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  • Other Sources  (110)
  • COMMUNICATIONS AND RADAR
  • 1970-1974  (110)
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  • Other Sources  (110)
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  • 1
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    Technical requirements for radio equipment for communication between crews of space vehicles and stations (1971)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TT-F-13597 , NAS 1.77:13597
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    A new VOX technique for reducing noise in voice communication systems (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: A VOX technique for reducing noise in voice communication systems is described which is based on the separation of voice signals into contiguous frequency-band components with the aid of an adaptive VOX in each band. It is shown that this processing scheme can effectively reduce both wideband and narrowband quasi-periodic noise since the threshold levels readjust themselves to suppress noise that exceeds speech components in each band. Results are reported for tests of the adaptive VOX, and it is noted that improvements can still be made in such areas as the elimination of noise pulses, phoneme reproduction at high-noise levels, and the elimination of distortion introduced by phase delay.
    Keywords: COMMUNICATIONS AND RADAR
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    A baseline maritime satellite communication system (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This paper describes a baseline system for maritime communications via satellite during the 1980s. The system model employs three geostationary satellites with global coverage antennas. Access to the system is controlled by a master station; user access is based on time-ordered polling or random access. Each Thor-Delta launched satellite has an RF power of 100 W (spinner) or 250 W (three-axis stabilized), and provides 10 equivalent duplex voice channels for up to 1500 ships with average waiting times of approximately 2.5 minutes. The satellite capacity is bounded by the available bandwidth to 50 such channels, which can serve up to 10,000 ships with an average waiting time of 5 minutes. The ships must have peak antenna gains of approximately 15.5 dB or 22.5 dB for the two cases (10 or 50 voice channels) when a spinner satellite is used; the required gains are 4 dB lower if a three-axis stabilized satellite is used. The ship antenna requirements can be reduced by 8 to 10 dB by employing a high-gain multi-beam phased array antenna on the satellite.
    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
  • 4
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    Performance analysis of a frame sync algorithm for uncoded PSK telemetry (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The optimum procedure for locating a frame sync word periodically inserted in uncoded binary data received over a binary symmetric channel is based on the Hamming distance metric. In this paper, a practical frame sync acquisition and maintenance algorithm is described, and its performance is analyzed. Specifically, with respect to this algorithm, an upper bound on the probability of false sync acquisition, the mean time to sync acquisition, and the subsequent mean time to loss of sync are computed for arbitrary bit error rates, frame lengths, sync word lengths, and algorithm parameters.
    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
  • 5
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    Burst-error characteristics of the equatorial transionospheric channel (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Analyses of AGC analog data from the Small Astronomy Satellite (SAS) at VHF (136 MHz) have shown amplitude fluctuations in the signals received at several equatorial tracking sites operated by NASA. Errors in data are shown to increase markedly for nighttime satellite passes around the periods of the two equinoxes as compared to the errors observed during other periods. Qualitative and quantitative correlations are established between the ionospheric scintillation phenomenon and the occurrence of errors. Strong time and geographic cause-and-effect relationships are established by determining the statistical correlation between scintillation indices and bit error rates. Detailed analyses of the AGC fading statistics and the fine grain error statistics, such as the block-error distribution and the bit-error autocorrelation function, establish the strong correlation between deep fades and their effects on the burst error structure associated with the transionospheric channel and the communication receiver being employed.
    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
  • 6
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    Statistical modeling of scintillation effects (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Scintillation produces fluctuation of the complex envelope of a modulated signal. A useful way to characterize scintillation effects is to describe the signal statistics that result when a CW wave is transmitted through a random medium. Many theoretical treatments describe the signal statistics in a manner identical with the noise theory of Rice. These theories, however, predict Rice statistics only at a very great distance from the perturbing medium, and it has been suspected that generalization to permit the quadrature components of the scattered signal to be partially correlated Gaussian variates might better match the observed signal statistics. Recent tests of signals observed through three types of structured plasma have consistently confirmed this speculation and have revealed a surprising consistency in parameters describing the first-order signal statistics.
    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
  • 7
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    Synthesis and evaluation of phase detectors for active bit synchronizers (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Self-synchronizing digital data communication systems usually use active or phase-locked loop (PLL) bit synchronizers. The three main elements of PLL synchronizers are the phase detector, loop filter, and the voltage controlled oscillator. Of these three elements, phase detector synthesis is the main source of difficulty, particularly when the received signals are demodulated square-wave signals. A phase detector synthesis technique is reviewed that provides a physically realizable design for bit synchronizer phase detectors. The development is based upon nonlinear recursive estimation methods. The phase detector portion of the algorithm is isolated and analyzed.
    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
  • 8
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    Orbit-spectrum sharing between the fixed-satellite and broadcasting-satellite services at 12 GHz (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This paper identifies and evaluates strategies for sharing the geostationary orbit in the band 11.7 to 12.2 GHz between domestic systems in the fixed-satellite and broadcasting-satellite services. The effectiveness of two distinct types of sharing strategies, referred to as spectrum division and orbit division, is determined for various deployments of selected baseline systems representing the two services and for various combinations of sharing tactics such as frequency interleaving, crossed-polarization operation, and crossed-beam operation. Effectiveness is measured by the 'utilization factor', defined as the number of channels provided by the baseline systems when using an assigned share of the orbit-spectrum resource, relative to what they could provide if given the entire resource. Computer simulation is used to verify the intra- and interservice interference compatibility of the assumed deployments. It is concluded that total utilization factors close to 100 percent can be achieved with both spectrum-division and properly-chosen orbit-division strategies.
    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
  • 9
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    A Shuttle/SpaceLab RF environment survey facility (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This paper describes some of the basic system considerations of a proposed experiment for monitoring and measuring the global electromagnetic radiation environment. RF spectrum coverage for this spaceborne survey facility is anticipated to be quite broad and will include selected frequency bands ranging from UHF to millimeter waves. By establishing this RF environment survey facility, a broad data base of useful electromagnetic field intensity information will be developed. This, in turn, should help both the regulatory agencies and user community in terms of future frequency planning and system design by avoiding unwarranted interference. It is proposed that this experiment be flown as a future test bed during the Shuttle/Spacelab era for continuously gathering and updating information on earth-emitted electromagnetic emissions on a global scale.
    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
  • 10
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    A simulation of synthetic aperture radar imaging of ocean waves (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A simulation of radar imaging of ocean waves with synthetic aperture techniques is presented. The modelling is simplistic from the oceanographic and electromagnetic viewpoint in order to minimize the computational problems, yet reveal some of the physical problems associated with the imaging of moving ocean waves. The model assumes: (1) The radar illuminates a one-dimensional, one harmonic ocean wave. (2) The scattering is assumed to be governed by geometrical optics. (3) The radar is assumed to be down-looking, with Doppler processing (range processing is suppressed due to the one-dimensional nature of the problem). (4) The beamwidth of the antenna (or integration time) is assumed to be sufficiently narrow to restrict the specular points of the peaks and troughs of the wave. The results show that conventional processing of the image gives familiar results if the ocean waves are stationary. When the ocean wave dispersion relationship is satisfied, the image is smeared due to the motion of the specular points over the integration time. In effect, the image of the ocean is transferred to the near field of the synthetic aperture.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-X-72629 , 1974 USNC/URSI Meeting; Oct 14, 1974 - Oct 17, 1974; Boulder, CO; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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