What signal is used to synchronize the coherent oscillator (COHO) to a fixed phase relationship with the transmitted pulse?

• A. Coherent oscillator lock pulse
• B. Coherent oscillator reset pulse
• C. Phase reference pulse
• D. Timing reference pulse

Answer: (A)

The key idea is keeping the radar’s coherent oscillator in step with the exact phase of the transmitted pulse. This is done by the coherent oscillator lock pulse, which provides a synchronization event that drives the COHO’s phase-locked loop so the oscillator’s output stays fixed in phase with the transmitted reference. When the lock pulse is applied at or near the pulse transmission, the COHO emerges with a phase that aligns with the pulse, enabling coherent processing of subsequent echoes and reliable Doppler measurements. Reinitializing or merely marking timing without this explicit locking action wouldn’t guarantee the continual phase coherence needed across pulses, and the other terms describe timing or generic phase references rather than the specific locking action to the transmitted pulse.