Tesla's "COIL FOR ELECTRO-MAGNETS".

[MileHigh]

The real shocker is that Walt Disney and Nikola Tesla have a thing going on!!!!!   

[gyulasun]

Hi TinselKoala,

the fact remains: you get out what you put in, minus losses.

I would refer to a paper from Nichelson (you may have read it: http://home.comcast.net/~onichelson/VOLTGN.pdf ) where he also tested two coils, albeit they were not pancake but solenoid types (it does not matter though as Tesla wrote). Nichelson measured the voltage gain for the single wire and the bifilar solenoid coils and found the voltage gain of the bifilar coil was 5.39 times higher than that of the single wire coil while the calculated voltage gain gave 0.57 times as high only.
You can see the measured voltage gains, plotted on a scale of 0 - 1 for both coils in the figure below from the above paper: the bifilarly wound coil has Vin/Vout ratio of 0.98 at 11 MHz self resonant frequency while the single wound coil has Vin/Vout ratio of 0.18 only, at 19 MHz self resonant frequency.

So his findings (Vin/Vout=0.98 for the bifilar) can confirm your above quote, unfortunately  . Among some questions I consider one question maybe the most interesting: how the single wire solenoid (or your single pancake) would perform if it were tuned to the same frequency the bifilar coil has its own self resonant frequency (11 MHz in the above example), by using a suitable tuning capacitor in parallel with the single coil?  Somehow I "feel" the bifilar coil would still win (by not much though) due to its distributed type 'tuning' capacitance, albeit wire insulation (dielectric qualities) may also have a role in that.
Any chance you may dig out those 'ingredients' from 2008 for some more tests on the two pancakes?

Thanks, Gyula

[TinselKoala]

Unfortunately those coils are in Canada and I'm not. So I'll have to make a new bifilar to match the pancake I already have. I did do some tuning tests with air variables on those older coils but nothing really quantitative, and I can't really recall anything coherent about that testing now. But I'll be working on the issue over the next several days, and I'll let you all know what I observe.

[MileHigh]

Gyula,

I have never played with a network analyzer like the HP3577B.   The closest I ever came to that was playing with a frequency spectrum analyzer.   It appears to be a device that puts out an excitation signal which typically will sweep a sine wave over a given frequency range on an output port.  Then on an input port it will record the response to the excitation and produce things like gain and phase plots.  In the spec sheet they mention how a typical application might be to measure a filter response and make sure the attenuation at a given excitation frequency is within some kind of programmable tolerance.

I am under the impression that the output port is 50 ohms and the input port is either 50 ohms or it is high impedance.  However, from the spec sheet I read it was not clear for me.

All that being said, I have "issues" with the paper and suspect that yet again, it's the people that are writing the paper that are the issue and not the equipment itself.

For example, when they talk about the "gain" they seem to be implying an impedance divider network where the coil is one element and a one ohm resistor is the other element.  Of course there is no one-ohm resistor anywhere to be found and no impedance divider network.

Then, what they refer to as the "calculated voltage gain" for each coli is in fact nothing more than the impedance of each coil in "reactive ohms."

Then, they use the measured resonant frequencies of each coil for the "voltage gain" calculation.   Since the "calculated voltage gain" for each coil is nothing more than the reactive impedance for each coil where each coil is modeled as a pure inductor only.  But when you start talking about resonant frequencies you are _not_ talking about a pure inductor only, you are talking about a series or parallel LC circuit.

Then when they discuss the ratio bifilar/single they are comparing the impedance ratios of two pure inductors at two frequencies.  Back to the same conundrum of mixing pure inductance with two different frequencies that are based on LC resonance.

I am not feeling it for that paper at all.  I am seeing some amateurs playing with a sophisticated network analyzer and crunching numbers together that don't really make any sense.  That's a phenomenon that I have seen several times before.

I have no doubt that the HP network analyzer will show distinct differences between the two types of coils.  However, the "voltage gain" number crunching that they did in that paper does not smell right to me at all.

Going back to TK's experiment, there at least he is in the ballpark for finding differences between the two types of coils.  He is using a spark gap so that's exciting the coils with a lot of high frequency content and there indeed, the capacitance can and will come into play.  That's distinctly different from imagining that a series bifilar coil is going to make a big difference in the operation of a pulse motor.

MileHigh

[TinselKoala]

I can't argue with that either.