A terminal node controller is a piece of equipment amateur radio operators use to send and receive data on their computers through radio frequency. Radio operators that utilize a terminal node controller can only participate in Amateur X.25 (AX.25) packet radio networks. AX.25 is a communication protocol specifically designed for amateur radio operators that helps with efficient data transfer.

Think of a terminal node controller as a modem someone uses to connect to the Internet. It acts as a translator between your computer or phone and Internet cables. The difference is that a terminal node controller facilitates communication through an assigned radio frequency, not over the Internet.

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Read More about a “Terminal Node Controller

A terminal node controller is typically associated with radio amateurs or ham radios. But don’t let the word “amateur” fool you into thinking that it is only used for entertainment.

The Importance of Radio Amateurs

Amateur radio operators, also called “radio amateurs” or “hams,” were among those picked during World War II, as they already had the knowledge and experience to operate communication technology. Therefore, the government didn’t have to train them, saving time and effort. The same logic holds true for any other national conflicts that may occur in the future.

During natural disasters, all other forms of communication may become unavailable, as cellular towers and satellites get damaged. But ham radios powered by a terminal node controller would still be available during these times.

Ham radios are also utilized in schools to help increase children’s interest in science and technology. Radio amateurs are also instrumental in developing more advanced technologies, such as cellular phones, satellite communications, television, and broadband. The only reason why they are called “amateur radio operators” is that they are not legally allowed to receive payment in exchange for their services as radio operators.

How a Terminal Node Controller Works

A terminal node controller works as a translator between a computer and the radio operator. In a nutshell, this is what happens in a packet radio network: Two radio amateurs, Oscar and Sheila each have their computers, terminal node controllers, and radios. All these devices are up and running.

  • Oscar types in the message, “Hello world,” on his computer.
  • Sheila’s radio receives the message and feeds it to her terminal node controller.
  • Sheila’s terminal node controller converts the tones in a format that the computer can understand, that is, in zeroes and ones.
  • The terminal node controller sends the converted message to Sheila’s computer, where it is converted back to the text, “Hello world.”

Are you wondering how this works in real life? Watch this video of a demonstration of using a terminal node controller:

What Is Inside a Terminal Node Controller?

A terminal node controller commonly has three major components that facilitate packet sending and receiving. These are:

  • Packet assembler and disassembler (PAD): Turns data into a packet so it can easily be transmitted.
  • Modem: A terminal node controller has a modem inside it, which converts the original message into zeroes and ones, and back again on the receiver’s end.
  • Logic chip: Programmed to obey the AX.25 protocol that ensures efficiency throughout the communication process. For instance, packets are received in the correct order they were sent because of the logic chip.

All these essential parts fit into a box that resembles an Internet modem. Below is a sample image of a terminal node controller, specifically the MFJ TNC-X Packet Controller.

Source: http://manuals.repeater-builder.com/MFJ/MFJ-1270X/MFJ-1270X%20Manual%20V2.pdf 

A terminal node controller makes it possible to send text messages from one computer to another without an Internet connection. As such, it is very handy during critical times, such as during or after disasters and wars.