Consider the following Nyquist plots of loop transfer functions

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Consider the following Nyquist plots of loop transfer functions over ω = 0 to ω = ∞ . Which of these plots represents a stable closed loop system?

1. (1) only
2. all, except (1)
3. all, except (3)
4. (1) and (2) only

Correct Option: A

If GH plot incircles (– 1, j0) that is the critical point, then the system becomes unstable. So option 1 is there which does not enclose the (– 1, j0) other all are incircling the critical point.