• The Apollo VHF Ranging System

      Nossen, Edward J.; Government Communications Systems RCA (International Foundation for Telemetering, 1977-10)
      Redundancy of functions on manned space flights has been an important concept for crew safety. However, a redundant system generally implies doubled weight - a luxury that can not easily be afforded on a spacecraft. The Apollo Command Module- Lunar Module rendezvous mission was performed with the rendezvous radar system. RCA developed a VHF Ranging System, which permitted the voice/telemetry radios to be adapted as a backup for the radar's ranging function at relatively low additional weight. The proven accuracy and reliability of the VHF Ranging System resulted in its selection as the sole rendezvous sensor for subsequent earth orbital manned missions. The constraints imposed by existing radios are discussed, the ranging options and selected implementation are described, and the system accuracy is reviewed.
    • ECM/ECCM Effects on Voice Transmissions

      Buskirk, Ronald L.; Nossen, Edward J.; Government Communications Systems (International Foundation for Telemetering, 1977-10)
      An evaluation methodology for conventional and ECCM voice communications is presented, wherein intelligibility of the received message rather than error rate or signal-to-noise ratio is the quantity measured. This allows the engineer to include the psychoacoustic phenomena of a human listener in his system design considerations. Analyses have been performed which allow transformation of speech articulation test results into data more meaningful to the communications engineer. Since message intelligibility is established after baseband reconstruction of the voice signal, this method is universally applicable to most voice transmissions. It is insensitive to the nature of the medium, modulation, and interference sources. Examples are presented showing applications of these guidelines to the design of frequency hopping radios. Tests run on a simulator confirm the analyses. A sample tape is available to demonstrate some of the effects.
    • Pseudo-Random Code Sidelobe Canceller

      Haber, Conrad H.; Nossen, Edward J.; Government Communications Systems RCA (International Foundation for Telemetering, 1977-10)
      During acquisition of direct sequence pseudo-noise signals, time sidelobes are produced at the correlator output which will degrade detection performance. These sidelobes may be the result of additive noise, channel distortions, deliberate jamming or the non-ideal correlation function of truncated code sequences. In order to minimize these sidelobes, special codes can be selected based on their low sidelobe levels, or some special sidelobe reduction or cancellation algorithm may be devised. A sidelobe cancellation algorithm for use with LSI correlators has been simulated. Segments of a maximum length code word as well as a totally random bit stream were tested. The simulation results show that the largest sidelobes are reduced by a small amount; however, the majority of the sidelobes are reduced by as much as 6 dB. Consequently the false alarm rate for a particular threshold setting may be reduced. A compatible technique for the derivation of a CFAR reference from the same correlator was also successfully simulated.