What signal modulation technique do cable operators use to transport digital television signals?

Cable operators utilize Quadrature Amplitude Modulation (QAM) to transport digital television signals effectively. This technique combines both amplitude modulation and phase modulation, allowing for the transmission of large amounts of digital data over a single channel.

QAM works by varying both the amplitude and the phase of the signal. By using different combinations of these variations, QAM can encode multiple bits of information per symbol, improving the efficiency of data bandwidth. This makes it particularly suitable for digital television and broadband data services, where high data rates are necessary.

Unlike other modulation methods such as Amplitude Modulation (AM), which can only carry analog signals and has lower efficiency, or Frequency Shift Keying (FSK), which transmits data based on variations in frequency and is less efficient for bandwidth-intensive applications, QAM strikes a balance that is optimal for cable operators. Phase Shift Keying (PSK) is effective for certain digital communications but typically does not utilize the amplitude variations that make QAM such a robust choice for high-capacity data transmission required in digital television.