[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

*To*: Tesla List <tesla-at-pupman-dot-com>*Subject*: Re: Resonator Self Resonant Frequency*From*: harvey norris <harvich-at-yahoo-dot-com>*Date*: Mon, 12 Jun 2000 18:21:08 -0700 (PDT)

--- Tesla List <tesla-at-pupman-dot-com> wrote: > Original Poster: "Malcolm Watts" > <malcolm.watts-at-wnp.ac.nz> > > Hello Harvey, > > > Original Poster: "harvey norris" > <harvich-at-yahoo-dot-com> > > > > > > --- Tesla List <tesla-at-pupman-dot-com> wrote: > > > Original Poster: "Malcolm Watts" > > > <malcolm.watts-at-wnp.ac.nz> > > > > > > Hi all (especially those interested in resonator > > > resonant frequency), > > > > > > In poking around the web a bit I came > upon > > > this url which gives > > > some information from the list archives on this > > > subject. I referred to > > > this some time ago. I have tested the formula Ed > > > Harris gives on a > > > coil I often refer to when discussing coil > > > characteristics and it works > > > well: > > > How did you test it? Using fiber optic probe leads as Terry has done?http://www.pupman-dot-com/listarchives/1996/june/msg00227.html > > > > > > Regards, > > > Malcolm > > > > > My calculations show a little more deviance from > > quarter wavelength value, about 35% in the cited > case > > below. Ed Harris' info follows, where I rewrote > the > > formula to avoid ascii problems. HDN > > > > If you are just interested in computing > self-resonant > > frequencies there is another method which I have > found > > useful and generally accurate to about 10% for all > > coil sizes - space wound or not. Its limitation is > > that it probably shouldn't be used for aspect > ratios > > (Height/Diameter)<1 due to the assumptions of the > > original derivation. > > Freq=29.85 *{the fifth root of H/D}/[N*D] > > > > where > > F= self resonant frequency in Mhz of an 'isolated' > > coil > > H= coil height in meters > > D= coil diameter in meters > > N= total number of turns > > > > Applying the formula to 31 inches,[or .79 meters] > of > > 20 inch diameter, or [.52 meter] Sonotube only > yeilds > > a H/D of 1.52, not a good ratio for a tesla > secondary, > > however two were built for a possible future > bipolar > > application. The other unusual parameter in > applying > > this formula to my first coil attempt some years > ago > > was that I used #14 gauge wire for the secondary, > > only yeilding 9 turns/inch or a low 280 for the N > > figure. So I thought the list might be interested > to > > find how this formula stacks up to the quarterwave > > length consideration that is ALWAYS used to my > > knowledge to find the resonant frequency of a > > secondary single layer wind air core without a top > > load capacitance. > > What quarterwave length consideration? The wire? Bad > choice. I've > expalined why on a number of occasions. This may have been before I was on the list. If you can point me to any particular month in the archive, I can study this better. I dont think the archive has an Author list. > The only further obfuscation in that > > case then becomes the Medhursts approximations of > > internal capacity made by geometry of the inductor > > expressed as different H/D ratios. I have not > > consulted this chart for this case as I fomerly > > thought I had found that its influence was minimal > on > > this case, which I have a point of confusion here > > also, if the spacing between wires is what > consists of > > internal capacitance, which is then why little > exists > > for this case of 9 turns per inch, then why does > the > > geometry expressed as the H/D exist as a > predominat > > factor in determining that internal capacitance? > > Because wire spacing doesn't govern the dominant > capacitance. > Actually this opens a can of worms. It has been > argued (rightly in > my opinion) that self capacitance is something of an > artificial > construct used to explain the distribution of charge > on a structure > (or something similar). I believe the Corums have > something to say > about this in a forthcoming work where the topic of > Cself is > discussed. Sort of like defining the speed of light > in terms of > permeability and permittivity. Speaking strictly of > coil capacitance in > the sense in which we understand it, it is most > likely a function of > surface area of the structure but that is probably > not the whole story. This seems like a proper interpretation for C intrinsic, it does seem like surface area must have a lot to do with it. > > Getting on with the comparison, I used 3 500 ft > spools > > for a total of 1500 ft which yeilds a quarter > > wavelength of .28 mile. Thus one cycle occurs in > 6.1 > > Us in which the reciprocal of this is around > 163,600 > > cycles per second. Applying the above given > > information in meters to the above formula where > the > > fifth root of 1.52 is given as 1.086 yeilds around > > 222,600 hz in my calculations. This seems a little > off > > for a 10% quoted figure of accuracy. > > fomula only applies for thinner gauge wire Calculating for double the length of wire yeilds 128,000 hz where a 1/4 wavelength value would be around 82,000 hz. That H/D of 3 is a more conventional ratio, so if this is true best frequency to resonate a bare coil then would be the higher figure, correct? Doesnt this sort of trash the quarter wavelength premise? > If you actually build the coil you will find that > Ed's formula is correct. > I posted a couple of months ago pointing out the > huge disparity > between trying to use apply the free space > wavelength to a piece of > coiled-up wire. It doesn't work and never has. I dont quite follow here. All the old texts always cite the quarter wavelength of the secondary as the factor to tune the primary to. Adding a top load changes that also to a lower freq. And the Medhurst charts give another internal capacity to be considered for the best primary capacity to be used. Now it has also be found that larger than resonant values for that capacity will work well, if I understand things correctly. If that is true then doesnt it mess up the former understandings? Pardon the ignorance but I am trying to fathom what is being stated on the list by others concerning this issue. > > Make sure the top line reads " (H/D) to the 1/5 > power" > > Note that the frequency is a very weak function of > the > > aspect ratio (H/D), but a fairly strong function > of > > the number of turns and the diameter. This is an > > adapation of the formula for Helical Antennas > found in > > Reference Data for Radio Engineers as well as in > the > > section on slow wave structures in "Fields and > waves > > in Communication Electronics" by S Ramo, J R > Whinnery, > > and T D Van Duzer. A form of this equation also > > appears in both of the Corum brother's books: > "Vacuum > > Tube Tesla Coils" and "TC Tutor" Incidentally, the > > Corums incorrectly attribute the analysis of the > helix > > to Kandoian and Sichak. These guys actually just > made > > a simplification of the formula reported earlier > by JR > > Pierce (1947) and Franz Ollendorf (1925) and even > more > > amazing : Pocklington (1897) (see below). > > > ------------------------------------------------------------------ > > I have a list which has more complete references. > -Ed > > Harris > > > > Thanks Malcolm for posting the URL, just wanted to > > point out a possible discrepancy involved with > > relative low N values. > > Sincerely HDN > > I can do no better than suggest that a measured > result is better than > a calculated one. > > Regards, > Malcolm > > Can you breifly describe how those measurements were made or direct me to an archive date? HDN ===== Binary Resonant Systemhttp://www.insidetheweb-dot-com/mbs.cgi/mb124201 __________________________________________________ Do You Yahoo!? Yahoo! Photos -- now, 100 FREE prints! http://photos.yahoo-dot-com

- Prev by Date:
**MOT Ballast for Pole Xfmr** - Next by Date:
**MOT Ballast for Pole Xfmr** - Prev by thread:
**Re: Resonator Self Resonant Frequency** - Next by thread:
**async RSG question** - Index(es):