 What is zFM?

zFM is a small, self-hosted “push-to-talk style” voice system. Users connect to a single server (TCP), join a talkgroup, and transmit audio either by pressing-to-talk or using VOX (voice-activated transmit). The server keeps track of who is currently speaking per talkgroup, routes audio to listeners, and exposes a live dashboard in the browser.

 What’s possible with zFM?

Here is what zFM can do today, based on the current codebase:

• Talkgroups (public/hidden/admin-only visibility in the dashboard)
• Single active speaker per talkgroup with time-limit protection (max_talk_ms)
• VOX mode (hands-free transmit) or classic push-to-talk
• Hardware PTT options (GPIO / CM108 style control if available, serial RTS/DTR, and command hooks)
• Web dashboard: active speaker, talkgroup list, bridged TG graph, connected users, audio level + spectrum/waterfall view
• Admin UI in the browser: manage users, talkgroups, bridges, peers, time/weather settings
• Admin commands from the console client: kick/mute/ban, list users, last-heard, etc.
• Bridge peers: connect multiple servers together using rule-based talkgroup forwarding
• Optional announcements (time + katwarn + weather) mixed into a talkgroup, when enabled
• Optional ADPCM (bandwidth saver) with jitter buffering and PLC options
• RX / TX squelch options (auto / level / hang time) to suppress noise

 Quick start (recommended workflow)

This is the shortest path to “I can talk and I can see the dashboard”.

# Linux
./zfm_server

# Windows (PowerShell)
.\zfm_server.exe
								

http://<server-ip>:8080/
								

http://<server-ip>:8080/admin.html
								

# Uses client.json
./zfm_client
							

 Software

Choose the version of the software that matches your platform.

 Screenshot

Reference screenshots related to configuration, layout, or issues.

Server / Client

Web Dashboard / Admin Control

Client GUI

 Install / Build on Linux

zFM is plain C++ and does not require heavy frameworks. You mainly need a compiler, PortAudio for the console client, and optionally OpenSSL + SDL2 (for HTTPS / GUI).

# Debian/Ubuntu
sudo apt update
sudo apt install -y build-essential portaudio19-dev libssl-dev

# Optional GUI client
sudo apt install -y libsdl2-dev libsdl2-ttf-dev
								

# Server (HTTP dashboard)
g++ -O2 -std=c++17 -pthread server.cpp -o zfm_server

# Server with HTTPS (requires OpenSSL, compile with USE_OPENSSL=1)
g++ -O2 -std=c++17 -pthread -DUSE_OPENSSL=1 server.cpp -lssl -lcrypto -o zfm_server

# Console client (PortAudio)
g++ -O2 -std=c++17 -pthread client.cpp -lportaudio -o zfm_client
							

 Install / Build on Windows

On Windows, the server and client use Winsock. You can build using Visual Studio (MSVC) or MinGW-w64. The only “external” dependency you typically need is PortAudio for the client (and OpenSSL if you want HTTPS).

:: Server
g++ -O2 -std=c++17 server.cpp -lws2_32 -o zfm_server.exe

:: Client (needs PortAudio)
g++ -O2 -std=c++17 client.cpp -lws2_32 -lportaudio -o zfm_client.exe
								

 Optional GUI client (SDL2)

The GUI wrapper (client_gui.cpp) includes the console client code and adds a windowed UI using SDL2 and SDL2_ttf. This is optional - the console client already supports all core features.

g++ -O2 -std=c++17 -pthread -DGUI client_gui.cpp -lportaudio -lSDL2 -lSDL2_ttf -o zfm_client_gui
							

 Web dashboard

The server hosts a live dashboard (HTML/CSS/JS) from http_root (default: dashboard). It periodically queries server status and renders:

• Server time, katwarn and weather (if enabled)
• Number of connected clients
• Now speaking (active speaker)
• Talkgroups: speaker, duration, listeners, audio level, activity “heat”
• Talkgroup links (bridges) and peer connection state
• Connected users list
• Spectrum / waterfall focused on a talkgroup (click a TG row to focus; optional auto-follow)

 Admin panel (web)

Open /admin.html in your browser and sign in with a user that has OPERATOR or ADMIN role. The panel is built for touch/mobile too (drawer menu, modal editors).

 Client commands (console)

When VOX is disabled, the console client waits for short commands:

 Admin commands (from the client)

In the console client you can send admin commands by typing /command …. The client will send ADMIN messages to the server.

 server.json (server configuration)

The server loads server.json at startup and rewrites it when you change settings in the admin panel (or via admin commands). Below is an example layout with notes.

