*Question E2E01:
Which of the following types of modulation is used for data emissions below 30 MHz?*  

*Correct Answer is  B: FSK*  

### AI Response: (may contain errors)  

The correct answer to the question about modulation types used for data emissions below 30 MHz is **B: FSK (Frequency Shift Keying)**.

### Explanation of the Correct Answer:
- **FSK (Frequency Shift Keying)** is a method of digital modulation that conveys data by changing the frequency of a carrier wave. It is widely used for data transmissions below 30 MHz, particularly in amateur radio and other communication systems. FSK is effective for low-bandwidth data communications and is robust against noise, making it suitable for the HF bands.

### Why the Other Choices are Incorrect:
- **A: DTMF tones modulating an FM signal**
  - DTMF (Dual-Tone Multi-Frequency) is primarily used for telephone signaling and is not a modulation scheme for data emissions. It involves sending two simultaneous tones, which is not suitable for general data transmission below 30 MHz.

- **C: Pulse modulation**
  - Pulse modulation refers to a variety of techniques where the signal is represented by pulses. While it can be used for data transmission, it is not specifically designed for the typical data emissions below 30 MHz, making it less common in this context.

- **D: Spread spectrum**
  - Spread spectrum techniques, such as frequency hopping or direct sequence, are used for secure and robust communications but are generally not classified as a modulation type for standard data emissions below 30 MHz. They are more complex and typically used in specific applications like CDMA or military communications.

### Summary:
- FSK is the most appropriate choice for data emissions below 30 MHz due to its simplicity and effectiveness in noisy environments. Other options either do not pertain to data modulation or are not commonly used in the specified frequency range. 

### Useful Rule of Thumb:
- For data communications in amateur radio, especially below 30 MHz, remember that FSK is a reliable choice due to its noise resilience and efficiency in bandwidth usage.