Space-Based Broadcasting The Future of Worldwide Audio Broadcasting (1985) / Chapter Skim
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Section 2: Specific Consideration of UHF DBS-A System-Service
Section 2: Specific Consideration of UHF DBS-A System-Service
Pages 17-22
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From page 17... ...
In the UHF system-service design outlined here, very large channel capacity and very small unit surface coverage areas are assumed; they are inherently required by any eventual global system-service. Their actual dimensions could be achieved but only by using technology not now expected to become available in much less than a decade.
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From page 18... ...
Using these beams, near rea1-time knowledge of the signal transmission and noise circumstances, and dynamic power control among the individual subtransmitters would allow a sophisticated statistical approach to minimizing space segment peak power in the face of large temporal variations in channel capacity demands; the influence of the ionosphere that can cause scintillation-type signal fading, physical structures, foliage and terrain roughness on radiowave path loss; and other variations in noise levels external to the surface receivers. In view of the narrowness of the beams and the need to assure that desired audience areas are properly illuminated, care would have to be taken in l3.
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From page 19... ...
and with a total of some 30 million square surface miles (80 million square kilometers) to be served on a worldwide basis, on average each would have to deliver an adequate radiowave flux density to the surface over an area of some 7.5 million square miles (20 million square kilometers)
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From page 20... ...
The RF power delivered to each beam also would be controlled by the surface feeder station in order to provide a higher or lower than nominal flux density to some areas at some times. This control capability would preserve an appropriate quality of service in the face of changing program-channel-service quality demands and accommodate excess radiowave path loss associated with different areas served, season, weather, and ionospheric conditions.
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From page 21... ...
The maximum base bandwidth required to be transmitted would be 300 multiplexed audio channels each at least 5 kHz wide (as many as lO percent of the channels could be 15 kHz wide) to be delivered to each of four space segments simultaneously, i.e., the rough equivalent of two standard television channels to be transmitted upward over a 23,000-mile, ire-of-sight path.
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From page 22... ...
Such an antenna would have a ha~f-power beamwidth of some 25° and a gain of some lS db re isotropic, inclusive of a modest cable loss. In particularly difUcult terrain or in the presence of urban building signal "shadowing" where there could be significant additional diffraction field propagation loss, reception would be improved by elevating the antenna.
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