ABSTRACT
Terrestrial communication within the GMDSS involves the transfer of information which exists in one or more different modes—voice, telex (telegraphy), facsimile and data. The raw baseband signals, for these modes, are modulated onto the carrier frequency for propagation, using one of a number of modulation methods—amplitude modulation (AM), frequency modulation (FM) or phase modulation (PM). As with all electronic systems, valued judgements must be made when considering the relative advantages and disadvantages of using one modulation system in preference to another. The design choice of the modulation method to be used in a communications system is based on a number of factors, but for the purpose of this book it is essentially the signal power, the bandwidth and the noise which are to be considered.
