*Question E8B07:
Orthogonal frequency-division multiplexing (OFDM) is a technique used for which types of amateur communication?*  

*Correct Answer is  A: Digital modes*  

### AI Response: (may contain errors)  

Orthogonal Frequency-Division Multiplexing (OFDM) is a method used primarily in digital communication systems. Here's a breakdown of the question and the answer choices:

### Correct Answer: A - Digital modes

1. **Why the correct answer is correct:**
   - OFDM is widely used in various digital communication protocols, including Wi-Fi, LTE, and digital television. In amateur radio, it is utilized in digital modes such as PSK31, FT8, and DMR. These modes benefit from OFDM's ability to transmit data over multiple frequencies simultaneously, improving resistance to interference and multipath fading.

### Why the other choices are incorrect:

2. **B - Extremely low-power contacts:**
   - While low-power contacts can be made using various modes, OFDM is not specifically designed for extremely low-power operations. It is more about efficient data transmission rather than power levels.

3. **C - EME (Earth-Moon-Earth):**
   - EME communications typically rely on traditional single-carrier modulation techniques rather than OFDM. EME is focused on long-distance communication using high power and specialized antennas, which do not inherently require the multiplexing advantages of OFDM.

4. **D - OFDM signals are not allowed on amateur bands:**
   - This statement is incorrect. OFDM is permitted on amateur bands as long as the transmission adheres to the regulations set by the FCC and other governing bodies. Many digital modes that utilize OFDM are actively used by amateur operators.

### Summary:
- OFDM is primarily associated with digital modes in amateur radio, making choice A the correct answer. The other options either misrepresent the application of OFDM or incorrectly state its legality in amateur bands. 

Understanding the context and applications of OFDM will help you recognize its relevance in digital communications, especially in the amateur radio spectrum.