HF data transmission - Lessons from the past, directions for the future

A development history and a projection of future prospects in design and performance are presented for narrow band HF data transmission systems. A multifrequency network employing wide band radio/modems made possible by microprocessor and VLSI technologies is proposed which will make possible the relaying of mesages so that they can be delivered to sites that cannot receive them directly from a source. The network requires a two-part routing algorithm; one part establishes routing tables, and the other forwards messages. This network must be periodically reinitialized in response to its abrupt change at sunrise and sunset, when the reflecting ionospheric ionization layer moves.