This shows a competitive typical Full Duplex RFID system. Because the reader is always transmitting, the associated noise can be a problem. Full Duplex means that signals travel in both directions at the same time. The reader block diagram shows that the primary winding is part of the reader's resonant antenna circuit while the secondary winding is part of the transponder's resonant circuit. Also, shown are the transmission signal waveforms for the reader and transponder. To communicate, the reader creates a powerful carrier signal which causes the transponder’s resonant circuit to oscillate. These oscillations create an oscillating magnetic field which is amplitude modulated by the transponders control circuitry and used to send data back to the reader.