Which frequencies are emitted by the Localizer on the left and right channels?

• A. 90 Hz on the left and 150 Hz on the right
• B. 150 Hz on the left and 90 Hz on the right
• C. 90 Hz on both sides
• D. 150 Hz on both sides

Answer: (A)

The Localizer uses two distinct amplitude-modulated tones to provide left-right guidance. The signal on the left side is modulated at 90 Hz, while the signal on the right side is modulated at 150 Hz. This arrangement allows the cockpit instruments to compare the relative strength of the two tones and indicate deviation from the centerline. When you’re on the centerline, the tones are received with equal strength; drifting to one side changes which tone dominates, guiding you back to center. Therefore, the correct pairing is 90 Hz on the left and 150 Hz on the right. The other options would misplace the tones or use the same tone on both sides, which would not enable proper left-right guidance.