ABSTRACT
This chapter aims to develop H. W. Bode's feedback theory, which is applicable to the general network configuration and avoids the necessity of identifying the transfer functions µ(s) and ß(s). The procedure is difficult and sometimes virtually impossible, because the forward path may no be strictly unilateral, the feedback path is usually bilateral, and the input and output coupling networks are often complicated. Bode’s feedback theory is based on the concept of return difference, which is defined in terms of network determinants. The chapter shows that the return difference is a generalization of the concept of the feedback factor of the ideal feedback model, and can be measured physically from the amplifier itself. It introduces the notion of null return difference, which is found to be very useful in measurement situations and in the computation of the sensitivity for the feedback amplifiers.
