center tapped inductor

I am buiding a group delay equalizer and need to make a center-tapped inductor using Micrometals' RF toroid. Anyone could give some ideas about how to make the winding and is there any requirement for the wire? Thanks!

Kan

A bifilar winding design is preferable in terms of leakage inductance, but has higher stray capacitance respectively lower self-resonance frequency.

I think FmV means to put two wires together and wind them simultaneously. Then connect end of one to the beginning of the second. It will provide you with good center-tapped coil. Depends on the application such wiring may works well up to 5 Ghz at least, but better not use it for so high frequencies unless you are very involved in broadband design. What is important it is to keep all wires that out of the core magnetic field as short as it possible.

FvM, RF-OM, Thanks!
What's the typical coupling coefficient between the coils? I guess should be close to one.

You are right, in this case it is practically 1.

I made one using the Micrometals RF toroid, but the coupling coefficient is very low, only around 0.5. How could this happen? Is there anything I need to care about of the winding? Thanks!

can you give a photograph of your inductor?. 0.5 Is too low, how you measured it?

Yes, 0.5 is too low. Please provide more information how you buit it and what is the frequency?

I guess that is wrong measurement...

Keep in mind the definition of coupling factor:
k = M/√(L1+L2)

For k ≈1:
Np*Ip=Ns*Is or Vs * Np = Vp *Ns

so If Np = Ns and k ≈1 then |Vp| ≈ |Vs| taking the center of tapped inductor as reference or ground.

Added after 1 minutes:

Ups...

k = M/√(L1*L2)

sorry.