The A3848EEQ uses the dual criteria of frequency and amplitude for establishing a valid stop. Tuning accuracy (frequency criterion) is established by evaluating phase shift across the detector coil. The circuitry is similar to that used in FM discriminators. Because this detection system is phase operated, it remains effective even in the presence of strong signals, which can cause false stops in systems using narrow-band filters. The amplitude criterion for stop is determined by evaluating the IF level. It includes a unique circuit that removes the effect of the AGC action. This allows the AGC tuning components to be selected for low-frequency audio performance without compromising scanning speed.