• A-M/AGC Weighted Pre-Detection Diversity Combining

      Hill, E. R.; Pacific Missile Test Center (International Foundation for Telemetering, 1977-10)
      A method has been proposed for improving the performance of automatic gain control (agc) weighted diversity combiners in the presence of fast fading radiofrequency (rf) signals by use of the amplitude modulation (a-m)(detected linear intermediate-frequency (i-f) envelope) in addition to the agc voltage to weight the combiner. Also suggested was a method for selecting the channel with the best signal-tonoise ratio (SNR) by use of the a-m and agc voltages. Experimental hardware has been constructed for evaluation of three configurations: an a-m/agc weighted combiner; an a-m/agc based selector; and an a-m/agc combiner/selector where the criterion for combine or select is determined by the phase error between the two channels. An experimental study was also conducted of the phase-locked loop (PLL) to determine the best configuration and parameter values for the combiner application (where relatively large phase errors are permissible). Data were taken under laboratory and operational (Vandenberg Air Force Base) conditions and are compared with data taken with a commercial agc weighted combiner.
    • Experimental Comparison of Pulse Code Modulation Codes for Magnetic Recording

      Law, E. L.; Pacific Missile Test Center (International Foundation for Telemetering, 1977-10)
      The bit error probability (BEP) versus signal-to-noise ratio (SNR) was experimentally determined for Non-Return-to-Zero-Level (NRZ-L), Bi-Phase-Level (BIΦ/-L), Delay Modulation (DM) and Miller Squared (M²) codes for a bandpass channel. This was done by passing the data through a 400 Hz to 500 kHz Bessel bandpass filter and linearly adding noise. The power spectral density of the noise was shaped to match the noise out of an analog magnetic tape recorder running at 30 inches per second (in./s). This provided a simulation of an optimum wideband 2.0 MHz tape recorder running at 30 in./s (no flutter, tape dropouts, etc.). The bit rate, pattern, and code to be tested were then selected. The SNR was varied until the bit error probability was approximately 10⁻⁶ With a commercial Pulse Code Modulation (PCM) bit synchronizer with a "good" dc restorer and a pseudo-random pattern at 1.0 megabits per second (Mb/s) (33.3 kilobits per inch (kb/in.) equivalent packing density), NRZ-L had a 4 dB SNR advantage over DM and a 14 dB advantage over BIΦ/-L for a BEP of 10⁻⁶ through the bandpass channel. At 1.5 Mb/s, NRZL had a 6 dB advantage over DM and a 10⁻⁶ BEP was not achievable with BIΦ/-L coding. For a synchronizer with no dc restoration NRZ-L had only a 1 dB advantage over DM at 1.0 Mb/s and also only a 1 dB advantage at 1.5 Mb/s. M² gave the same results as DM for pseudo-random data. However, M² was relatively insensitive to patterns while DM and NRZ-L required a higher SNR with a "good" dc restorer and lost synchronization completely with no dc restorer for worst case 16-bit repeating patterns.
    • Review of Microstrip Antenna Development at the Pacific Missile Test Center

      Kaloi, C.; Pacific Missile Test Center (International Foundation for Telemetering, 1977-10)
      Pacific Missile Test Center personnel have been conducting theoretical and experimental studies on microstrip antennas since 1965. A number of operational microstrip antenna systems have been developed. This report reviews development efforts at Pacific Missile Test Center on types of microstrip antenna elements used in these operational systems. Results of near field probing of different microstrip antenna elements are presented. These results are used as a basis to discuss microstrip antenna electrical characteristics such as orthogonal current oscillation, orthogonal charge oscillation, dipole moment of charge distribution oscillation, dipole moment of charge distribution rotation, far field radiation patterns, polarization, etc. Application of microstrip arraying techniques on thin flexible substrates that can be readily mounted conformally to the exterior surface of a missile without missile disassembly is discussed.