Introduction to Frequency Analysis

Cuthbert Nyack
Frequency analysis is based on the properties of the open loop transfer function G(s) in this case.
In the Bode plots 20 Log|G(jw)| and ÐG(jw) are plotted vs Log(w).
For the Nyquist plots Im(G(jw)) is plotted vs Re(G(jw)).
Both plots can be used to determine stability and phase and gain margins. Instability occurs when the Gain = 1 and phase = -180°
The Phase Margin is the difference in phase from -180 when the gain is 0dB. The Gain Margin is the difference (in dB) in gain from 0dB when the phase is -180°. Some of the applets show how the phase and gain margins are determined from Bode, Nyquist and Magnitude vs Phase Plots and how they are related to the Transient Response.
When enabled the following gif files show how some of the applets appear.

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COPYRIGHT 2006 Cuthbert Nyack.