What are two common types of spread spectrum systems used in RF communications?

Frequency Hopping and Direct Sequence are indeed two common types of spread spectrum systems used in RF communications.

Frequency Hopping Spread Spectrum (FHSS) works by rapidly switching the carrier frequency among many different frequency channels, using a spreading code to determine the sequence of frequencies. This method helps to minimize interference and enhances security since the signal is spread over a range of frequencies that change quickly, making it more difficult for eavesdroppers to intercept it.

Direct Sequence Spread Spectrum (DSSS), on the other hand, spreads the signal over a wider bandwidth by modulating it with a pseudo-random noise sequence. This technique results in a signal that appears as wideband noise and provides resistance to interference and jamming. The key characteristic of DSSS is that it allows multiple users to share the same frequency band without significant interference as each user transmits with a unique spreading code.

The other options involve modulation methods that do not qualify as spread spectrum techniques. Amplitude Modulation (AM) and Frequency Modulation (FM) are standard modulation methods and do not involve the spreading of signals over a broader bandwidth. Similarly, Single Sideband (SSB) and Continuous Wave (CW) are also traditional modulation schemes used for conveying information and do not fall