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Re: Propagation velocity in long helical coils.
Hi Robert, all,
On 17 May 00, at 20:36, Tesla List wrote:
> Original Poster: "Robert Jones" <alwynj48-at-earthlink-dot-net>
>
> Hi Terry and all,
>
> As you can read my mathcad files thats going to be helpful. I suggest you
> start with the zero internal C version as thats the one I have the equations
> for. Also I have not included ground reflections or top load mag
> reflections. The ground reflections may be important for end effects at
> least thats what Malcolms measurements indicate. When you or Malcolm has
> some comparative L measurements on the ground and isolated we will know more
> about it. You will also need inverse FFT. As in many of these types of
> problems you solve the transformed equation then convert back to get the
> answer you wanted. One more thing I assume you have complex FFT routines
> i.e. unless its a symmetric bipolar coil you need the sin and cos terms. Or
> I can add the ground reflection for symetry that probaly best but a bit more
> work on the equations and we need those measurments as a check on the
> reflection equation.
>
> Could Malcolm get hold of Wheeler's paper for his L formula so we can check
> its got no inapprorate assumptions ie it is valid for short coils.
I will look for it tonight. However, his formula has proved to be
"pretty good" for all the single layer coils I have ever measured,
short, fat long etc.
Also, you asked about L with regard to ground proximity. The
best test I can think of would in fact be to measure L with and
without a substantial topload present. I will also arrange to do that in
my 10" coil (see the post I've just sent). Unfortunately concrete
floors are less than perfect conductors. I can say from expts I've
done in the past that self capacity is by far the most affected
quantity from proximity of nearby objects since it is coupling into
them via what is essentially an open field. Sound resonable?
<snip>
Regards,
Malcolm