A terminal node controller (TNC) is a device used by

amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency radio spectrum, spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emer ...

operators to participate in AX.25

packet radio In digital radio, packet radio is the application of packet switching techniques to digital radio communications. Packet radio uses a packet switching Communication protocol, protocol as opposed to circuit switching or message switching protocols ...

networks. It is similar in function to the Packet Assembler/Disassemblers used on

X.25 X.25 is an ITU-T standard protocol suite for Packet switched network, packet-switched data communication in wide area network, wide area networks (WAN). It was originally defined by the CCITT, International Telegraph and Telephone Consultative Co ...

networks, with the addition of a modem to convert baseband digital signals to audio tones. The first TNC, the VADCG board, was originally developed by Doug Lockhart, VE7APU, of

Vancouver Vancouver is a major city in Western Canada, located in the Lower Mainland region of British Columbia. As the List of cities in British Columbia, most populous city in the province, the 2021 Canadian census recorded 662,248 people in the cit ...

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

. Amateur Radio TNCs were first developed in 1978 in Canada by the Montreal Amateur Radio Club and the Vancouver Area Digital Communications group. These never gained much popularity because only a bare

printed circuit board A printed circuit board (PCB), also called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...

was made available and builders had to gather up a large number of components. In 1983, the Tucson Amateur Packet Radio (TAPR) association produced complete kits for their TNC-1 design. This was later available as the

Heathkit Heathkit is the brand name of kits and other electronic products produced and marketed by the Heath Company. The products over the decades have included electronic test equipment, high fidelity home audio equipment, television receivers, amateu ...

HD-4040. A few years later, the improved TNC-2 became available, and it was licensed to commercial manufacturers such as MFJ. In 1986, the improved "TNC+" was designed to run programs and protocols developed for the original TNC board. TNC+ also included an assembler and a version of Forth ( STOIC), which runs on the TNC+ itself, to support developing new programs and protocols. In 2018 Nino Carillo (KK4HEJ) developed and produced a TNC (the ''NinoTNC'') with (currently) 16 different data modes, from 300 baud AFSK to 19,200 C4FSK.It has a KISS interface to the compute device, and implements IL2P (Improved Layer 2 Protocol) for Forward Error Correction (FEC) in some modes.

Description

Terminal-Node-Controller-Kantronics-9612plus-0a

A typical model consists of a

microprocessor A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...

, a

modem The Democratic Movement (, ; MoDem ) is a centre to centre-right political party in France, whose main ideological trends are liberalism and Christian democracy, and that is characterised by a strong pro-Europeanist stance. MoDem was establis ...

, and

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

(in

EPROM An EPROM (rarely EROM), or erasable programmable read-only memory, is a type of programmable read-only memory (PROM) integrated circuit, chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored d ...

) that implements the AX.25 protocol and provides a

command line interface A command-line interface (CLI) is a means of interacting with software via commands each formatted as a line of text. Command-line interfaces emerged in the mid-1960s, on computer terminals, as an interactive and more user-friendly alternati ...

to the user. (Commonly, this software provides other functionality as well, such as a basic

bulletin board system A bulletin board system (BBS), also called a computer bulletin board service (CBBS), is a computer server running list of BBS software, software that allows users to connect to the system using a terminal program. Once logged in, the user perfor ...

to receive messages while the operator is away.) Because the TNC contains all the intelligence needed to communicate over an AX.25 network, no external

computer A computer is a machine that can be Computer programming, programmed to automatically Execution (computing), carry out sequences of arithmetic or logical operations (''computation''). Modern digital electronic computers can perform generic set ...

is required. All of the network's resources can be accessed using a

dumb terminal A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. Most early computers only had a front panel to input or display ...

. The TNC connects to the terminal and a radio

transceiver In radio communication, a transceiver is an electronic device which is a combination of a radio ''trans''mitter and a re''ceiver'', hence the name. It can both transmit and receive radio waves using an antenna, for communication purposes. The ...

. Data from the terminal is formatted into AX.25 packets and

modulated Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message ...

into audio signals (in traditional applications) for transmission by the radio. Received signals are demodulated, the data unformatted, and the output sent to the terminal for display. In addition to these functions, the TNC manages the radio channel according to guidelines in the AX.25 specification. Early usage was mostly one-to-one communication, either between two people or a person to an automated Bulletin Board or E-mail system.

Current status

Since the late 1990s, most AX.25 usage has shifted to a different one-to-many communication paradigm with the Automatic Packet Reporting System (APRS). The TNCs of the 1980s and 1990s were complete solutions that only needed a radio and an optional

. As home computers made their way into

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"shacks," there was a movement toward simpler, cheaper "KISS" (Keep It Simple, Stupid) devices. These have a modem and minimal processing of the AX.25 protocol. Most of the processing is moved to the personal computer. The next logical step in the evolution is to eliminate the specialized hardware and move all of the processing to a computer. A " soundcard" is used for audio to and from the radio. Everything else is done in software. Some of the earlier attempts performed poorly, giving this approach a bad reputation. Modern software TNCs, using digital signal processing (DSP) techniques, can successfully decode poor quality signals that the older equipment can't. Some handheld and mobile VHF radios currently on the market incorporate TNC abilities within the radio itself in support of the APRS protocol. Many TNCs are still in use, especially in unattended stations where reliability is important. The importance of location to the APRS system has fueled development of a new generation of small low-power TNCs often integrated with a GPS module for use in mobile tracking stations. Not all AX.25 activity is APRS: Some AX.25 data networks exist, including the EastNet Packet Network mostly in the Northeastern United States and TARPN Network mostly in North Carolina. APRS digipeating protocols require specific naming conventions, and older TNCs may not have the required support to be used as a digipeater. However, almost any TNC can be pressed into service for Home or Tracker use. TNCs that were clones of the popular TAPR TNC-2 may be upgradeable via the UIDIGI firmware project.

TNC/Radio data ports

Although typically described as data ports, the interface between a radio and a TNC is almost entirely analog audio (plus lines for PTT and

squelch In telecommunications, squelch is a circuit function that acts to suppress the audio (or video) output of a receiver in the absence of a strong input signal. Essentially, squelch is a specialized type of noise gate designed to suppress weak s ...

). The connectors used for this purpose vary widely across TNC manufacturers, but modern radios that offer data ports have widely adopted the Mini-DIN 6-pin connector. Also used are full-size DIN connectors, DE-9 (

D-sub The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smallest connectors used on computer systems. Description, ...

) connectors, modular telephone (RJ) connectors, and combinations of mini- and micro-headphone connectors (typically on handheld radios). * 6-pin Mini-DIN

Terminal data port

TNCs were originally designed to accept messages from a human typing on a

. TNCs had a DB-25 or DE-9 connector carrying asynchronous start-stop bytes with

RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such as a compu ...

signal levels. This could also be used with the

serial port A serial port is a serial communication Interface (computing), interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in Pa ...

of a personal computer. Serial ports are now pretty much extinct, but USB-to-serial converter cables are available. However, typically a human uses a more sophisticated software package running on a personal computer that sends messages to the TNC using the KISS (TNC) protocol or the 6PACK protocol. Modern Software TNCs provide

TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are ...

interfaces that can be accessed across computer networks. For example, it is possible to run a software TNC on a

Raspberry Pi Raspberry Pi ( ) is a series of small single-board computers (SBCs) developed in the United Kingdom by the Raspberry Pi Foundation in collaboration with Broadcom Inc., Broadcom. To commercialize the product and support its growing demand, the ...

near the radio and access it from a laptop computer in another location. Software TNCs also provide " pseudo terminals" so they can be used with old applications that only know how to use serial ports.

References

External links