Analysis of a Tuned Coupled Circuit by Root-Locus Techniques

Application of root-locus techniques to the familiar transformer-coupled tuned circuit accurately locates the poles of the transfer function as a function of the coefficient of coupling, thus enabling the frequency response to be found easily by graphical zero-pole techniques. The locus is seen to be a circle centered on the negative real axis, and this explains the fact that the lower frequency peak in the undercoupled case is greater than the higher frequency peak, a phenomenon which is not explained by the usual algebraic approximations. This ties theory and experimental results together nicely and gives an engineering student motivation and practice in the use of root-locus techniques in circuit analysis.