Why do amplitude levels differ between analog television and QAM carriers in optical transmitters?

The differentiation of amplitude levels between analog television and QAM (Quadrature Amplitude Modulation) carriers in optical transmitters primarily stems from the use of a video sync pulse in analog carriers to manage amplitude settings.

Analog television signals are designed with specific requirements for synchronization and amplitude. The video sync pulse ensures that the receiver can align with the transmitted signal correctly. This pulse provides a reference point that helps maintain consistent amplitude levels throughout the transmission process, ultimately resulting in a stable and clear video image.

In contrast, QAM is a more advanced modulation technique that encodes data by varying both the amplitude and the phase of the signal. While QAM does utilize synchronization techniques, it does not rely on a sync pulse for the same amplitude management as analog signals. Instead, QAM works by combining multiple amplitude levels and phase shifts to represent more data, which inherently leads to different amplitude characteristics when compared to traditional analog signals.

This fundamental difference in how amplitude is controlled is why the answer focuses on the role of the video sync pulse in analog carriers.