A previous publication by Carbal, see ibid., vol.18, p.719 (1976) analyzed the nonlinear space-time evolution of the electron cyclotron instability in a beam-plasma experiment. The interaction between a 2 KeV, 10 mA electron beam and the helium plasma so produced in a cylindrical chamber was studied. This note introduces a numerical method for temporal analysis of the nonlinear development of burst like instabilities, based on the determination of their time resolved k-spectra, whereby the second matching relation can be experimentally verified.