Re: best coupling clearance

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <teslalist-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:

 > Original poster: "Christopher \"CajunCoiler\" Mayeux by way of Terry 
Fritz <teslalist-at-qwest-dot-net>" <cajuncoiler-at-cox-dot-net>
 >
 > Has anyone determined the best possible clearance between
 > primary and secondary for most efficient coupling?  Or has
 > there at least been a formula worked out?

The coupling is a complicated function of the geometry of both coils.
The values that lead to optimal coupling coefficients can be obtained
with a large number of possibilities, depending on the dimensions and
relative positions of both coils. There are good formulas that can
calculate the coupling coefficient as precisely as you can measure
it (or more...). Most of them (the precise ones) too complicated to
be confortably posted here. There are several computer programs
mentioned in  this list that can do the calculations, numerically or
using analytical formulas. One of them is my Inca program:
http://www.coe.ufrj.br/~acmq/programs/inca.zip
The calculation of the coupling coefficient considering low-frequency
operation, as done by the program, however, falls a bit out of the
reality, due to the distributed nature of the coils, specially of
the secondary coil. The effective coupling coefficient is usually a bit
higher that the calculated (or measured at low frequency).

An interesting note: A transformer with very high coupling and good
insulation can be built using a flat coil and a solenoidal coil,
both starting at a common ring. By increasing the radius of the
solenoid, while keeping the height of the solenoid and the width
of the flat coil constant, any coupling up to 1 can be obtained.

Antonio Carlos M. de Queiroz