Does the amplitude of the RF pulse affect the NMR signal?
V. approx explanation. The rf pulse is at 90$^\text{o}$ to the static field $B_0$ and has the effect of moving the magnetisation (sum of spin vectors) away from alignment along $B_0$ (z-axis normally) into the xy plane where it rotates and cuts through detector coils and induces FID signal. The FID can only be detected with a magnetisation component in the xy plane. The size of the rf pulse's magnetic field $B_I$ is proprotional to angle $\theta$ moved away from z-axis as $B_I\sim \tan(\theta) $ and so via magnetisation's component in xy plane (arrow on axis in sketch) to the size of the FID.