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  • 1
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    Beam waveguides in the Deep Space Network (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A beam waveguide is a mechanism for guiding electromagnetic radiation from one part of an antenna to another through a series of reflectors. Appropriate placement of reflectors on an antenna allows a beam to be guided around the elevation axis and/or below the alidade. The beam waveguide permits placement of all electronics in a room on the alidade below the elevation axis, or below the alidade; feed horn covers to be protected from the weather; and feed electronics to be in spacious rooms rather than in crowded cones, and always level rather than tipping with change in elevation angle. These factors can lead to lower costs in implementation such as Ka-band, better antenna performance at X-band, more efficient and stable performance of transmitters and receivers, and lower maintenance and operating costs. Studies are underway to determine methods for converting the major antennas of the Deep Space Network (DSN) to beam waveguide operations by 1995.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 174-182
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Ka-band (32-GHz) downlink capability for deep space communications (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The first quarter century of U.S. solar system exploration using unmanned spacecraft has involved progressively higher operating frequencies for deep space telemetry: L-band (960 MHz) in 1962 to S-band (2.3 GHz) in 1964 to X-band (8.4 GHZ) in 1977. The next logical frequency to develop for deep space is the Ka-band (32 GHz) for which a primary deep space allocation of 500 MHz between 31.8 to 32.3 GHz was established in 1979. The telecommunications capability was improved by a factor of 77 (18.9 dB) through the frequency changes from L-band to X-band. Another improvement factor of 14.5 (11.6 dB) can be achieved by going to Ka-band. Plans to develop and demonstrate Ka-band capability include the continued measurement of weather effects at Deep Space Network (DSN) sites, development of a prototype DSN ground antenna and supporting subsystems, augmentation of planned spacecraft with Ka-band beacons, and development of spacecraft prototype modules for future Ka-band transmitters. Plans for augmenting the DSN with Ka-band capability by 1995 were also developed. A companion set of articles describes the Ka-band performance and technology in greater detail.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 96-103
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    A growth path for deep space communications (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Increased Deep Space Network (DPN) receiving capability far beyond that now available for Voyager is achievable through a mix of increased antenna aperture and increased frequency of operation. In this note a sequence of options are considered: adding midsized antennas for arraying with the existing network at X-band; converting to Ka-band and adding array elements; augmenting the DSN with an orbiting Ka-band station; and augmenting the DSN with an optical receiving capability, either on the ground or in space. Costs of these options are compared as means of achieving significantly increased receiving capability. The envelope of lowest costs projects a possible path for moving from X-band to Ka-band and thence to optical frequencies, and potentially for moving from ground-based to space-based apertures. The move to Ka-band is clearly of value now, with development of optical communications technology a good investment for the future.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 120-125
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Satellite personal communications system (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Voice channel communication between low power mobile stations dispersed over a large area is provided by a system which includes a geostationary satellite utilizing a large UHF antenna that can receive a transmission from a caller and retransmit it over any one beam of a matrix of narrow beams, so the chosen beam covers an area in which a designated called party is located. A single up-link control channel occupying a narrow frequency band, can be utilized to receive dial up signals from a caller, and another single down link control channel can be utilized to ring up the called party located anywhere within the continental United States. The satellite antenna includes a matrix of feed horns that not only direct the beams in a controlled matrix onto the area of the continental United States, but also permit detection of the region from which the caller's signal is transmitted and the region from which the called party's answer is received, to enable the interconnection of signals received from these two regions. The system is particularly useful for rural areas.
