*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 analog slow-scan television (SSTV), the brightness of the picture is encoded by the tone frequency. Here's why:

1. **Correct Answer: Tone frequency**  
   - In SSTV, different frequencies represent different brightness levels. Higher frequencies correspond to brighter parts of the image, while lower frequencies correspond to darker parts. This method of encoding allows the receiver to interpret the varying frequencies as varying brightness levels in the image.

2. **Why the other choices are incorrect:**
   - **Tone amplitude**: This would imply that the loudness or strength of the tone encodes brightness, which is not the case in SSTV. Amplitude is not used for encoding brightness; it is typically used for other purposes, such as signal strength.
   - **Sync amplitude**: Sync signals are used to synchronize the start of each line or frame in the image, not to encode brightness. The amplitude of these sync signals is not related to the brightness of the picture.
   - **Sync frequency**: Similar to sync amplitude, sync frequency is related to timing and synchronization, not to the encoding of brightness. Sync signals ensure that the image is displayed correctly, but they do not carry brightness information.

In summary, the brightness in an analog SSTV signal is encoded by the frequency of the tone, making "Tone frequency" the correct answer.