What is installed on the output of a QAM modulator to prevent intersymbol interference?

In the context of preventing intersymbol interference (ISI) in a Quadrature Amplitude Modulation (QAM) system, a Nyquist filter is essential. This filter is specifically designed to shape the transmitted signal in such a way that it confines the signal energy within a certain bandwidth while ensuring that the symbols do not overlap at the receiver.

When a Nyquist filter is employed, it allows for the optimal transmission of symbols over a given channel, thus maintaining the integrity of each symbol and preventing them from interfering with one another. This is crucial for maintaining the clarity and reliability of the received signal, enabling accurate data interpretation.

The prominent role of the Nyquist filter in filtering out unwanted frequencies and managing the timing of symbol transitions makes it a vital component in reducing ISI and improving overall system performance. Other options, while potentially useful in signal processing, do not serve the specific purpose of managing intersymbol interference in the same effective manner as the Nyquist filter does.