Packet Radio

The data stream generated by a computer can be trasmitted on the air as easily as it is on the telephone wires.
The data is divided into small blocks (packets) containing also the origin and destination addresses. The modulation used in this case is FSK or AFSK, with bandwidth ranging from 200 to 1,000 Hz or more.
There are many protocols in use, but the most popular are AX.25 (derived from X.25 of wired networks) and TCP/IP, the same used on the Internet.