Bill, Photos of the common-mode choke at the base of mine ( http://www.w0btu.com/160_meters.html#inv-l_antenna) are at http://www.w0btu.com/files/antenna/160m_inv-L It's 6 turns of F-6 coax through four 2.4" OD Fair-rite #31 cores ($7 each from Mouser), per K9YC's PDF. 73, Mike www.w0btu.com