Regarding ferrites - not to add any confusion, but Jack Smith of Clifton Labs (not any longer found in search) has done much testing with Steward cores (now Laird) Theses are available from Mouser and with a coating that provides protection for enameled wire when wrapped. These also appear to perform better than the other products usually found in homebrew equip.
Best John
attached, I hope, is one of Jack's discussion regarding ferrites and comparative data
