Space-Based Broadcasting The Future of Worldwide Audio Broadcasting (1985) / Chapter Skim
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Introduction
Introduction
Pages 2-10
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From page 2... ...
VOA audio programs broadcast at HF are di rected to l i steners located great distances from the VOA broadcasting transmitter sites. With the exception of the lowest part of the ME band and even lower frequencies, the range of radio signals transmitted via the Earth's atmosphere and surface or ground-wave propagation that can be easily and usefully received is limited to a few hundred miles from the transmitter.
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From page 3... ...
These trends burden many broadcasters, who face increased financial costs, increased need for more effective transmitting sites, increased professional engineering and operating demands, and increased interference to their signals by the signals of other broadcasters that arrive 2. Radio frequency power X antenna gain relative to an isotropic radiator.
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From page 4... ...
The radiowave propagation characteristics of the ionosphere often allow jamming signals to interfere with the reception of programs broadcast on these frequencies within countries located far from the areas being jammed. These circumstances and trends have caused a sharp increase in the level of nonnatural interference to HE shortwave signals broadcast over much of the world, and growing problems in allocating and using available frequencies.
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From page 5... ...
Inherent complexity in identifying truly useful operating frequencies, and in reaching acceptable multicountry agreements to their specific allocation and proper use 2. Limits on the range of signal distance created by the geometry of the Earth's surface and its ionospheric layers When audiences to be served are located beyond the approximately 2,000-mile maximum one-hop signal distance from a shortwave transmitter, repeater transmitters must be located in other countries sufficiently close to the audiences.
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From page 6... ...
Signals radiated in directions other than the direction of the intended audience area (i.e., signals that are also always radiated from the broadcasting transmitter antenna's sidelobes and backlobes, even though of lesser intensity than those radiated from its main lobed also may cause interference to additional audiences distributed over great areas. Indeed HE shortwave transmitters and their antennas, the Earth's surface, and the ionosphere are dull and fuzzy tools for focusing audio broadcasting signals efficiently onto specific listening audiences.
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From page 7... ...
and operations and maintenance (O&M) required to maintain an acceptable broadcasting service encompass increasing a broadcasting system's effective radiated power, the number of simultaneous transmissions on different radio frequencies, and extra-country repeater transmitter sites.
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From page 8... ...
Perhaps the greatest longterm threat to the effectiveness of any surface-based shortwave audio broadcasting service is the gradual loss of audience share. Several factors make this threat a read possibility, including continued efforts by many countries to increase their use of great effective radiated power and multiple simultaneous frequency broadcasting, raising the general susceptibility of received signals to degradation.
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From page 9... ...
Initial estimates are made of their acquisition and ongoing financial costs, and observations are made regarding how these costs could be met. Although many radiowave bands may be used for broadcasting and/or for space-related communications, at present there are no bands set aside by international agreement to be used specifically for broadcasting audio signals from space directly to individual, not community, surface receivers.
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From page 10... ...
, hovering over a selected surface area for a year or more or forever. They would receive power to drive their electric engines and support their payloads via a collimated microwave beam of electrical energy directed upward to them from the Earth.
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