Text Messaging with Amateur Radio
Before the computer there were several modes of transmitting text messages by Radio. The first was the use of Morse Code or CW (Continuous Wave) where the signal was sent letter by letter in a series of coded long and short signal bursts. This was done by hand and an expert could reach a speed of up to 60 words per minute. this mode. (Although outdated by modern development CW is one of the most efficient modes in terms of information transfer and bandwidth used). CW Speeds were increased and skill needs reduced by pre-recording the CW signal on paper tape and playing it at higher speeds to be recorded by the receiving station. Then came the inevitable demand for even faster and more accurate text message transfer. and the radio teletype came into being.
Radio Teletype or RTTY
The radio teletype was a development from the teletype that had been developed to send text messages by wire .. The teletype came into commercial use in the 1920’s and was essentially an electric typewriter sending signals down a wire using a five bit code – the Baudot Code. This code restricted the machine initially to 32 characters but with the use of shift keys this could be increased. When a key on the radio teletype keyboard was operated, a specific Baudot Code was transmitted for reception and decoding at the receiving machine . By the 1940’s teletype was the major method of distributing text in the newspaper world.
Radio Teletype, or RTTY as it is commonly called today (Radio Teletypwriters), was in commercial operation in 1932 and is still actively used by amateurs and others today. Developments include the wider use of the 7 bit ASCII Code ( American National Standard Code for Information Interchange) to replace the more limited 5 bit Baudot Code. Most HF amateur radio transceivers are equipped to transmit and receive RTTY mode. Keyboard to keyboard chats are usual for the RTTY enthusiast and it is a popular mode for digital Dx’ing The electomechanical systems of the past have now been replaced by the computer and the need for a printout replaced by the computer screen. The use of the computer has also allowed the introduction of software able to produce more accurate and speedier text messaging
The earlier RTTY sytems consited of a a teletype machine, a modem and a radio. The modem is an electrical device for converting the digital signals from the teletype into audio tone which then is passed to the radio to transmit the signal to a receiving station where the signal is converted back to a text message. Today such functions can be performed with modern computers equipped with digital signal processors or sound cards. The sound card performs the functions of the modem and the computer CPU performs the processing of the digital bits.
Packet radio is a mode of text communication invented in the 1970’s by workers at the University of Hawaii. The mode became very popular in the 1980’s and later before the advent and general use of computers with their increasingly powerful software capabilities.. It is still widely used for transmitting messages and maintaining Bulletin Boards. A major application today for the amateur packet radio configuration is in relation to Automatic Position Reporting System (APRS.) where it is used with a GPS (Global Positioning System) receiver so that positional information can be transmitted.
Packet radio breaks the message into groups or packets with error correction to produce error free data transfer. Packet has the advantage over methods such as RTTY in that it can store messages as for instance in a Bulletin Board application to allow retrieval at a later time be the receiving station. Packet radio is an efficient users of the radio spectrum.
Packet radio uses a terminal mode controller (TNC) which is a small computer based system specially designed for packet work, Some of its functions are similar to the modem described for RTTY systems but the TNC performs other logic functions including sorting the message into packets. While often the TNC was a small separate box connected to the radio, today it is increasingly common to use PC software TNC emulation with an internal or external modem
Packet radio operates typically on the HF and VHF bands
PSK31 and others
As is inevitable in our age of technological development, Packet Radio soon led to advances designed to overcome problems found by experience and to use the opportunities of the power of computer software manipulation of data and signals..
Systems such as Pactor and Clover were designed to improve the quality of data sent through potentially noisy radio channels such as are found in long distance HF transmissions.
At present an increasingly popular mode is PSK31 developed by amateur Peter Martinez G3PLX (UK) for real time keyboard to keyboard QSO’s PSK refers to Phase Shift Keying modulation used in the system. PSK31 is computer based with sound card s well as the transceiver system to transmit and receive signals