# 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](https://www.ibiblio.org/apollo/) 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

```bash
# 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](https://www.ibiblio.org/apollo/)
- [NASA Technical Reports](https://ntrs.nasa.gov/)
- NAA Course A-624: Telecommunication Systems Study Guide (1965)

## License

MIT