CHAPTER II, SECTION 6 Each of two 10-kilowatt transmitters in combination with 37-decibel-gain parabolic antennas operating at 900 megacycles produced an effective radiated power of approximately 30 megawatts. In addition, the antenna system was designed to provide quadruple diversity reception. The random and uncorrelated received signals were combined resulting in a noise-free signal. Thusreliability of this system was based essentially upon the primary power source. A block diagram of one terminal end of the Tropo_ spheric Scatter System is included as Chart 2-19. During each test detonation, the signal from each receiver at Elmer and from an individual receiver at Nan was recorded. Neither a momen- tary nor an extended effect to path propagation was noted. VHF FM COMMERCIAL NETWORKS. The 164- to 174-megacycle commercial equipment serving TG 7.1 and TG 7.5 consisted of five repeatered networks and two simplex net- works at Bikini Atoll and three repeatered nets and three simplex nets at Eniwetok Atoll. Each network consisted of from 5 to 51 individual stations. Stations in the field included 20-watt transceivers, 20-watt mobile units, 60-watt ship- board units, and 5-watt pack sets. Remote units, controlling a common 20-watt transceiver, were used in areas where several fixed stations, close to one another, operated on the same network. Antenna installation and equipment costs were considerably reduced using this method with no degradation of service. Moreover, this ar- rangement reduced thepossibility of radio interference. Stations were located in administrative of- fices, Scientific Stations, shot barges, vehicles, and naval vessels. The 60-watt base stations were located at Buildings 204 on Nan, with antennas placed at the top of a 300-foot tower, and at REDWING Station 1518 on Elmer, with the antennas located on top of the 125-foot tower. Base station antenna systems consisted of high- gain, paired corner reflectors. In each pair, one antenna covered the atoll area and the other the ship area. On the repeatered networks an antenna multi-coupler was used with a single receiving antenna pair to feed all receivers. Individual pairs of antennas were used for each repeater net transmitter and for simplex network. Because of the basic line-of-sight limitation on VHF communications, repeatered operation was adopted to extend coverage of the larger networks and to permit intercommunications between widely scattered units in the field. At Bikini, with the advantage of a 300-foot antenna tower, it was possible for the repeater station to receive and retransmit a pack set signal from anypoint in the atoll. At Eniwetok, due to the reduced 135-foot height of the repeater antennas, Page 308 it was necessary either to increase the height of the more remote station antennas (beyond Janet), or to provide the distant field units with | a high-gain antenna with some sacrifice of mobility. Charts 2-21 and 2-22 are included to show predicted field strength contours of the Eniwetok and Bikini VHF repeatered transmitters respectively. The contours are chosen to coincide with the expected field strength in the direction of maximum antenna gain at the horizon. The distance to the horizon is contingent upon the repeater’s effective antenna height. Installation was hampered by the late arrival of equipment as a result of delayed release of funds. Also, a high percentage of the equipment was defective upon arrival as the result of factory deficiencies subsequently corrected. However, the defects were rectified, and all networks were commissioned as required and operation was satisfactory. Considerable maintenance was required to keep the units in opera- tion. No interference was experienced between the Contractor-installed networks and those installed by Edgerton, Germeshausen & Grier, working near each other and in an adjacent band. At the start of the Operation, interference was experienced on the Bikini system between individual H&N-installed nets. By the use of cavity resonators installed on the receiver in; puts and byphysical separation of the base station units, the interference was eliminated. Traffic studies were conducted during the operational period to determine the use factor of the various networks. Traffic was concentrated on a few of the circuits, with most of the circuits having very low usage. A study of parallel radio and telephone installations was made. At Eniwetok only one out of 69 fixed stations did not have an EPG system telephone. At Bikini 22 out of 88 fixed stations did not have parallel telephoneservice. VHF FM MILITARY NETWORKS. The DOD Task Unit of TG 7.1 used FM military equipment operating in the 38- to 54- megacycle band. At the peak of the DOD parti- cipation during the WAHOO and UMBRELLA events, 59 VRC-18 transceivers were in operatior in a constantly changing system of radio nets. Although repeater operation had been provided for in case of coverage difficulties, it was possible to operate all networks simplex successfully. Coverage and reliability were very satisfactory, particularly on the water shots wherefield units operated under adverse conditions. Few interference incidents were experienced. The major difficulties encountered in the installation and maintenance of these nets were the late receipt of requirements and frequent changesin criteria. In one case, it was necessary to make 14 shipboard and land installations