Off Center Fed (OCF) Antennas 50:250 ohm (5:1) Transformers Store/Antenna Products/CUBE Impedance Transformers (<1:1, 1:1, >1:1)/50:250 ohm (5:1) Transformers OCF antennas are very convenient as they will allow multiple bands of operation with a simple wire antenna which is fed off center with a 4:1 OCF Current balun with built in feed line choke,