*Question T8A12:
Which of the following is a disadvantage of FM compared with single sideband?*  

*Correct Answer is  B: Only one signal can be received at a time*  

### AI Response: (may contain errors)  

The correct answer to the question is **B: Only one signal can be received at a time**. Let's break down why this is the case and why the other options are incorrect.

### Explanation of the Correct Answer (B)
- **Only one signal can be received at a time**: 
  - FM (Frequency Modulation) signals occupy a wider bandwidth compared to SSB (Single Sideband) signals. This means that when using FM, the receiver is typically tuned to a specific frequency and can only demodulate one signal at that frequency. In contrast, SSB can allow for better selectivity, enabling the reception of multiple signals in a narrower bandwidth.

### Explanation of the Incorrect Answers
- **A: Voice quality is poorer**: 
  - This statement is incorrect because FM generally provides better voice quality than SSB due to its higher fidelity and resistance to noise. FM is less susceptible to amplitude variations, which can degrade audio quality, making it preferable for voice communications.

- **C: FM signals are harder to tune**: 
  - This is also incorrect. While FM receivers may require more precise tuning due to their wider bandwidth, they are not inherently harder to tune than SSB receivers. In fact, many FM receivers are designed to be user-friendly and can automatically adjust to the signal.

- **D: All these choices are correct**: 
  - Since options A and C are incorrect, this choice cannot be correct either. 

### Summary
- FM provides better voice quality and is not necessarily harder to tune compared to SSB. The main disadvantage of FM is its wider bandwidth, which limits the ability to receive multiple signals simultaneously.

### Useful Rule of Thumb
- **Bandwidth Consideration**: 
  - FM typically requires a bandwidth of about $15 \, kHz$ for standard voice communications, while SSB can operate within a bandwidth of about $2.7 \, kHz$. This difference is crucial when considering the number of signals that can be received in a given frequency range.