Regeneration Theory and Experiment

A comprehensive criterion for the stability of linear feed-back circuits has recently been formulated by Nyquist, in terms of the transfer factor around the feed-back loop. The importance of any such general criterion lends interest to an experimental verification, with which this paper is primarily concerned. The subject is dealt with under five principal headings. The first section reviews some of the criteria for oscillation to be found in the literature of vacuum tube oscillators. The second describes the derivation of Nyquist´s criterion somewhat along the lines followed by Routh in one of his investigations of the stability of dynamical systems. The third part deals with two experimental methods used in measuring the transfer factor. The fourth is concerned with the particular amplifier circuit used in the test of Nyquist´s criterion. The last section applies the criterion to a nonlinear case, and to circuits including two-terminal negative impedance elements.