In message , Ken
writes
I may be obsessing.

When putting trifilar winds around a toroid, does it matter how the
three wires are twisted before they are wound?

The easiest way is to just twist the two "outside" wires around the
"center" wire. The outside wires would wind up a little longer. It
would just a moment longer to plait or braid them, which would make
them equal length. Does it matter?

Ken KC2JDY


Ken
(to reply via email
remove "zz" from address)

From my experiences with winding small torroids for CATV, the bandwidth
(at least at the HF end) definitely better when you interwind
(interleave) the windings.

We put this down to the fact that it probably minimises the capacitance
between the turns of the same wire. For example, suppose you use red,
green and blue wires. As you progress around the circumference, you have
a regular sequence of red, green, blue - red, green, blue etc etc. You
will never have a red adjacent to a red etc.

Note that, in principle, you could wind bifilar and trifilar using bare
wire, and (with care) never have the adjacent turns touching.

One manufacturer used to use special bifilar and trifilar wire (like
miniature flat twin (and triple).

If you do want to twist, we found that twisting the wires would give you
a more consistent (and lower) characteristic impedance. This is probably
because, if the wires are kept in good contact with each other, the
capacity per length is consistent. However, there is no point in
twisting any more than is sufficient to keep the surfaces of the wires
in intimate contact.

I never thought of braiding (also called 'platting' in the UK). Sound
like hard work to me!

Ian.

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