System Design Considerations
The purpose of this paper is not to discuss the system elements, but to describe important topics in system design and analysis. The nature of speech and hearing is reviewed, and speech intelligibility and the articulation index (Al) are given precise definitions. The effect of speech clipping on these characteristics is discussed. Section 2.1 continues with an exposition of signal representations and Hilbert transforms, leading into the various forms of AM, including SSB. For completeness, and to form a basis of comparison with SSB, angle modulation is also discussed. Finally, a comparison is made between the various forms of AM and FM. Section 2.2 covers collocated system designs. The various factors that cause problems in simultaneous operation of receiver and transmitter are discussed. These include transmitter out-of-band noise and distortion, receiver distortion and reciprocal mixing, and transmitter back-IM distortion. One of the reasons for a resurgence of interest in HF radio transmission by the military services is its use as a backup to satellite communications. To meet modern needs for communication in a potential jamming environment, such equipment must be designed to incorporate electronic counter-countermeasures (ECCM). Those elements of ECCM design that affect the SSB receiver and transmitter are discussed in section 2.3.
System Design Considerations, Page 1 of 2
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