Originally Posted by Nikolas Ojala
Winding a 1:1 transformer would be simple using a bifilar winding. Inductive coupling would be near perfection. Parasitic capacitance is one thing to worry about. It depends on how you fill the bobbin. There will be parasitic capacitances series connected. If you had many small capacitances in series that would be better than small number of big capacitances series connected. Multi section bobbins may help. Wind one section full, then continue to the next, etc.
Inductive coupling is through the transformer core; bifilar winding does not change that.
Parasitic capacitance is typically not something to worry about when winding bifilar; on the other hand: it's your friend!
Good high frequency bandwidth is possible because of capacitive coupling which bifilar winding provides. But it only works that well with 1:1 ratio.