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SSTV Transmission Basics
Analog Signal Processing
SSTV uses analog signal processing to transmit images.
Scanning Process
- Image Sampling - Break the image into horizontal lines
- Color Encoding - Use YCbCr color space
- Frequency Modulation - Modulate image data into the audio range
- Transmission - Transmit via RF carrier
Frequency Allocation
Frequency ranges used by SSTV:
- Color Information: 1200-2300 Hz
- Vertical Sync: 1200 Hz (1200ms)
- Horizontal Sync: 1200 Hz (5ms)
- Luminance: 1500-2300 Hz
- Chrominance: Varies by mode
Reception Principles
Synchronization Mechanism
SSTV signals contain sync pulses to help the receiver determine when to start a new line.
- Vertical Sync Pulse - 600 ms, 1200 Hz
- Horizontal Sync Pulse - 5 ms, 1200 Hz
Demodulation Process
- Capture audio signal
- Detect sync pulses
- Measure duration of each frequency
- Convert to pixel values
- Combine into a complete image
Signal-to-Noise Ratio Requirements
Different modes require different SNR:
| Mode | Minimum SNR | Recommended SNR |
|---|---|---|
| M1/M2 | 10 dB | 15 dB |
| P3/P5 | 8 dB | 13 dB |
| Robot 36 | 12 dB | 18 dB |
Interference Factors
Factors affecting SSTV reception:
- Multipath propagation
- Frequency drift
- Clock errors
- Audio distortion
- Environmental noise
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