*Question T8D01:
Which of the following is a digital communications mode?*  

*Correct Answer is  D: All these choices are correct*  

### AI Response: (may contain errors)  

The correct answer to the question is **D: All these choices are correct**. Here's why:

1. **Why the correct answer is correct:**
   - All the options listed (Packet radio, IEEE 802.11, and FT8) are indeed digital communication modes.
   - **Packet radio** is a digital mode that allows for the transmission of data packets over radio frequencies.
   - **IEEE 802.11** refers to a set of standards for wireless local area networks (WLANs), commonly known as Wi-Fi, which uses digital communication to transmit data.
   - **FT8** is a digital mode used in amateur radio for weak signal communication, utilizing a specific protocol for encoding and decoding messages.

2. **Why the other choices are incorrect:**
   - There are no incorrect choices in this case, as all options represent valid digital communication modes. Therefore, each choice contributes to the correct answer.

3. **Useful concepts:**
   - Digital communication modes are characterized by the use of discrete signals to represent information, as opposed to analog modes, which use continuous signals.
   - Common digital modes in amateur radio include:
     - **PSK31**: Phase Shift Keying for real-time text communication.
     - **RTTY**: Radio Teletype, which transmits text using frequency shift keying.
     - **FT8**: A specific digital mode designed for weak signal communication.

Understanding these modes is essential for the Extra Class exam, as they are widely used in modern amateur radio operations.