• Understanding & Specifying Hi-Density Digital Recording Systems

      Schulze, Glen H.; Bell & Howell (International Foundation for Telemetering, 1977-10)
      Rapid advancement of hi-density digital recording technology has left most user organizations in a confused and bewildered state with respect to understanding and, more importantly, specifying hi-density recording systems. Users attempting to acquire advanced hi-density hardware either without procurement specifications or with incomplete or shallow specifications will probably gain the needed experience too late, after an unusable system has been delivered. Several prominent user facilities have recently bought and accepted hi-density recording hardware and immediately been forced to retire the equipment from use to avoid disastrous embarrassment. Other users have had to redesign accepted equipment before it could be used. One user who blindly accepted a proposal to convert several newly ordered analog recorders to a digital format had to remove and dispose of the digital electronics after delivery and revert back to analog methods. The ability to professionally specify and technically monitor a hi-density recording system contract can only be based upon a thorough understanding of the high density digital coding, recording, reproducing and decoding process. The purpose of this paper is to identify and discuss the more important elements of this emerging technology for users who suddenly find themselves needing this capability.
    • Underwater Optical Beam Tracking

      Gagliardi, R. M.; University of Southern California (International Foundation for Telemetering, 1977-10)
      The use of blue-green laser frequencies for establishing an air ocean underwater communication channel has been well accepted. However any attempt to initialize or maintain such a link will invariably require some method of accurately spatially pointing and tracking the penetrating beam. In this paper we present results of a study concerned with determining the ability to spatially track an optical after undergoing underwater propagation. By invoking the concept of modulation transfer theory and substituting established propagation models for underwater coherence functions, the focal plane intensity patterns generated in wide angle optical lensing systems can be determined, as a function of the link characteristics (e.g. sea state, depth into the ocean, turbulence, etc.).With the intensity pattern modeled, the behavior of various forms of optical trackers can be analyzed by the application of standard tracking loop theory. Of particular interest here is the application of well known mathematical tools, such as Kolmogorov theory, which allows generalized statistical analysis to be performed on both linear and nonlinear dynamical systems. The result of such an approach is the development of a differential equation whose solution yields the statistics of the tracking error. Theoretical studies of this type have been examined previously for generalized scattered optical fields [1]. With these basic approaches as a guide, mean squared tracking errors can be derived, which assesses the perfomance of the beam tracker in relation to the channel characteristics.
    • VHF Adaptive Array Test Results

      Zeger, Andrew E.; Burgess, Lawrence R.; General Atronics Corp. (International Foundation for Telemetering, 1977-10)
      A four-element Anti-Jam Antenna Array (AJAA) system has been built to provide protection for U.S. Marine Corps inter-command post communications in the 30-76 MHz band. A unique and important feature of the AJAA system is its ability to spatially null jammers down to a level below that of the desired signal. This capability and the prevention of accidental cancellation of the desired signal is achieved by using the desired signal's direction-of-arrival (DOA) in a prebeamformer located ahead of the adaptive beamformer. A positive S/J at the array output is required to prevent capture by a co-channel interference in standard FM field radios. Antenna range tests were performed on the AJAA system using AN/PRC-77 radios as far-field signal and jamming sources. Results of these tests show that the AJAA provides an intelligible FM voice signal at its output while simultaneously suppressing three jammers.