# RE: Flat coils & undamped waves (was Wire Length)

```Original poster: "David Thomson" <dwt@xxxxxxxxxxxx>

Hi Kurt,

> 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

I did not see in your report where you measured the number of actual turns
and compared it to the calculated number of turns.

I have found that some of my flat spiral coils have 93% windings (loose) and
some have 97% efficiency (much tighter).  Also, were the measurements taken
before or after the coil was treated?  My experience is that the Wheeler
equation applies only to untreated coils.

> 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.

It is just as important to make sure the actual construction matches the
calculation method.  It doesn't do any good to calculate the turns per inch
based on ideal conditions, and then build the coil to a different structure.
Also, it matters if there are greater spaces in the outer part of the coil
than the inner part.  The outer part of the coil carries a greater
percentage of the inductance.

For flat ribbon wire, I am using 24 gage magnet wire rolled to a 4:1 aspect
ratio.  Although the windings are closer together, I account for that by
using the actual wire width in the calculation.

Although the turns are closer spaced (flat wire compared to round wire), the
coil is thicker due to the broadness of the wire, which is the same thing as
having parallel wound flat spiral coils adjacent to each other.  The
increased capacitance from the increased surface area and decreased distance
offsets by the decreased inductance from the equivalent parallel windings.

There are many factors, which we need to take into consideration for
producing a useful inductance equation.  I did not see these factors
accounted for in your report.

Dave

```