Packet Radio is another error-free mode, which has added advantages of higher speed (if good radio signal is available) and increased economy of spectrum by time-sharing a channel with other users.

Transmitted text is collected into "packets" before sending. Within this packet is the callsign of the packet destination, the source (i.e. sender's) callsign, control information on the type of packet being sent (control, acknowledgement, information), data (where applicable), and a CRC (Cyclical Redundancy Check) which enables the receiver to determine whether there are any errors in the received packet.

The exact format of the packet is laid down by an agreed protocol. The first protocol widely used by amateurs was known as the VADCG V1 protocol. While this protocol facilitated early experimentation, it had a number of limitations.

To overcome these limitations, a new protocol called AX.25 was developed. AX.25 is based on X.25, a commercial computer communications protocol. Packet radio requires the use of a computer to handle the protocol and the exchange of data. This may be done by either programming a personal computer, or by using a dedicated computer called a TNC (Terminal Node Controller) connected between a computer/terminal and the radio.

The TNC approach leaves the operator's computer free to handle application activities. A hybrid system that uses software and a computer I/O card is another alternative that has benefits of both the programming approach and the TNC approach. Packet Radio has traditionally been used at data rates of 1200bps using ASFK modulation. With advances in applications and technology this has become a rather limiting factor, and 9600bps operation is becoming more common. Higher speeds are also becoming used on higher bands for networking applications, and speeds of 19200bps through to 2Mbps are becoming more common.


Frequencies:

300 Baud. 500 Hz wide. 200 WPM. 8 Bit. 3.620-3.635, 10.140-10.150, 14.095-14.0995, 18.105-18.110, 21.100-21.110, 24.925-24.930.