Ham Radio Basics
Menu
Digital Modes

Packet Radio for Hams

Packet radio sends data between computers over ham frequencies. Learn how AX.25, TNCs and Direwolf work, what you need to start, and where packet is still used.

Published 3 min read
On this page
  1. What packet radio is
  2. How it works
  3. What you need
  4. Software TNC setup overview
  5. What you can do with packet
  6. Frequencies and rules
  7. Is it still used?
  8. Related guides

What packet radio is

Packet radio is a way of sending computer data over amateur radio. Messages are broken into small packets, each with address information and error checking, and sent between stations. It was very popular in the 1980s and 1990s, before the internet became common, for bulletin boards, file transfers and email-like messaging. Today it has a smaller but dedicated community, and it also lives on inside other systems such as APRS.

How it works

  • AX.25: the protocol commonly used for amateur packet. It adapted a standard data-link protocol to include amateur call signs in each frame, which also helps meet station identification needs.
  • TNC (Terminal Node Controller): hardware that connects a computer to a radio. It converts data into audio tones and back, and handles the packet protocol.
  • Modulation and speed: on VHF and UHF, 1200 baud audio frequency-shift keying through an FM radio is the most common setup. 9600 baud is also used with radios that support it. HF packet generally runs at 300 baud and is much less common.
  • Digipeaters, nodes and BBS: digipeaters repeat packets to extend range. Nodes link stations together. A bulletin board system (BBS) stores messages and files for others to read.

Packet is a data mode with error correction. Lost or corrupted packets are re-sent, so reliable delivery is possible, though it can be slow on busy or noisy channels.

What you need

  1. An amateur license that allows data on the frequency you plan to use.
  2. A VHF or UHF FM radio with a data or audio connector, or a handheld with a suitable cable.
  3. A TNC, or a sound card interface plus a software TNC.
  4. A computer or a small single-board computer.
  5. Terminal or application software, depending on what you want to do.

Software TNC setup overview

Direwolf is a popular free software TNC that uses a computer sound card in place of dedicated hardware. A typical setup runs like this:

  1. Connect the radio’s audio output to the computer’s sound input and the computer’s sound output to the radio’s microphone input through an interface that also handles push-to-talk.
  2. Install Direwolf and edit its configuration file to name your sound device, call sign and, if needed, a push-to-talk method.
  3. Start Direwolf and watch for decoded packets. A good test is to listen for local traffic before transmitting.
  4. Connect client software through a KISS or AGWPE interface, depending on the program.
  5. Adjust audio levels carefully. Overdriving the radio gives poor results and may disturb others.

Follow the project’s current documentation, because settings and defaults change between versions.

What you can do with packet

  • Read and post messages on a packet bulletin board where one still exists.
  • Use APRS, an application that sends position, weather and short messages using AX.25 unnumbered frames. In North America, APRS commonly uses 144.390 MHz, but other regions use different frequencies.
  • Send email through gateway systems such as Winlink in some configurations. Other modes may be better suited to emergency messaging in many areas; see ham radio EMCOMM.
  • Experiment with digipeaters, nodes and linking between stations.
  • Plot APRS positions with ham radio mapping software.

Frequencies and rules

Packet segments are defined in band plans and differ by region. Use only frequencies that your band plan allocates to data, and listen before transmitting. Data signals should not be placed on repeater inputs or voice channels. Each station must identify with its call sign as required by local rules.

Is it still used?

Yes, though activity varies a great deal. Some regions have an active packet network or APRS network, and others have almost nothing. Before buying equipment, listen for local packets, check regional clubs and read recent forum posts to see what is active near you.

Packet-style data is one way to build networks. For higher-speed alternatives using Wi-Fi-class hardware or LoRa, see mesh network ham radio. If you want to know what a packet burst sounds like on the waterfall, check digital mode identification by sound.

The complete guide to digital modes

Ham Radio Digital Mode Identification by Sound and Waterfall
Read the guide

Keep exploring

Guides from other topics

All topics →