Ryan Malloy 0ee7ff0ad7 Implement full Apollo USB downlink decoder chain ...

Complete signal processing pipeline from complex baseband to decoded
PCM telemetry, verified against the 1965 NAA Study Guide (A-624):

Core demod (Phase 1):
  - PM demodulator with carrier PLL recovery
  - 1.024 MHz subcarrier extractor (bandpass + downconvert)
  - BPSK demodulator with Costas loop + symbol sync
  - Convenience hier_block2 combining subcarrier + BPSK

PCM frame processing (Phase 2):
  - 32-bit frame sync with Hamming distance correlator
  - SEARCH/VERIFY/LOCKED state machine, complement-on-odd handling
  - Frame demultiplexer (128-word, A/D voltage scaling)
  - AGC downlink decoder (15-bit word reassembly from DNTM1/DNTM2)

Voice and analog (Phase 3):
  - 1.25 MHz FM voice subcarrier demod to 8 kHz audio
  - SCO demodulator for 9 analog sensor channels (14.5-165 kHz)

Virtual AGC integration (Phase 4):
  - TCP bridge client with auto-reconnect and channel filtering
  - DSKY uplink encoder (VERB/NOUN/DATA command sequences)

Top-level receiver (Phase 5):
  - usb_downlink_receiver hier_block2: one block, complex in, PDUs out
  - 14 GRC block YAML definitions for GNU Radio Companion
  - Example scripts for signal analysis and full-chain demo

Infrastructure:
  - constants.py with all timing/frequency/frame parameters
  - protocol.py for sync word + AGC packet encode/decode
  - Synthetic USB signal generator for testing
  - 222 tests passing, ruff lint clean

2026-02-20 13:18:42 -07:00

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