A rule of thumb:
If a toroid is painted all over, it is powdered iron.
If a toroid is black, but not painted, it is ferrite.
If a toroid is covered with a form fitting plastic case,
it is a ribbon steel.
-Chuck Harris
Charles wrote:
...An unknown green one saturated too soon and required very few turns - must be an
iron powder one with high permeability. Finally a 3/4" yellow core (72 turns to get
to 250 uH, that was tedious) worked at the original frequency and didn't cause
trouble unshielded :)
