*Question E2B07:
Which types of modulation are used for amateur television DVB-T signals?*  

*Correct Answer is  B: QAM and QPSK*  

### AI Response: (may contain errors)  

For amateur television DVB-T signals, the correct modulation types are QAM and QPSK. Let's break down why this is the correct answer and why the other choices are incorrect.

### Correct Answer: B: QAM and QPSK

1. **QAM (Quadrature Amplitude Modulation)**:  
   - QAM is a modulation scheme that conveys data by changing the amplitude of two carrier waves. These waves are out of phase with each other by 90 degrees, hence the term "quadrature."
   - It is widely used in digital television broadcasting, including DVB-T, because it efficiently uses bandwidth and can carry a high data rate.

2. **QPSK (Quadrature Phase Shift Keying)**:  
   - QPSK is a type of phase modulation that uses four distinct phase shifts to represent data. It is more bandwidth-efficient than simpler modulation schemes like BPSK (Binary Phase Shift Keying).
   - QPSK is often used in DVB-T for its robustness and efficiency in transmitting digital signals.

### Why the Other Choices are Incorrect:

- **A: FM and FSK**:  
  - **FM (Frequency Modulation)** is not typically used for digital television broadcasting like DVB-T. It is more common in analog TV and radio.
  - **FSK (Frequency Shift Keying)** is a simple digital modulation scheme used for low-speed data transmission, not suitable for the high data rates required by DVB-T.

- **C: AM and OOK**:  
  - **AM (Amplitude Modulation)** is primarily used for analog broadcasting and is not efficient for digital signals like those in DVB-T.
  - **OOK (On-Off Keying)** is a basic form of amplitude modulation used in simple digital communication systems, not suitable for the complex data streams of DVB-T.

- **D: All these choices are correct**:  
  - This is incorrect because not all the modulation types listed are used in DVB-T. Only QAM and QPSK are relevant for DVB-T signals.

### Summary

For DVB-T signals, QAM and QPSK are the appropriate modulation types due to their efficiency and ability to handle high data rates required for digital television broadcasting. Other modulation types like FM, FSK, AM, and OOK are not suitable for this application.