There are 4 types of 50 Ohm impedance co-axial cable antenna connections which use the SMA (Subminiature version A) connections: SMA male has an internal screw thread with a pin in the center, SMA female is outside screw thread with a hole in the center Reverse polarity SMA male has an inside screw thread with a hole in … Continue reading SMA and RP-SMA 50 Ohm Co-axial Cable Antenna Connections Explained