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Fix DSC decoder for ITU-R M.493 compliance

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Correct modulation parameters (1200 bps, 2100/1300 Hz tones), replace
invented format codes with the six ITU-defined specifiers {102, 112,
114, 116, 120, 123}, accept all valid EOS symbols (117, 122, 127),
add parser validation (format, MMSI, raw field, telecommand range),
and fix truthiness bugs that dropped zero-valued fields.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Smittix
2026-02-25 22:02:08 +00:00
parent 935b7a4d9d
commit 8a46293e5c
4 changed files with 339 additions and 88 deletions
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38
utils/dsc/constants.py
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@@ -14,30 +14,26 @@ from __future__ import annotations
# =============================================================================
FORMAT_CODES = {
100: 'DISTRESS', # All ships distress alert
102: 'ALL_SHIPS', # All ships call
104: 'GROUP', # Group call
106: 'DISTRESS_ACK', # Distress acknowledgement
108: 'DISTRESS_RELAY', # Distress relay
110: 'GEOGRAPHIC', # Geographic area call
112: 'INDIVIDUAL', # Individual call
114: 'INDIVIDUAL_ACK', # Individual acknowledgement
116: 'ROUTINE', # Routine call
118: 'SAFETY', # Safety call
120: 'URGENCY', # Urgency call
102: 'ALL_SHIPS', # All ships call
112: 'INDIVIDUAL', # Individual call
114: 'INDIVIDUAL_ACK', # Individual acknowledgement
116: 'GROUP', # Group call (including geographic area)
120: 'DISTRESS', # Distress alert
123: 'ALL_SHIPS_URGENCY_SAFETY', # All ships urgency/safety
}
# Valid ITU-R M.493 format specifiers
VALID_FORMAT_SPECIFIERS = {102, 112, 114, 116, 120, 123}
# Valid EOS (End of Sequence) symbols per ITU-R M.493
VALID_EOS = {117, 122, 127}
# Category priority (lower = higher priority)
CATEGORY_PRIORITY = {
'DISTRESS': 0,
'DISTRESS_ACK': 1,
'DISTRESS_RELAY': 2,
'URGENCY': 3,
'SAFETY': 4,
'ROUTINE': 5,
'ALL_SHIPS_URGENCY_SAFETY': 2,
'ALL_SHIPS': 5,
'GROUP': 5,
'GEOGRAPHIC': 5,
'INDIVIDUAL': 5,
'INDIVIDUAL_ACK': 5,
}
@@ -453,11 +449,11 @@ VHF_CHANNELS = {
# DSC Modulation Parameters
# =============================================================================
DSC_BAUD_RATE = 100 # 100 baud per ITU-R M.493
DSC_BAUD_RATE = 1200 # 1200 bps per ITU-R M.493
# FSK tone frequencies (Hz)
DSC_MARK_FREQ = 1800 # B (mark) - binary 1
DSC_SPACE_FREQ = 1200 # Y (space) - binary 0
# FSK tone frequencies (Hz) on 1700 Hz subcarrier
DSC_MARK_FREQ = 2100 # B (mark) - binary 1
DSC_SPACE_FREQ = 1300 # Y (space) - binary 0
# Audio sample rate for decoding
DSC_AUDIO_SAMPLE_RATE = 48000