{
  "server_name": "Server",
  "peer_secret": "password",
  "server_port": 26613,
  "max_talk_ms": 600000,
  "http_root": "dashboard",
  "http_port": 8080,
  "https_port": 8443,
  "https_cert_file": "cert.pem",
  "https_key_file": "key.pem",
  "time_announcement": {
    "enabled": true,
    "folder": "audio",
    "volume_factor": 0.35
  },
  "weather_enabled": false,
  "weather_host_ip": "api.openweathermap.org",
  "weather_talkgroup": "Weather",
  "weather_interval_sec": 600,
  "weather_api_key": "api_key",
  "weather_lat": "50.1109",
  "weather_lon": "8.6821",
  "weather_city_key": "Frankfurt",
  "katwarn_enabled": false,
  "katwarn_host": "nina.api.proxy.bund.dev",
  "katwarn_talkgroup": "KATWARN",
  "katwarn_interval_sec": 3600,
  "katwarn_ars": "064120000000",
  "katwarn_city_key": "katwarn_frankfurt",
  "users": [
    {
      "callsign": "Admin",
      "password": "password",
      "role": "admin",
      "banned": false,
      "priority": 100,
      "talkgroups": ["Gateway","Public","Weather","Operation","Admin"]
    },
    {
      "callsign": "Operator",
      "password": "password",
      "role": "operator",
      "banned": false,
      "priority": 50,
      "talkgroups": ["Gateway","Public","Weather","Operation"]
    },
    {
      "callsign": "Guest",
      "password": "password",
      "role": "user",
      "banned": false,
      "priority": 0,
      "talkgroups": ["Gateway","Public"]
    }
  ],
  "talkgroups": [
    { "name": "Gateway", "mode": "public" },
    { "name": "Public", "mode": "public" },
    { "name": "Weather", "mode": "public" },
    { "name": "Operation", "mode": "hide" },
    { "name": "Admin", "mode": "admin" }
  ],
  "bridges": {
    "Weather": ["Gateway","Public"],
    "Gateway": ["Public"],
    "Public": ["Gateway"]
  },
  "peers": [
    {
      "name": "Remote Server",
      "host": "127.0.0.1",
      "port": 26613,
      "secret": "premote_password",
      "rules": ["Gateway=Gateway:both", "Public=Public:both"]
    }
  ]
}
						

 client.json (client configuration)

The console client reads client.json and uses it to pick the server, audio devices, talkgroup, VOX/PTT behavior, and audio processing options.

{
  "mode": "Server",
  "server_ip": "127.0.0.1",
  "server_port": 26613,
  "callsign": "Guest",
  "password": "password",
  "talkgroup": "Gateway",
  "sample_rate": 22050,
  "frames_per_buffer": 960,
  "channels": 1,
  "input_device_index": 0,
  "output_device_index": 0,
  "gpio_ptt_enabled": false,
  "gpio_ptt_pin": 18,
  "gpio_ptt_active_high": true,
  "gpio_ptt_hold_ms": 250,
  "keyboard_ptt_enabled": true,
  "keyboard_ptt_keycode": 32,
  "vox_enabled": false,
  "vox_threshold": 5000,
  "input_gain": 100,
  "output_gain": 100,
  "ptt_cmd_on": "",
  "ptt_cmd_off": "",
  "ptt_serial_port": "",
  "ptt_serial_line": "RTS",
  "ptt_serial_invert": false,
  "roger_sound": 1,
  "use_adpcm": false,
  "adpcm_adaptive": true,
  "adpcm_jitter_frames": 3,
  "adpcm_plc_ms": 120,
  "rx_squelch_enabled": false,
  "rx_squelch_auto": true,
  "rx_squelch_level": 55,
  "rx_squelch_voice_pct": 55,
  "rx_squelch_hang_ms": 450,
  "tx_squelch_enabled": false,
  "tx_squelch_auto": true,
  "tx_squelch_level": 55,
  "tx_squelch_voice_pct": 55,
  "tx_squelch_hang_ms": 450
}
						

 License

This software is experimental and provided "AS IS". Use at your own risk.

MIT License

Copyright (c) 2025 zFM

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHOR OR COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
						

 Katwarn Info

Below is a complete list of all 16 German federal states with their capital city, latitude/longitude, and the corresponding "ARC" for Katwarn.

 Troubleshooting

 Security & best practices

• Use strong passwords for operator/admin accounts.
• Don’t expose admin endpoints publicly without protection (VPN / reverse proxy auth).
• Keep backups of server.json before large changes.
• Use HTTPS (or a reverse proxy) if you access the dashboard over the internet.
• Prefer running the server under a dedicated user account with limited permissions.

 FAQ

sudo tee /etc/udev/rules.d/99-cm108-ptt.rules >/dev/null <<'RULE'
SUBSYSTEM=="hidraw", ATTRS{idVendor}=="0d8c", ATTRS{idProduct}=="013c", MODE="0660", GROUP="plugdev"
RULE

sudo usermod -aG plugdev "$USER"
sudo udevadm control --reload-rules
sudo udevadm trigger
								

sudo systemctl stop hciuart
sudo systemctl disable hciuart

sudo tee /etc/udev/rules.d/90-cm108.rules >/dev/null <<'RULE'
# block pulseaudio using the soundcard for SVXLINK
ATTRS{idVendor}=="0d8c", ENV{PULSE_IGNORE}="1"
# create a symlink /dev/hidrawX to /dev/cm108gpio
SUBSYSTEM=="hidraw", ATTRS{idVendor}=="0d8c", SYMLINK+="cm108gpio", MODE="0666"
RULE

sudo usermod -aG audio $USER
sudo usermod -aG plugdev "$USER"
sudo udevadm control --reload-rules
sudo udevadm trigger