Abstract: A method and apparatus for accurately measuring the transfer function of a linear system or the linear part of a non-linear system. This is accomplished by using a spectrum estimation technique which utilizes a "transient random" stimulus consisting of a short burst of random signals applied to a system under test for a period of time that is shorter than the time used to measure a single spectrum. Thus the measurement period includes the time for the "transient random" burst and for the response of the system to substantially decya to zero. The spectrum measured over this period is used to form a first estimate of the transfer function. Other "transient random" stimuli, uncorrelated with the prior records, are then generated and the above procedure is repeated to achieve an average value for the transfer function estimate of the desired accuracy.

Abstract: A method and apparatus for obtaining an accurate measure of a transfer function of either a linear or the linear part of a nonlinear system. This is accomplished by utilizing an estimation technique using a "periodic-random" stimulus consisting of a random stimulus of a finite record length that is repeatedly applied to the system under test until the stimulus and the system response become essentially periodic. Once periodicity is achieved within the desired accuracy, a first estimate of the transfer function is derived from the measured spectrums of the stimulus and the system response. Another "periodic-random" stimulus, uncorrelated with prior records, is then generated and the above procedure is repeated to achieve an average value of the transfer function within the desired accuracy.