Why do amplitude levels differ in optical transmitters between analog television and quadrature amplitude modulation (QAM) carriers?

The correct answer highlights that analog carriers incorporate a video sync pulse, which affects their amplitude levels. In analog television broadcasting, the video signal includes a sync pulse that is essential for maintaining synchronization between the transmitter and the receiver. This pulse ensures that the video frames are displayed correctly and in order on the receiving device. The presence of this sync pulse requires the analog signal to have a certain amplitude level to ensure reliable reception and synchronization.

In contrast, quadrature amplitude modulation (QAM) is a digital modulation technique that encodes information by varying the amplitude of two signals. QAM does not utilize a video sync pulse in the same manner as analog television. As a result, the amplitude levels for QAM carriers may be adjusted differently, often allowing for more efficient power utilization, since there is no need to maintain sync in the same way.

Understanding this distinction is crucial, as it highlights how the design and requirements of the signal affect the amplitude levels used in transmission.