Question
What signals SSTV receiving software to begin a new picture line?
Answer Options
- A) Specific tone frequencies
- B) Elapsed time
- C) Specific tone amplitudes
- D) A two-tone signal
Correct Answer: A
Explanation
In analog Slow-Scan Television (SSTV), the synchronization of the image display is achieved using specific, standardized audio tones. The receiver must know exactly when one line ends and the next begins to properly construct the image, especially since the tone itself carries the brightness information.
To signal the start of a new line, the SSTV receiver software looks for specific tone frequencies that act as horizontal synchronization pulses. The international SSTV standard uses a tone of 1,200 Hz for a duration of 5 milliseconds (ms) as the signal for the start of a new picture line (horizontal synchronization pulse). This precise, standardized frequency triggers the receiver to reset its horizontal scanning sequence.
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