MIL-HDBK-416 1977 Edition, November 15, 1977
LINE OF SIGHT,MICROWAVE COMMUN.SYS.(HANDBOOK)
Includes all amendments and changes through Cancellation Notice 1, July 15, 1999
Additional Comments: CNCL NO S/S
This handbook for line-of-site (LOS) radio systems include techniques and procedures necessary for communications engineers to design system utilizing state-of-the-art principles existing now. Information in this handbook is applicable to systems operating at frequencies between approximately 1 to 40 GHz, and outline the design methods to be employed in the engineering of LOS facilities so that they will operate in accordance with the required criteria. In order for an actual system to meet Defence Communication Agency (DCA) standards and objectives, the appropriate and current Military Standards (section 2.1), DCA circulars, CCIR Recommendations or service-wide publications (section 2.2) must be consulted as source documents for performance criteria. The referenced standards are updated as the state of the art improves, and such improved performance standards are not necessarily reflected in the examples given in this handbook.
The handbook categorized the basic information which must be supplied to, or assumed by, the engineer before he can determine system feasibility and start the design procedures.
Information is provided first on how to start the design work with a preliminary selection of sites and routes based on stated performance requirements. Selection is aided by obtaining preliminary path profiles and calculating initial transmission loss values.
Procedures are then established for planning and performing field surveys and using the results obtained for further establishing site and route preference.
Worksheets and procedures are presented for the detailed evaluation of individual links after provision is made for adequate terrain clearance. Various equipment alternatives are discussed and quantitative data for equipment planning are supplied.
Atreatment of overall system planning is presented under the basic topics of system layout, frequency allocation, intra-system interference allowable link noise quota, and performance predictions.
This handbook is intended to assist suitably qualified personnel in designing microwave systems to current state-of-the-art standards, but cannot be considered a substitute for experience and education in the engineering of such systems.
Various aspects of design problems are considered and several alternatives to their solution are presented wherever possible. Although the handbook draws information and ideas from many sources, it is not to be used exclusively. Serious or special problems may require that other applicable sources of information be consulted.
The handbook applies to microwave line-of-sight (LOS) radio systems which are used to provide multichannel communication between fixed locations. Such point-to-point systems generally use a carrier frequency in the range of 1 to 40 GHZ over paths typically from 10 to 100 km long. Antenna heights above ground are usually adequate to provide line-of-sight paths under most circumstances, but seldom exceed 100 m. In some cases, passive reflectors are employed to obtain line-of-sight conditions.
Individual paths or links are integrated into a system which may, through the use of repeaters, extend over various types of terrain for a distance of several hundred kilometers. The transmitters are normally low power, from 0.1 to 10 W, and with companion receivers share the use of high-gain directional parabolic antennas between 1 and 5 m in diameter, or various types of horns having equivalent gain and beamwidth characteristics. These systems provide the transmission means for communication traffic consisting of voice, teletype, facsimile, digital data, and of visual displays.
The microwave carrier must be modulated by many information streams which are separated by multiplexing processes. Primarily two basic kinds of multiplexing are used on microwave LOS links, namely frequency division multiplex and time division multiplex. Frequency division multiplex (FDM) keeps the information streams separated using frequency division by means of bandpass filters. Time division multiplexing (TDM) uses logic circuits to isolate the channels from each other in time.
The main objective of this handbook is to provide methods for microwave LOS link and system design. Major topic areas discussed are: obtaining detailed path profiles, path loss calculations, service probability and fading range estimates, radio interference investigations, adherence to DCA noise standards, and link equipment requirements. Graphs, basic equations, and tables are provided for optimizing the design through the use of trade-off studies in order to insure that the functional, reliability, and safety requirements are met. Most of the design procedures and engineering analyses can be performed using a slide rule; more accurate calculation procedures are required for great circle calculations.
Certain analyses are performed to insure the compatibility of the individual links with the total communication system objectives. These are mainly (1) system performance predictions based on the composite characteristics of the individual links, (2) the compatibility analyses of the individual frequency assignments within the band, and (3) the specification of branch and terminal requirements so that the linking of branches at the sites is achieved properly.
This handbook may be used to provide (1) a chronological order of procedures for designing the system, and (2) information on specific topics which may appear as particular design problems.
The organizational block diagrams (section 1.6) should be used as an aid in defining a chronological order of procedures. They show the sequence of design tasks and indicate required information or assumptions for each major step.
For information on specific topics, the table of contents and the index should be consulted. Many topics are considered from several points of view or at different stages in the design and, therefore, are discussed at more than one place in the handbook. The technical description contained in Chapter 6 or in worksheets provided are needed for some of the technical processes. Examples of the worksheets may appear in the text, and blank worksheets are included in Chapter 6.
The main body of the handbook (Chapter 4) is organized as shown in the following block diagrams (figures 1-1 to 1-5). They indicate that subject matters are discussed in the handbook as they would most probably occur chronologically in actual system design. If the reader has knowledge of where in LOS system design a problem is to be considered, he may view the diagrams and acquaint himself with specific or related tasks for a further understanding of that particular problem.
Major topics are numbered using periods to separate sections and subsections. These numbered topics appear in the table of contents. Each paragraph in the following chapters is individually numbered.
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