Charles Brain Modem Core - Headless TCP Server

Wrapper for the original m188110a MIL-STD-188-110A modem core by Charles Brain (G4GUO).

Stripped of Qt/GUI dependencies for headless testing via TCP/IP and PCM files.

Quick Start

A pre-built Windows executable is included in the repository:

.\brain_modem_server.exe

Server listens on:

• Control: localhost:3999
• Data: localhost:3998

Features

• TCP Control Port (3999): ASCII commands for modem control
• TCP Data Port (3998): Binary data TX/RX
• PCM File Output: TX audio saved to files for analysis
• PCM File Inject: Feed RX audio from files for testing
• No Audio Devices: Pure file-based operation for automated testing

Commands (via Control Port)

Command	Description
CMD:DATA RATE:<mode>	Set mode (e.g., "600S", "1200L", "2400S")
CMD:SENDBUFFER	Transmit buffered data
CMD:RESET MDM	Reset modem state
CMD:KILL TX	Abort transmission
CMD:RECORD TX:ON/OFF	Enable/disable PCM recording
CMD:RECORD PREFIX:<name>	Set PCM filename prefix
CMD:RXAUDIOINJECT:<path>	Inject PCM file to RX
CMD:QUERY:STATUS	Get modem status
CMD:QUERY:MODES	List supported modes
CMD:QUERY:VERSION	Get version string

Supported Modes

• 75S, 75L (75 bps)
• 150S, 150L (150 bps)
• 300S, 300L (300 bps)
• 600S, 600L (600 bps)
• 1200S, 1200L (1200 bps)
• 2400S, 2400L (2400 bps)

(S = Short interleave, L = Long interleave)

Testing Workflow

1. Start server
2. Connect control client to port 3999
3. Send data to port 3998
4. Send CMD:DATA RATE:600S
5. Send CMD:SENDBUFFER
6. PCM file appears in ./tx_pcm_out/
7. Use CMD:RXAUDIOINJECT:<pcm_file> to test decode
8. Decoded data appears on port 3998

Comparison Testing

This wrapper enables fair comparison between:

• Charles Brain modem core (this project)
• Phoenix Nest modem core

Both use identical:

• TCP interface (ports 3998/3999)
• Command set
• PCM file format (48kHz 16-bit)

Credits

• Original modem core: Charles Brain (G4GUO) (m188110a)
• TCP wrapper: Phoenix Nest LLC
• MIL-STD-188-110A specification: U.S. Department of Defense

License

The modem core is distributed as a pre-compiled static library. Source code is not included. Wrapper code (src/*) is proprietary, Copyright (C) 2025 Phoenix Nest LLC.