Project Abstract

A TNC (Terminal Node Controller) is a device that was developed for the ham radio community to allow communications over packet radio networks. These devices usually contain a modem and interface to a radio as well as a serial port that connects to a dumb terminal, or currently a computer running a terminal program, along with a CPU, Ram memory occasionally backed up by a battery, and a Rom device that held the non volatile programming for the device. In essence the tnc is a complete microcomputer systems designed to run stand alone when not connected to a terminal or computer. Most of the basic designs were based on the Z80 Microprocessor and followed the basic design of the tnc2 published by TAPR (Tucson Amateur Packet Radio) which is beyond the scope of this document. For a more complete read of Packet Radio please visit Introduction to Packet Radio by Larry Kenney, WB9LOZ.

Most Amateur Radio Operators nowadays wanting to work in Packet Radio use software that has been developed for the PC which contains a software modem and terminal program to connect to the packet radio network. One such software is UZ7HO software Packet-Radio TNC. However this requires the PC to always be operational in order to stay connected to the packet network 24x7. Even though there are still TNC devices being produced by companies such as Kantronics, these devices usually come at a high cost, and even devices that are old circa 1980's that are sold on Ebay are usually expensive and due to age many have issues and don't work.

With the advent of emulation technologies for PC's a thought popped into my head, why not emulate the hardware of a TNC device on a PC running the linux operating system of which there are many embedded versions, allowing emulation not only on a standard PC but very powerful and inexpensive devices such as the Raspberry Pi! Since I myself had an old TNC, specifically a Heathkit HK21 Pocket Packet, the hardware of which was designed in Japan and also followed some other designs by AOR, Inc. (AR-210) as well as Paccomm, Inc., I decided to attempt to emulate this device and a project was born.