Abstract: This paper describes the concepts of diffraction, diffraction gain, diffraction loss, field strength at receiver due to knife-edge obstacles between the propagation path of the signal i.e. b/w transmitter and receiver. This paper also present the complete idea of identifying the position of obstacle in a Fresnel zone, diffraction loss, position of obstacle with varying distances b/w source and field and varying heights of obstacles in a Fresnel-zones represented by tabular forms and appropriate charts. The calculation, based on an approximate evaluation of the contribution of individual Fresnel zones to the total field, leads to the Fresnel theorem: the total field is just one-half that due to the first zone alone.