Yup! Amidon BN-73-202 (Fair-rite 2873000202) is good stuff! Very high permeability. W8JI himself kindly introduced me to 73 material back in the 1980s. Back then we just used Beverage antenna transformers made from stacked ferrite beads made from that that stuff, but those binocular cores were far superior.
630m is ~475 kHz, and 73 material works (to a degree) down to 100 KHz. www.w0btu.com/Beverage_antennas.html#Beverage_Antenna_Transformers I just bought 100 of those cores from Newark. Cheap! I still have to test them (as I always do) but I've never run into those that didn't meet specs. FYI, Chuck Hutton has a better grasp on the technical aspects of ferrite that I do. 73, Mike www.w0btu.com _________________ Topband Reflector Archives - http://www.contesting.com/_topband