*Question E2B10:
What aspect of an analog slow-scan television signal encodes the brightness of the picture?*  

*Correct Answer is  A: Tone frequency*  

### AI Response: (may contain errors)  

In an analog slow-scan television (SSTV) signal, the brightness of the picture is encoded in the tone frequency. Here's a breakdown of why this is the case and why the other options are incorrect:

### Correct Answer: Tone Frequency
- **Explanation**: In SSTV, the brightness of the image is represented by different frequencies of audio tones. Higher frequencies correspond to brighter areas of the image, while lower frequencies correspond to darker areas. This modulation allows the visual information to be transmitted over radio waves effectively.

### Why the Other Choices are Incorrect:
- **A: Tone Frequency**: This is the correct answer, as explained above.
  
- **B: Tone Amplitude**: The amplitude of the tone in SSTV primarily affects the contrast of the image rather than the brightness. While a higher amplitude can make the signal stronger, it does not directly encode the brightness levels of the picture.

- **C: Sync Amplitude**: The sync amplitude is related to the synchronization pulses that help the receiver align the incoming signal. It does not carry information about the brightness of the image.

- **D: Sync Frequency**: The sync frequency is used to establish the timing of the video signal but does not encode brightness information. It ensures that the receiver can properly decode the image but does not affect the brightness levels.

### Summary
- Brightness in SSTV is encoded in tone frequency.
- Tone amplitude affects contrast, while sync amplitude and frequency are related to timing and synchronization, not brightness.

This understanding is crucial for interpreting SSTV signals and preparing for the Extra Class exam.