Ryan Malloy
0ee7ff0ad7
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
gr-apollo
GNU Radio 3.10+ out-of-tree module for decoding Apollo Unified S-Band (USB) telecommunications signals.
Overview
The Apollo Unified S-Band system was the primary communication link between the spacecraft and Earth during the Apollo missions (1967-1972). This module implements GNU Radio blocks to decode these signals, enabling:
- Reception of Apollo-era recordings
- Integration with the Virtual AGC emulator
- Educational exploration of 1960s space communications
Signal Specifications
| Parameter | Value |
|---|---|
| Downlink Frequency | 2287.5 MHz |
| Uplink Frequency | 2106.40625 MHz |
| Coherent Ratio | 240/221 |
| PM Peak Deviation | 0.133 rad (7.6°) |
| PCM Subcarrier | 1.024 MHz BPSK |
| PCM Bit Rate | 51.2 kbps (high) / 1.6 kbps (low) |
| Voice Subcarrier | 1.25 MHz FM |
| Frame Length | 128 words × 8 bits @ 50 fps |
Installation
# Using uv (recommended)
uv pip install -e .
# Install GRC blocks
cp grc/*.yml ~/.local/share/gnuradio/grc/blocks/
Signal Chain
RF 2287.5 MHz
│
▼
┌─────────────┐
│ Carrier PLL │ ◄── 240/221 coherent recovery
└─────────────┘
│
▼
┌─────────────┐
│ PM Demod │ ◄── 0.133 rad peak deviation
└─────────────┘
│
├────────────────────┬──────────────────┐
▼ ▼ ▼
┌──────────┐ ┌──────────┐ ┌──────────┐
│ 1.024MHz │ │ 1.25 MHz │ │ Ranging │
│ BPSK │ │ FM │ │ PRN │
└──────────┘ └──────────┘ └──────────┘
│ │
▼ ▼
┌──────────┐ ┌──────────┐
│ PCM Sync │ │ Voice │
│ 51.2kbps │ │ 300-3kHz │
└──────────┘ └──────────┘
│
▼
┌──────────┐
│ 128-word │
│ Demux │
└──────────┘
│
▼
Telemetry
References
- Virtual AGC Project
- NASA Technical Reports
- NAA Course A-624: Telecommunication Systems Study Guide (1965)
License
MIT