Communications, Radar & Electronic Warfare (201.. - Index of

14 Communicatiom, Radar and Electronic Warfaresystems are also increasingly robust and have higher performance than legacy militarysystems. This now means that in some cases, military users are taking advantage ofcivil systems for their own uses. In many cases, civil systems and their ancillaries arecheaper than military alternatives and it can be more cost-effective to use cheaper,disposable handsets and having spares available.The same is also true in the other directions; who, now, does not use the GPS systemat least occasionally?The simple truth is that there are now an increasing number of cross-overtechnologies that are used for both military and civil applications. This makes therole of military communicators and spectrum managers far more complex as thereare a wider variety of systems available to use for particular circumstances.We will now look at technical aspects of the basic radio link.1.3 Factors Constraining Radio Communications1.3.1 The Basic Radio LinkRadio systems are dependent upon a number of intermediary elements, all of which arenecessary to ensure that the transmitted message is received correctly. Figure 1.7shows some basic blocks in the hardware part of the system. The transmitter is thesystem that receives or generates the message to be transmitted. It can'ies outconditioning, conversion and modulation of the signal into an RF electrical signal .For example, a mobile phone picks up voice from its microphone, converts the signalIsotropICantennaTransmittingantennagain (dBI)Propagation loss (dB).. ----------- .Transmission loss (dB).. ----------- .IsotropICantennaReceiVingantennagain (dBi)Transmittingantennalosses (dB)System loss (dB)+--------------ReceiVingantennalosses (dB)I ,, ,,L ____________T a o .:s d _____________Figure 1.7Bm,ic Jo& diagram, derived from ITU-R P.34J-1.