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Design, Construction and Operation of an Inter-City Microwave Network for the Oregon Educational Television System

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Design, Construction and Operation of an Inter-City Microwave Network for the Oregon Educational Television System AN ABSTRACT OF THE THESIS OF BENJAMIN J BALLARD for the PROFESSIONAL in ENGINEERING (Name) (Degree) (Major) Date thesis is presented June 1963 Title DESIGN, CONSTRUCTION AND OPERATION OF AN INTER-CITY MICROWAVE NETWORK FOR^THE OREGON EDUCATIONAL TELEVISION SYSTEM Redacted for privacy Abstract approved* V (Major(Mail professor) The fundamentals of microwave propagation are discussed relating to the conditions encountered in the operation of a microwave system in Western Oregon. A cost study is presented showing the price of purchasing and operating a microwave system as compared to leasing the service from a common carrier. The practical problems of installation and adjustment are pointed out along with the maintenance peculiar to the system. APPROVED: Redacted for privacy Professor of Electrical Engineering Head of Department Electrical Engineering Redacted for privacy Chairman of School Graduate Committee Redacted for privacy Dean of Graduate School Date thesis is presented June 1963 Typed by Marilyn K. Philo DESIGN, CONSTRUCTION AND OPERATION OF AN INTER-CITY MICROWAVE NETWORK FOR THE OREGON EDUCATIONAL TELEVISION SYSTEM by BENJAMIN J BALLARD A THESIS submitted to OREGON STATE UNIVERSITY in partial fulfillment of the requirements for the degree of ELECTRICAL ENGINEER June 1963 ACKNOWLEDGMENT In the preparation of this paper the writer wishes to express his thanks to Professor Louis N. Stone, Head of Electrical Engineering, for his suggestions and encouragement; to Professor Grant S. Feikert, Supervising Engineer, for the advice and help in compiling and editing information contained herein; to Professor Samuel H. Bailey, Head of News Bureau, for his help and in making photographic equipment avail able for use; and to Mrs. Marilyn Philo for her stenographic work in editing and typing this paper. TABLE OF CONTENTS Introduction 1 Basic Requirements ..... 1 Video Transmission By Lines 2 Video Transmission By Microwave 2 Engineering Design Considerations 4 Fundamentals of Microwave Propagation 4 Frequency Selection 7 Microwave Path Calculation 8 Path Attenuation 16 Equipment Requirements 13 Cost Analysis 23 Installation and Adjustment 25 Housing and Protection 25 Repeater Site . 33 Terminal Installation 34 Initial Equipment Adjustment 40 Operations 46 Capability of Network 46 Network Limitations and Reliability ........ 48 Operational Costs .... 50 Future Expansion 51 Bibliography 53 Appendix 54 Appendix I 55 Appendix II 58 Appendix III 59 Appendix IV 63 Appendix V 64 Appendix VI 65 ILLUSTRATIONS Figure Number Title Page 1 Transmission Path Calculation 9 2 Vineyard Hill to Eugene Profile Chart .... 11 3 Vineyard Hill to Prospect Hill Profile Chart . 12 4 Prospect Hill to Portland Profile Chart .... 13 5 Fresnel Zone Clearance Chart 15 6 Free Space Attenuation Graph 17 7 Map of Inter-City Microwave System ..... 26 8 Villard Hall, University of Oregon 27 9 Microwave Transmitter and Antenna at Villard Hall. 28 10 Microwave Transmitter and Antenna at the Coliseum. 29 11 The Coliseum, Oregon State University .... 30 12 Channel 7 Transmitter Building at Vineyard Hill . 31 13 Microwave Receiver and Antenna 32 14 Parabolic Antennas at Vineyard Hill ..... 35 15 Channel 7 Transmitter Console 36 16 Motorola MV-30 Microwave Equipment at Vineyard Hill 37 17 Microwave Repeater Equipment at Prospect Hill . 38 18 Microwave Repeater Site at Prospect Hill ... 39 19 Parabolic Antenna with Radome Cover 41 20 Microwave Antenna System at Portland 42 DESIGN, CONSTRUCTION AND OPERATION OF AN INTER-CITY MICROWAVE NETWORK FOR THE OREGON EDUCATIONAL TELEVISION SYSTEM INTRODUCTION When it became evident that the Federal Communications Commission had reserved television channels for educational use, the State System of Higher Education began studies to employ television in the educa tional program of Oregon. An inter-institutional committee, composed of James M. Morris, General Extension Division; D. Glenn Starlin, University of Oregon; and Grant S. Feikert, Oregon State College, was appointed by Chancellor Charles D. Byrne for this study. This commit tee submitted its report to Chancellor Byrne on July 1, 1952. The report was accepted by the State Board of Higher Education in August of 1952. Not until several years later, when funds from grants and legis lative appropriation were made available, did educational television become available in Oregon. From the onset planning had been on the basis of inter-institutional participation. BASIC REQUIREMENTS In order to develop this concept of inter-institutional partici pation, it would be necessary to connect or tie the schools together into a "network" for the common use of courses to be telecast. The requirements for transmission of video signals are quite different from methods used for audio signals. Radio has been used for a number 2 of years as a means of making available to the public as well as for in-school listening, information