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Re: Flat coils & undamped waves (was Wire Length)

Original poster: "Kurt Schraner" <k.schraner@xxxxxxxxxxx>

Hi Ed, Dave,

Ed, what you say about APPROXIMATIONS and limits on parameters of course is true. Here I was just meeting a case, were the limits for Wheeler were exceeded. The coil looks like this:


It can be seen, the ribbon to be made of really thin(0.55mm) and fairly wide(20mm) copper sheet. Initially I was having designed the coil for my UBTT TC, simply by Wheeler, by good luck adding a little safety margin for tuning. When the coil was finished, measuring the inductance by an LCR-meter, I noticed just beeing able to tune with almost the whole coil. The difference in L was about 17% vs. Wheeler. This led me to searching for the better formula in NBS circular 74, and implementing the procedure in an Excel.

Shurely, if the ribbon is less "pronounced", wheeler may give a good approximation.

Dave, what you may see from the above, I was having a realized spiral coil in front of me, on which I could measure the (DC resp. low frequency-)inductance, for each turn, with an LCR meter. I didn't need to "measure the number of actual turns and compare it to the calculated number of turns", but in fact did the same by tapping the physically existent turns for metering, and comparing the meter-result with the calculated L. Very simple indeed!

I also don't know, what you mean by

Also, were the measurements taken before or after the coil was treated?

As you can see, the uninsulated copper ribbon is in air, hold in place by acryl supporters. No other treatment!!! - In my view, which I think sharing with most of those following verified physics, the low f _inductance_ of a coil is mainly dominated by its geometry. When used for RF, of course, the self capacitance as well as the capacitances to the environment come to play.

I'm not ready to follow your other "theories", which are obscure to me.

Best regards


Tesla list wrote:
Original poster: Ed Phillips <evp@xxxxxxxxxxx>

Maybe I'm splitting hairs, but I have to disagree about the last
sentence, of Wheeler formula application for ribbon wire flat
spirals. Please see my 2004 TCML posting:


especially the 2 graphs:

To use the right calculation method can be crucial, when designing a
ribbon type flat spiral primary: the too high L prediction of Wheeler
may lead to a too small primary construction.


   Wheeler's APPROXIMATIONS were presented as exactly that, with
explicit  limits on parameters and the associated accuracy.  This
last part sometimes gets forgotten, leading to erroneous
results.  The correct Wheeler formula applied with the correct
dimensional limits gives good accuracy.