*Question E2B12:
What signals SSTV receiving software to begin a new picture line?*  

*Correct Answer is  A: Specific tone frequencies*  

### AI Response: (may contain errors)  

To understand how SSTV (Slow Scan Television) receiving software knows when to begin a new picture line, let's break down the correct answer and the other options.

### Correct Answer: A - Specific tone frequencies

- **Explanation**: SSTV signals use specific audio tone frequencies to encode the image data. The receiving software listens for these tones to determine when to start a new line of the picture. Each line of the image is transmitted as a series of tones, and the software is programmed to recognize the frequency patterns that indicate the start of a new line.

### Why the Other Choices are Incorrect:

- **B: Elapsed time**: 
  - While timing is important in SSTV, the software does not rely solely on elapsed time to determine when to start a new line. The timing can vary based on the transmission speed and other factors, making it unreliable for line detection.

- **C: Specific tone amplitudes**: 
  - Amplitude refers to the strength of the signal, but SSTV relies on frequency modulation rather than amplitude modulation for line detection. The software does not use amplitude levels to signal the start of a new line.

- **D: A two-tone signal**: 
  - While SSTV may use multiple tones, it does not specifically use a two-tone signal to indicate the start of a new line. The software is designed to recognize specific frequency patterns rather than just two tones.

### Summary

In SSTV, the key to starting a new picture line lies in recognizing specific tone frequencies. This allows the receiving software to accurately decode the transmitted image data. Understanding the role of frequency in SSTV is crucial for the Extra Class exam.