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*To*: tesla@xxxxxxxxxx*Subject*: RE: Flat coils & undamped waves (was Wire Length)*From*: "Tesla list" <tesla@xxxxxxxxxx>*Date*: Fri, 19 Jan 2007 21:19:39 -0700*Delivered-to*: testla@xxxxxxxxxx*Delivered-to*: tesla@xxxxxxxxxx*Old-return-path*: <tcmlmod@xxxxxxxxxxxxx>*Resent-date*: Fri, 19 Jan 2007 21:19:38 -0700 (MST)*Resent-from*: tesla@xxxxxxxxxx*Resent-message-id*: <tjJ6aP1QdQK.A.qtE.ahZsFB@chip1>*Resent-sender*: tesla-request@xxxxxxxxxx

Original poster: "David Thomson" <dwt@xxxxxxxxxxxx> Hi Ed, > > > Answer to your question is that "inductors are inductors" no > > > matter what the shape and flat spirals have no special and desireable > > > electrical properties. ... > Too much to comment on in one note. Of course the geometries > make a difference, the question is whether one is superior to the > other and I voted for the solenoid. Neither coils is superior to the other. They both have different uses. It is a matter of applying the right coil to the right usage. If your goal is to spill electrons all over the place with a spectacular display, and you plan to use only one coil, then yes, the solenoid would be your choice. However, some people are a little more sophisticated and choose to investigate the many different qualities of coils. > I can't understand how the flat > spiral can rise in frequency with the epoxy coating and find it hard > to believe. The flat spiral coil is naturally disposed to lower potentials and higher currents than is the solenoid coil. This is the inherent difference due to their geometries. When coating is first applied to a flat spiral, instead of increasing the capacitance, the dielectric causes the potential to increase, thus raising the resonance. With a solenoid coil, the potential is already maxed out so that coating it increases the capacitance, and thus lowers the resonance. I just performed these measurements last week. I used the Wheeler equation and resonance equation to predict how many turns will produce a flat spiral coil of 299kHz. The equation was spot on. I verified this using a frequency generator. I also wound a tall solenoid to the same resonance and tested it. Both coils were resonant with each other. Then I coated the flat spiral and insulated the tall solenoid. The flat spiral coil increased to 430kHz, the tall solenoid dropped to 280kHz. I spent two days constantly rechecking the measurements and working out the mechanics involved. If you don't believe it, try it for yourself. As a result of the above experience, I have had to wind a new flat spiral coil. This time I wound it to .753 of the target frequency, anticipating that insulating the coil will bring it up to the frequency I want. > Haven't tried it myself so am no expert. Normally these roles are reversed between us. > I'm not sure what you mean by "greater range of resonance" - > that's not a familiar term. Depending upon the treatment of the coils, all things being as equal as possible, a tall solenoid could have a resonance range of 15kHz, while a flat spiral coil of similar dimensions would have a range of 30kHz. You were just having a discussion with Gary Peterson on spread spectrum coils. A wide resonance range is not the matter you were discussing, but a coil with a wider resonance range could certainly resonate at more frequencies than a coil with a narrower range. Tesla could easily have transmitted several different frequencies simultaneously on a flat spiral secondary system. Once again, this is something you can check for yourself. Wind a flat spiral coil and a solenoid coil to the same resonance. See how broad their peaks are. > As for lower potential and higher > current, that is a function of the surge inpedance of the circuit and > not the geometry of the inductor. For the same L/C ratio the > performance should be the same. If you wind flat spiral and solenoid coils with the same gages of wire, and with the same average radius and wire length, you will find not only are the potential/current ratios different, but also the inductance/capacitance ratios are different, too. Similar coils with different geometries *do not* have the same L/C ratio. Without even building the coil, and using just a coil modeling program, you can make these calculations and see for yourself. Coil geometry *does* make a difference. Dave

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