We were gifted a somewhat large (6"OD, 2.6" ID, 9/16" thick) ferrite core of unknown mix and original use. On face was marked 6.6uH w/4turns. My thinking it might make a good common mode RF choke on the output of an inverter generator or on coax feedline. Not familiar with properties of toroid cores of this size. Any ideas? 73, Mike AC5P