Question

The Nyquist plot of a loop transfer function $G\left(j\omega \right)H\left(j\omega \right)$ of a system encloses the $(-1,0)$ point. The gain margin of the system is

• A. less than zero
• B. zero
• C. greater than zero
• D. infinity

Answer 1

The correct option is A less than zero

A system is unstable when Nyquist plot of $G\left(j\omega \right)H\left(j\omega \right)$ encloses the point $(-1+j0)$ and gain margin of unstable system is always negative or less than zero. Therefore, the gain margin of given system is less than zero.