Audiocat is a command-line utility for Linux that reads and writes encrypted data across peer-to-peer or broadcast audio connections, using minimodem and gpg.

It is a powerful tool that can be combined with any audio infrastructure (like PSTN, cellular network, internet, radio, walkie-talkies) to provide a secure communication channel through an audio tunnel.

The audio interfaces behave like data-diodes, each allowing unidirectional data transmission only, thus preventing data-leaks and malware-injection.

This enables an "enhanced"-end-to-end encryption (E-E2EE) which notably increases security and privacy, especially when the end devices are completely offline (air-gapped-system), thus providing an effective barrier against "legal or illegal" client-side-scanning!

Simple minimodem BBS with a 3d printed acoustic coupler case. The acoustic coupler was designed to hold a USB speaker and microphone, which you can buy from Adafruit.

Requires Linux. PJSUA and minimodem must be installed. The BBS uses shell scripts and javascript to relay messages via minimodem over VoIP. On the server side, start PJSUA then start the phoneMonitor.sh script. Minimodem is set to run at 100bps. Edit the shell scripts if you want to change the baud. You will need to edit the clientSide.sh script, minimodem -A alsa option should match your USB microphone and speaker. Use arecord -l and aplay -l linux commands to find their card numbers.

Dire Wolf is a software "soundcard" AX.25 packet modem/TNC and APRS encoder/decoder. It can be used stand-alone to observe APRS traffic, as a tracker, digipeater, APRStt gateway, or Internet Gateway (IGate).

In the early days of Amateur Packet Radio, it was necessary to use an expensive "Terminal Node Controller" (TNC) with specialized hardware. You can now get better results at lower cost by connecting your radio to the sound card of a computer and using software to decode the signals.

A simple v.23 modem including the data link layer. This is an application for Asterisk. Place a call over SIP and it'll connect via Telnet to a pre-configured service in the dialplan.

V.23 Softmodem for Asterisk with some Bildschirmtext-specific stuff in it. Pretends to be a modem but it actually sets up a telnet-like TCP session to an IP address. Like many things with Asterisk, you have to compile everything from source with this module in a particular location.

minimodem is a command-line utility which implements a virtual FSK (forward shift keying) modem. Hook it into an audio source and it will act just like a modem, sending and receiving data transmissions. Can also interpret recordings of transmissions and generate new ones from traffic you send it. Who needs a serial modem when you've got this? Includes support for various standard FSK protocols such as Bell103, Bell202, RTTY, TTY/TDD, NOAA SAME, and Caller-ID.

Maybe I can use this to write my VoIP wardialer?