    Keywords: COMMUNICATIONS AND RADAR
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Alternate symbol inversion for improved symbol synchronization in convolutionally coded systems (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Inverting alternate symbols of the encoder output of a convolutionally coded system provides sufficient density of symbol transitions to guarantee adequate symbol synchronizer performance, a guarantee otherwise lacking. Although alternate symbol inversion may increase or decrease the average transition density, depending on the data source model, it produces a maximum number of contiguous symbols without transition for a particular class of convolutional codes, independent of the data source model. Further, this maximum is sufficiently small to guarantee acceptable symbol synchronizer performance for typical applications. Subsequent inversion of alternate detected symbols permits proper decoding.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications; COM-28; Feb. 198
    Format: text
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  • 6
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    Offset quadrature communications with decision-feedback carrier synchronization (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: In order to accommodate a quadrature amplitude-shift-keyed (QASK) signal, Simon and Smith (1974) have modified the decision-feedback loop which tracks a quadrature phase-shift-keyed (QPSK). In the investigation reported approaches are considered to modify the loops in such a way that offset QASK signals can be tracked, giving attention to the special case of an offset QPSK. The development of the stochastic integro-differential equation of operation for a decision-feedback offset QASK loop is discussed along with the probability density function of the phase error process.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications; COM-22; Oct. 197
    Format: text
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  • 7
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    Carrier synchronization and detection of QASK signal sets (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A carrier regeneration loop which generates highly coherent quadrature reference signals for quadrature amplitude-shift keying (QASK) demodulation is presented. The loop employs the principle of decision feedback and has a structure analogous to a decision feedback loop for quadriphase signals suggested earlier in the literature. The error probability performance of QASK is computed in the presence of the noisy carrier reference signals provided by the above loop. It is demonstrated that when the ratio of data rate to loop bandwidth is 50 or greater, then for all practical purposes, ideal QASK error probability performance is achieved.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications; COM-22; Feb. 197
    Format: text
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  • 8
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    A national voice network with satellite and small transceivers (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A geostationary satellite utilizing a large multiple-beam UHF antenna is shown to be potentially capable of providing tens of thousands of voice channels for hundreds of thousands of mobile ground terminals using hand-held or vehicular-mounted transceivers with whip antennas. Inclusion of on-board network switching facilities permits full interconnection between any terminal pair within the continental United States (CONUS). Configuration tradeoff studies at selected frequencies from 150 to 1500 MHz, with antenna diameters ranging from 20 to 200 m, and CONUS-coverage multiple beams down to 0.3 deg beamwidth, establish that monthly system user costs in the range of $90 to $150, including leased and maintained ground equipment, are feasible.
    Keywords: COMMUNICATIONS AND RADAR
    Type: AIAA PAPER 78-626 , Communications Satellite Systems Conference; Apr 24, 1978 - Apr 27, 1978; San Diego, CA
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Spectrally efficient modulation (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Spectrally efficient modulation, involving the maximization of the transmitted data rate through a specified bandwidth, may aid in alleviating the problem of spectral congestion in the electromagnetic spectrum. Attention is given to pulse-shaping and nonbinary modulation, and particularly to combined amplitude- and phase-modulation. Theoretical performance limits, such as Shannon's bound, are used to assess the effectiveness of the systems described. Consideration is also allotted to spectrally efficient modulation for terrestrial microwave systems, required to provide 1000 voice channels in the 4- and 6-GHz band.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Conference on Communications; Jun 12, 1977 - Jun 15, 1977; Chicago, IL
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Transmitter efficiency considerations in MAPSK signal selection (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A simple model of the efficiency-power relationship for a microwave transmitter permits comparison of M-ary amplitude and phase shift keyed (MAPSK) signal array performance on the basis of average DC power in, rather than average RF signal power out. This is of interest in comparing MAPSK arrays with comparable polyphase, since the polyphase transmitter is operated at a single power level, while MAPSK varies over a range of power levels, each of differing efficiency. A constant efficiency-power curve permits comparison of signal arrays in terms of array average power, while a linear curve requires comparison on the basis of array peak power. Since typical efficiency curves will lie between these extremes, the array peak and average power levels provide bounds on array requirements for average DC input power. Examination of the performance of several MAPSK sets reveals a distinct power advantage of quadrature amplitude shift keying (QASK) over most viable signal sets.
    Keywords: COMMUNICATIONS AND RADAR
    Type: National Telecommunications Conference; Dec 02, 1974 - Dec 04, 1974; San Diego, CA
    Format: text
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    NASA TECHNICAL REPORTS
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