# Re: Couples Therapy

```Hi Antonio,

After three months reading on The List and visiting the most beautiful and
impressive sites you come up with something like k=(b^2-a^2)/(b^2+a^2) ;-).
Thank you Antonio, I thought I was almost done and had to look out for the
black hole (I suspect myself to read a lot on The List to have an excuse not
to go to the garage and finish 'Catweazle 1')

Searching the net I stumbled upon 'Coupling Questions & coil measurements',
august last year on the site
http://w4dfu.ufl.edu/listarchives/1999/August/msg00225.html. (some
mirror???)'Magical K-values', remember Antonio? When I have more time I will
look into this matter. The formula reminds me (probably because of the +/-
bit) of the formula's to calculate the secondary frequencies of a coupled
bandpass filter when k > critical:
Flow = Fres / sqrt (1+k) and
Fhigh = Fres / sqrt (1-k)
and surprise surprise, these are the same as used to calculate 'the
bandwidth' of a TC!

better):

'Overcoupling is the moment that an inductive loose coupled bandpass filter
stops to increase the signal transfer and the bandpass is widened to form
two peaks in the dB/f graph (when k is increased from 0 to 1). This is on a
distinct point in the dB/f graph:
k < k-critical -> one freq-peak (fo),
k > k-critical -> two freq-peaks.'

> This condition would require explicit resistances in the circuit, and
> result in an extremely lossy Tesla coil.

I don't understand which condition would require explicit resistances in the
circuit.
Could you explain this to me or could you give me some reference where to
look?