On loop gain in linear networks

The paper clarifies the difficulties occurring in definition of loop gain in linear networks. The cut-insertion theorem allows one to obtain the parameters of the feedback system resulting from insertion into a cut the two-port providing preservation of the currents and voltages in the rest of the network. Using this theorem for different cuts one can describe the same network by different feedback systems. The characteristic equation of these systems is invariant, yet their loop gains are profoundly different. An example further analyses these difficulties. Some recommendations for the choice of the cut place and correct loading of the cut are given.