Cwlondon, if you want to understand common mode chokes, this should get you started:
http://www.butlerwinding.com/inductors/common-mode2.html
And yes, if you had a salvaged ferrite core, it is just two windings of few turns each, in opposite directions, one in series with the hot, one with the common. Here are some pictures. Could be made pretty cheap.
http://www.coilws.com/toroidal/Toroid_CM_Selection.htm
Ken
http://www.butlerwinding.com/inductors/common-mode2.html
And yes, if you had a salvaged ferrite core, it is just two windings of few turns each, in opposite directions, one in series with the hot, one with the common. Here are some pictures. Could be made pretty cheap.
http://www.coilws.com/toroidal/Toroid_CM_Selection.htm
Ken