*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 technique used for digital modes in amateur radio communication. Here's why:

1. **Correct Answer: Digital modes (Choice A)**
   - OFDM is a method of encoding digital data on multiple carrier frequencies. It is widely used in digital communication systems because it efficiently handles multipath propagation and is robust against interference. This makes it suitable for digital modes in amateur radio, such as digital voice and data transmissions.

2. **Why the other choices are incorrect:**
   - **Extremely low-power contacts (Choice B):** While OFDM can be used in low-power scenarios, it is not specifically designed for extremely low-power contacts. Techniques like QRSS or WSPR are more commonly associated with extremely low-power operations.
   - **EME (Earth-Moon-Earth) (Choice C):** EME communication involves bouncing signals off the moon and typically uses modes like CW (Morse code) or JT65, which are optimized for weak signal conditions. OFDM is not typically used for EME due to its complexity and the specific requirements of EME communication.
   - **OFDM signals are not allowed on amateur bands (Choice D):** This statement is incorrect. OFDM is allowed on amateur bands and is used in various digital modes, such as those found in digital voice and data systems.

In summary, OFDM is a versatile and efficient technique for digital modes, making it the correct choice for this question.