What term describes a wide-bandwidth communications system with varying RF carrier frequency?

The term that describes a wide-bandwidth communications system with varying RF carrier frequencies is spread spectrum communication. This technique involves spreading the transmitted signal over a wider bandwidth than the minimum bandwidth required to transmit the information. This is primarily done for the purposes of enhancing resistance to interference and improving security against eavesdropping.

Spread spectrum systems can utilize various methods, including frequency hopping and direct sequence spread spectrum, to achieve this wide-bandwidth effect. The varying RF carrier frequency characteristic is fundamental to spread spectrum techniques as they change frequencies over time, making it difficult for potential interceptors to capture the signal consistently.

In contrast, frequency modulation (FM) changes the frequency of the carrier wave in accordance with the amplitude of the input signal, but it does not inherently involve wide bandwidth beyond what is necessary for the audio signal. Phase shift communication alters the phase of the carrier wave rather than varying the frequency extensively. Amplitude modulation (AM) focuses on varying the amplitude of the carrier wave and does not typically involve bandwidth spreading methods. Thus, spread spectrum communication is the correct term for a system that uses wide bandwidth along with varying RF carrier frequencies.