulated secondary coils, and is expected to be more accurate >than estimates based on Medhurst capacitance. > >Regards, >-- >Paul Nicholson, >Manchester, UK. >-- >

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