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

The coherent oscillator lock pulse is essential for ensuring that the coherent oscillator (COHO) maintains a fixed phase alignment with the transmitted pulse. This synchronization is critical in communication systems that rely on phase information to accurately decode the received signals. The phase relationship allows for coherent detection, which significantly enhances the signal-to-noise ratio and improves the overall performance of the system.

By locking the oscillator to the transmitted pulse, the system can effectively utilize phase modulation techniques and ensure that the waveform characteristics are preserved during transmission. This coherence allows for precise phase tracking, which is paramount in systems that depend on high-resolution signal processing.

In contrast, the other options do not facilitate this specific phase relationship. Frame sync typically refers to aligning the start of a frame of data rather than regulating the phase of a continuous wave signal. A trigger pulse may initiate certain events but does not specifically control the continuous phase coherence needed. A direct current (DC) modulator pulse is more related to modulating the signal rather than synchronizing the oscillator. Thus, opting for the coherent oscillator lock pulse is critical to achieving the necessary synchronization for coherent signal processing.