The purpose of the system architecture of the HF message system is to reduce the power and complexity of the mobile stations. This has led to the use of geographical diversity. Results are presented which show the effectiveness of this technique although further work is required to obtain values of 'correlatedness' to compare with previous work. The use of a software modem means that the mobile terminal consists of a low power HF transceiver with vertical whip antenna and an IBM PC clone with DSP card. This represents a very compact system which requires only modest operator skills.
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