Phase-lock loop jump phenomenon in the presence of two signals

Conditions for the jump phenomenon in a phase locked loop which is preceded by automatic gain control in a tracking radar receiver are predicted on the basis of a nonlinear analysis. The jump occurs when the frequency separation of two sinusoidal signals at the input of the automatic gain control is greater than the bandwidth or the linearized loop. If the loop is initially locked to the stronger signal, the weaker signal will modulate the frequency of the voltage-controlled oscillator of the loop. The amplitude of the weaker signal can be increased until it becomes greater than the amplitude of the signal being tracked without causing the loop to lock. However, if the ratio of these two amplitudes is increased above some critical value, the loop will lose lock on the original signal, and jump to track the interfering signal.