In noise measurement the problem of noise transmission in the two-port networks in cascade is frequently met with. Each stage of the network itself will contribute its noise whereas it will Jose the noise power transmitted from the former stage. The noise can be exactly measured only when its loss and contribution in the network have been defined.This article analyses the loss and generation of noise in the network by means of the concept of the available power transmission coefficient

and derives the formula for noise transmission in the lossy . two-port networks in cascade. This formula has been applied to determine the available noise temperature of the thermal noise standard source.