Digital modes have been around since RTTY but really took off with the computer generation. To oversimplify digital modes use the off-on (binary 0-1) to send information. CW is really a form of this although quite rudimentary. Most digital modes require a computer to be interfaced with the radio to assist with sending and receiving the data. Most also require a TNC (terminal node controller) with a chip that supports the particular mode. You send by tying on a keyboard and receive by viewing the information received on the screen. Some of the more popular digital modes are:
- RTTY – Radioteletype (RTTY) uses a baudot (5 bits per character) or ASCII code (7 bits per character) to communicate. RTTY is almost as reliable as CW and there are many hams who use this mode on a regular basis on the HF bands.
- Packet – uses the complete ASCII character set which permits both upper- and lowercase characters in a transmission. Packet is error-free which is achieved by sending data in small packets with a check bit. If an error is detected by the receiving station it replies and requests that the packet be resent. This is repeated as needed to receive the packet correctly. When signals are good a packet rarely needs to be sent twice but under poor conditions the resending of error packets slows down the exchange of information.
- Tor Modes – TOR means “teleprinting over radio.” These modes include AMTOR, Pactor, G-TOR and Clover. Basically they all use some variation of the technique mentioned in packet for ensuring error-free transmission. Each use specialized algorithms for transmission resulting in improved speed and accuracy.
- PSK-31 – is a relative newcomer to the digital scene and is fast becoming a primary digital mode. One reason for its appeal is that it uses the sound card in the computer to send and receive through the radio. No other special equipment is needed. PSK-31 uses very little bandwidth, less than CW and can function very well at low signal strengths. Unlike Packet and TOR it is not error-free.