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On 10/14/20 11:10 AM, Douglas Johnson wrote:
What could one consider a good coupling starting point for a 3.5"
secondary? Even with the primary, maybe a little above or below?
Also, using tesla map, I see quite a difference in tuning by changing the
center hole size. Can someone explain this to me?
The coupling is determined by how much of the magnetic flux from one
coil (the primary) is in common with the flux from the other coil (the
secondary).
A primary with a giant hole has lower flux in the center than a primary
with a small hole - because the flux is distributed over a larger area.
Consider a vertical solenoid primary - that will have the highest flux
in the center, and is the highest coupling.
I think someone (Greg Leyh?) built a coil with a solenoid primary
*inside* the secondary.