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https://github.com/smittix/intercept.git
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ef7d8cca9f
slowrx is a GTK GUI app that doesn't support CLI usage, so the SSTV decoder was silently failing. This replaces it with a pure Python implementation using numpy and Pillow that supports Robot36/72, Martin1/2, Scottie1/2, and PD120/180 modes via VIS header auto-detection. Key implementation details: - Generalized Goertzel (DTFT) for exact-frequency tone detection - Vectorized batch Goertzel for real-time pixel decoding performance - Overlapping analysis windows for short-window frequency estimation - VIS header detection state machine with parity validation - Per-line sync re-synchronization for drift tolerance Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
93 lines
3.1 KiB
Python
93 lines
3.1 KiB
Python
"""SSTV protocol constants.
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VIS (Vertical Interval Signaling) codes, frequency assignments, and timing
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constants for all supported SSTV modes per the SSTV protocol specification.
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"""
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from __future__ import annotations
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# ---------------------------------------------------------------------------
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# Audio / DSP
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# ---------------------------------------------------------------------------
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SAMPLE_RATE = 48000 # Hz - standard audio sample rate used by rtl_fm
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# Window size for Goertzel tone detection (5 ms at 48 kHz = 240 samples)
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GOERTZEL_WINDOW = 240
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# Chunk size for reading from rtl_fm (100 ms = 4800 samples)
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STREAM_CHUNK_SAMPLES = 4800
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# ---------------------------------------------------------------------------
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# SSTV tone frequencies (Hz)
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# ---------------------------------------------------------------------------
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FREQ_VIS_BIT_1 = 1100 # VIS logic 1
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FREQ_SYNC = 1200 # Horizontal sync pulse
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FREQ_VIS_BIT_0 = 1300 # VIS logic 0
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FREQ_BREAK = 1200 # Break tone in VIS header (same as sync)
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FREQ_LEADER = 1900 # Leader / calibration tone
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FREQ_BLACK = 1500 # Black level
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FREQ_WHITE = 2300 # White level
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# Pixel luminance mapping range
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FREQ_PIXEL_LOW = 1500 # 0 luminance
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FREQ_PIXEL_HIGH = 2300 # 255 luminance
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# Frequency tolerance for tone detection (Hz)
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FREQ_TOLERANCE = 50
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# ---------------------------------------------------------------------------
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# VIS header timing (seconds)
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# ---------------------------------------------------------------------------
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VIS_LEADER_MIN = 0.200 # Minimum leader tone duration
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VIS_LEADER_MAX = 0.500 # Maximum leader tone duration
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VIS_LEADER_NOMINAL = 0.300 # Nominal leader tone duration
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VIS_BREAK_DURATION = 0.010 # Break pulse duration (10 ms)
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VIS_BIT_DURATION = 0.030 # Each VIS data bit (30 ms)
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VIS_START_BIT_DURATION = 0.030 # Start bit (30 ms)
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VIS_STOP_BIT_DURATION = 0.030 # Stop bit (30 ms)
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# Timing tolerance for VIS detection
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VIS_TIMING_TOLERANCE = 0.5 # 50% tolerance on durations
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# ---------------------------------------------------------------------------
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# VIS code → mode name mapping
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# ---------------------------------------------------------------------------
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VIS_CODES: dict[int, str] = {
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8: 'Robot36',
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12: 'Robot72',
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44: 'Martin1',
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40: 'Martin2',
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60: 'Scottie1',
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56: 'Scottie2',
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93: 'PD120',
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95: 'PD180',
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# Less common but recognized
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4: 'Robot24',
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36: 'Martin3',
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52: 'Scottie3',
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55: 'ScottieDX',
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113: 'PD240',
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96: 'PD90',
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98: 'PD160',
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}
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# Reverse mapping: mode name → VIS code
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MODE_TO_VIS: dict[str, int] = {v: k for k, v in VIS_CODES.items()}
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# ---------------------------------------------------------------------------
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# Common SSTV modes list (for UI / status)
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# ---------------------------------------------------------------------------
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SSTV_MODES = [
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'PD120', 'PD180', 'Martin1', 'Martin2',
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'Scottie1', 'Scottie2', 'Robot36', 'Robot72',
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]
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# ISS SSTV frequency
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ISS_SSTV_FREQ = 145.800 # MHz
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# Speed of light in m/s
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SPEED_OF_LIGHT = 299_792_458
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# Minimum energy ratio for valid tone detection (vs noise floor)
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MIN_ENERGY_RATIO = 5.0
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