What is Side tone coupling? Explain with circuit diagram.   Simplex communication :in telephone communication only two entity is involved one is transmitting(talking) and one is receiving(listening) is known as simplex communication. Half-duplex communication:  in communication information transfer in both ways but not a simultaneously is known as the Half-duplex communication. Full-duplex communication: in communication information transfer in both ways  simultaneously is known as the Full-duplex communication. Side tone coupling :  In telephones, it is the hearing of one's voice in the receiver when one speaks. Too much  side tone  make people speak lower and can cause feedback. Too little  side tone  and people may think the phone is not working or may shout.                                  Fig:  Smooth Tone Clickless CW Sidetone Generator                                      Fig: Schematic diagram of the sidetone circuit Figure Description: