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

["Tesla list" <tesla@xxxxxxxxxx>]

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:

http://twfpowerelectronics.com/~kurt/UBTT/FlatPrim_1555.jpg

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

Kurt


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:
>
> http://www.pupman.com/listarchives/2004/October/msg00018.html
>
> especially the 2 graphs:
> http://home.tiscalinet.ch/m.schraner/Lstrip_Wheeler.gif
> http://home.tiscalinet.ch/m.schraner/Lstrip_NBS.gif
>
> 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.
>
> Kurt"
>
>    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.
>
> Ed