*Question T8A04:
Which type of modulation is commonly used for VHF and UHF voice repeaters?*  

*Correct Answer is  D: FM or PM*  

### AI Response: (may contain errors)  

To understand which type of modulation is commonly used for VHF and UHF voice repeaters, let's break down the options:

### Correct Answer: D: FM or PM

- **Frequency Modulation (FM)** is the most widely used modulation method for VHF and UHF voice communications, especially in amateur radio repeaters. 
- **Phase Modulation (PM)** is closely related to FM and can also be used, but FM is the predominant method.

**Why FM is used:**
- FM provides better noise immunity compared to AM, making it ideal for voice communications in the VHF and UHF bands.
- It allows for clearer audio quality and is less susceptible to interference.

### Why the Other Choices are Incorrect:

- **A: AM (Amplitude Modulation)**
  - AM is less efficient in terms of bandwidth and power usage compared to FM. It is more susceptible to noise and interference, which makes it less suitable for VHF and UHF voice communications.

- **B: SSB (Single Sideband)**
  - SSB is a form of amplitude modulation that is more efficient than standard AM, but it is primarily used for long-distance communication and not typically for local voice repeaters. It requires more complex equipment and is not as user-friendly for casual operators.

- **C: PSK (Phase Shift Keying)**
  - PSK is a digital modulation technique used for data transmission rather than voice communications. It is not suitable for voice repeaters, which require analog modulation methods like FM.

### Summary

For VHF and UHF voice repeaters, FM is the preferred modulation method due to its robustness against noise and better audio quality. Other methods like AM, SSB, and PSK are either less efficient or not designed for voice communication in this context.