No abstract
A method for networking a small number of serial HF modems has been developed at Harris. The objective of this particular technique is to provide an extremely robust method for communicating low rate data at differing priorities over the HF band. Automated frequency selection is incorporated without requiring additional sounding equipment. A signaling scheme with capabilities similar to the one employed by Harris' serial HF modems is required by this network approach.This paper discusses a simulation of the network. The simulation runs on Harris' Concert system utilizing up to 64 parallel processors. It simulates the HF channel, modem and networking protocols as well as generation and queueing of traffic. Use of parallel processors allows the simulation to be partitioned in a fashion that closely parallels an implementable system. Emphasis will be placed on requirements for meaningful simulation of the HF channel, as a description of the network and its performance has been previously reported.' INTRODUCTION This paper describes simulation work performed on a HarrisStressed Communication IR&D initiated during January of 1984. The goal of this task was to develop a simulation that could demonstrate and evaluate various networking techniques involving terminals equipped with Harris' serial HF modems. The network concept for this simulation was a small number of terminals in a network where the average data rate is quite low.A secondary objective of this project was to evaluate our Concert parallel processing testbed (being developed concurrently on a different IR&D project) as a simulation machine. Many characteristics of the resulting program, such as the choice of the C language, were consequences of this second objective.
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This paper discusses the design considerations In volved In the development of a ruggedlzed 50-watt rf power amplifier, tunable over the frequency band of 215 to 245 megacycles* The amplification Is accomplished In one stage, using an Eimac ceramic tetrode. The unit Is capable of operating under severe airborne environmental conditions. Several novel features are Incorporated In the amplifier design to match the circuitry to the ceramic tetrode. These features Include a tuned Input tank com posed of two transmission lines, and a tuned transmissionline output tank that has been curved to conserve space. The unit Is blower cooled and requires approximately 100 cubic Inches of housing volume In Its present configuration. GeneralIn the design of an rf telemetry link, one of the major considerations Is the maximum reliable range over which the telemetry system can operate. A complete analysis of this design criterion is given In a paper presented by Mr. Scharla-NIelsen before the National Telemetry Conference In 1956. However, It will suffice to say that the reliable operating range of any given type of telemetry system over any given atmospheric path Is determined by three factors. These are: (1) the transmitted power, (2) the gains of the transmitting and receiving antennas and (3) the receiver sensitivity.For many applications, the last two factors are pre determined, usually by the state of the art in receiver design and the minimum allowable beamwidth of the an tennas. In stich cases, the only method available for in creasing the maximum reliable range Is to Increase the transmitted power. Recognizing this situation, Radiation, Inc. has designed and tested an rf power amplifier capable of delivering 50 watts to a 50-ohm load, Figure 1 . Design ProblemsSince the unit Is to be used In airborne applications, the prime design criteria were: (1) maximum ruggedness, (2) minimum size, and (3) maximum efficiency. The final design configuration that realized these objectives Is somewhat novel.In addition to the major design objectives, the unit was designed to meet the following specifications:(1) The amplifier must supply 50 watts to a 50-ohm Figure 1 load when driven from a two-watt, 50-ohm rf transmitter.(2) The amplifier must be tunable over the frequency range of 215 mc to 245 mc.(3) The required power gain of 25 must be accom plished In one stage to be'consistent with the re quirement of minimum size.Since environmental considerations were of utmost Importance, the first problem was to select a suitable tube. The final choice was a 4CX300A Eimac stackedceramlc tetrode. The tube Is a high-gain, high-power tetrode with excellent environmental qualifications. However, electrically It presented some major problems.Most severe was the fact that the tube combined with its socket has an input capacitance in the vicinity of 40 micro-microfarads. To operate the tube efficiently, It was desired to use class-C operation, or as close to class-C operation as could be obtained. The driving voltage, however, was being supplied fro...
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