Frequency Response Displayed in Real Time

For the purpose of classroom and laboratory demonstration of linear system frequency response, the technique of applying a sinusoid of linearly varying frequency is especially dynamic. Here the restrictions on frequency sweep rate and observation time for which the envelope of the output signal is the system frequency response are clearly developed. It is shown that for such restrictions the output is a sinusoidal of frequency (ω+ºt) with instantaneous amplitude |G(j[ω+;2αt])|.