originating from various places throughout the state or nation. All information necessary for a standard radio broadcast is contained in the relatively narrow band of audio frequencies (30 to 7500 cycles per second). These audio signals are readily fed from one place to another over a metalic pair of wires, normally thought of as telephone lines. Video Transmission By Lines The video signal, which is standard in the industry today, occupies a band of frequencies from zero to four and one-half mega cycles per second (0 - 4.5 mc). This wide band of frequencies can not be transmitted over "regular telephone" wires without suffering serious losses. Coaxial cables, which are of special construction, are used for transmission of video signals as well as other types of high frequency signals. These coaxial cables do have some disadvantages or limitations, chief of which is the cost factor. Another limitation is the relatively high loss of signal in the line, which necessitates the frequent use of repeating amplifiers to restore signal level in long transmission lines. Video Transmission By Microwave A third method of signal transmission which has developed rapidly over the past few years is the use of the microwave band of frequencies. As the name implies, these frequencies are of very short wave length, or as is classified in the frequency spectrum 3 "super high frequency," being from 3,000 to 30,000 megacycles per second. With the development of equipment for generating and utilizing these microwave frequencies, great advancements have been made in the communications field. High on the list of uses for microwave equipment is the simultaneous transmission of video and audio signals as employed in television broadcasting. Television studios no longer need be adjacent to the television transmitter but may be located at a more convenient place. A studio-to-trans mitter microwave link can then be used for transmission of both video and audio signals from the production studio to the main television transmitter. Educational television in Oregon became a reality in the fall of 1957. At that time production studios located in the Coliseum at Oregon State University in Corvallis and in Villard Hall at University of Oregon in Eugene supplied program information to the Channel 7 transmitter located at Vineyard Hill five miles north of Corvallis. These studios were linked to the transmitter by micro wave equipment operating in the 7,000 megacycle band of frequencies. Further expansion of educational television in Oregon was realized on February 6, 1961, when KOAP-TV in Portland joined KOAC-TV in Corvallis to form the Oregon Educational Television Network. The studio and transmitter of KOAP-TV are linked with the KOAC-TV trans mitter and studio by a two-way microwave network. With the present microwave system it is possible to transmit in both directions simultaneously, with one video and two audio channels, 4 between the Corvallis and Portland studios. In addition, one video and one audio channel are transmitted from the Eugene studio to the KOAC-TV transmitter. This makes it possible for a program origi nating in any one of the three "live" studios to be broadcast on either or both Channel 7 or Channel 10 transmitters, or to be video tape recorded at either the Corvallis or the Portland studios. ENGINEERING DESIGN CONSIDERATIONS Microwave relay systems utilize a transmission path which is only partially controllable by the user or installer of the equipment. Thus the performance and the reliability of the system will depend not only upon the equipment, but upon the quality of the path over which it must operate. It is necessary therefore, for careful planning to be given to the microwave system prior to installation. It is in this planning that the engineer assumes the major role in determining requirements based upon terrain conditions, meteorological effects, and the microwave principles. Fundamentals of Microwave Propagation It is popularly assumed that the microwave energy travels in a "beam" from the transmitter antenna to the receiver antenna, similar to a beam of light produced by a searchlight. Since both light waves and microwaves are forms of electromagnetic radiant energy, it follows 5 they both are subject to the same laws and display similar character istics. The analogous properties includes a. Obstruction or attenuation of the energy by solid objects such as hills, buildings, trees, etc. b. Reflections from flat surfaces such as sides of buildings, smooth terrain, water, and layers of still air. c. Diffraction around edges of solid objects. d. Refraction, or bending by the atmosphere. Line of Sight. In order to assure reliable operation of a micro wave system, special considerations must be given to path selection with regard to the forementioned properties. "Line of sight" or optical clearance over a microwave path is not satisfactory. It is necessary to have what is called Fresnel Zone clearance. If antennas are properly aligned, the region in which the useful radiated energy is concentrated, is in the center of the beam radiated by the trans mitting antenna. Within this beam is a region called the first Fresnel Zone.
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