Space-Based Broadcasting The Future of Worldwide Audio Broadcasting (1985) / Chapter Skim
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Section 3: The Space Segment (Transmitter) - Surface Segment (Receiver) Power Budget for a UHF DBS-A System-Service
Section 3: The Space Segment (Transmitter) - Surface Segment (Receiver) Power Budget for a UHF DBS-A System-Service
Pages 23-35
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From page 23... ...
~ It should be appreciated that while the technological and operational characteristics suggested here are rational, reasonably well informed, and adequate for an initial paper addressed primarily to other communications engineers, these characteristics are neither comprehensive nor described in the detail required for space and communications system engineering. Correcting errors of facts and/or judgement and "putting flesh on the bones" must be the challenge to, and the responsibility of, others.
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From page 24... ...
As a first, somewhat arbitrary but reasonable, estimate the following building structure attenuation circumstances are assumed: o On average, 25~ percent of all receivers at all times will experience essentially no radiowave attenuation beyond the inverse distance-squared free space path loss. O On average 25 percent will experience 3 db.
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From page 25... ...
The Influence of Tropospheric Rainfall Even at the 99.9~+ reliability level, it does not appear necessary to consider providing more than a fraction of a db to accommodate excess signal attenuation in tropospheric rainfall conditions. Attenuation Caused by the Total of Building Structures Plus Foliage Over the large broadcast area expected to be served by any one space segment (some 7.5 million square miles; some 20 million square kilometers)
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From page 26... ...
Considering all demands for space segment power, the peak DC power level will probably have to be in the kilowatt range, and this margin-cost balance is a particularly important consideration. Under many receiver location circumstances, considerable accommodation to such additional losses can be obtained through increased receiver antenna gain, at the cost of increased directivity restrictions, through increased receiving antenna heights, at the cost of reduced receiver transportability; and by accepting a lower receiver S/N, at the cost of reduced quality of reception.
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From page 27... ...
Indeed, the matter of excess radiowave path loss is fundamental to any consideration of employing the electromagnetic spectrum for a UHF DBS-A ~system, and it requires careful and comprehensive experimental and statistical study. Frequency Selective Fading There is little reason to imagine that any of the signal fading circumstances previously outlined would result in important frequency selective fading across the bandwidth of interest in this suggested system design.
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From page 28... ...
The circuit performance required to provide the three different service qualities are Basic Service, Standard Service, and Superior Service. Basic Service.
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From page 29... ...
This quality of service would be available (at a user price higher than the Standard Service price) to any broadcaster who wished to reach an audience served by other competing high-qua~ity electronic communications media.
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From page 30... ...
lo. Loss in converting the space segment's DC power to transmitter RF power output, assuming solid state final stages, and including line losses from the final power amplifiers to the antenna feeds, power required for the power amplifiers' driver stages, power for the receiver to receive signals from the surface feeder station; power consumed by the switch; and general spacecraft housekeeping demands = 5 db.
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From page 31... ...
watt DC/5 kHz channel/ standard unit surface area. The total DC power required for Basic Service for an entire regional system -- one employing a single space segment with the maximum product of channels X the number of beams expected to be in use at any one time = 23,000 -- is (Owl (23,000)
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From page 32... ...
The power requirements for Standard Service, per channel, per standard coverage area follow: The channel width of 60 kHz = 48 db referred to ~ Hz (i.e., there would be 4 db more receiver input noise power than for the Basic Service)
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From page 33... ...
Recalling that OR = lS db (i.e., 5 db more than that assumed for the Basic and Standard Services) the net power increase required = + ll db - 5 db = + 6 db referred to the Basic Service.
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From page 34... ...
could be used and increased space segment radiated power employed in order to maintain the Standard Service S/N (again, keeping maximum allowable surface flux density limits in mind)
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From page 35... ...
WORKING PAPER 0.25 watt for Standard Service, a relatively small overall increase in space segment power (a ~ db increase in peak space segment power would be somewhat more than 1000 watts) could allow a large increase in the number of channels in those relatively few areas where they would be needed.
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