This library allows you to communicate small amounts of data between air-gapped devices using sound. It implements a simple FSK-based transmission protocol that can be easily integrated in various projects. The bandwidth rate is between 8-16 bytes/sec depending on the protocol parameters. Error correction codes (ECC) are used to improve demodulation robustness.

This library is used only to generate and analyze the RAW waveforms that are played and captured from your audio devices (speakers, microphones, etc.). You are free to use any audio backend (e.g. PulseAudio, ALSA, etc.) as long as you provide callbacks for queuing and dequeuing audio samples.

It's designed for devices that are relatively close to one another that need to exchange information, like a PC and a phone or a con badge and a door lock. It even links to some mobile apps that can be used for proof-of-concept testing (but they're kind of old so they might not be installable for you).

At its core, CATS is a packet radio standard primarily designed for autonomous position reports, but is versatile enough to support a much wider scope of communication. CATS packets are extremely versatile, consisting of multiple "Whiskers" which make up the packet. Whiskers come in several types. For example, a typical CATS position beacon would likely contain an Identification Whisker, GPS Whisker, and potentially a Comment Whisker and Timestamp Whisker. Different Whiskers can be mixed and matched to allow a wide range of data to be encoded. Detailed information on CATS can be found in the standard, linked below.

CATS is ultimately meant to be a replacement to APRS. Although APRS was magnificent when it was first developed, current technology allows us to do better. APRS also suffers from decades of bloat, making the standard difficult to learn.

Minimal dumb-terminal emulation program. Good for interacting with microcontrollers and occasionally routers.

PSKmail is a software-based narrowband communications package for amateur radio datacomm. It uses multiple PSK modes to achieve different speeds. The client runs on Windows, Linux, and MacOSX. The server is written in Perl. Allows you to send and receive mail, pull text off the Web, send and receive APRS traffic, and chat between clients.