Who knows what this ferrite cylinder is from ? I got this decades ago from somewhere. I don't think there were many clues with it. 

As for frequency response - many years ago i put a 2 turn winding on it. I swept it with a dipmeter and it just about pulled the meter's pointer off its face - so the ferrite material is not strictly for low frequency.

If i remember vaguely, this may have come off some kind of microwave tube ??

Your input ?

-Hue Miller