SUBCOURSE EDITION MM0750 0 HIGH-FREQUENCY FIXED-STATION RADIO SYSTEMS VALIDATION INFORMATION This subcourse has been validated in the field by continuous use for over 3 years. i SUBCOURSE 750 Contents Page Credit Hours Introduction 1 Lesson 1 - Introduction to High-Frequency Communications Systems 3 2 Lesson 2 - Communication Circuit Quality 29 2 Lesson 3 - Transmitting Equipment 57 2 Lesson 4 - Receiving Equipment 90 2 Lesson 5 - Antenna Systems 111 2 Lesson 6 - Mobile Radio Stations 148 2 Lesson 7 - Frequency Planning 169 2 Lesson Solutions Lesson 1 192 Lesson 2 194 Lesson 3 195 Lesson 4 196 Lesson 5 197 Lesson 6 199 Lesson 7 200 Examination 202 2 Total Credits 16 * * * IMPORTANT NOTICE * * * THE PASSING SCORE FOR ALL ACCP MATERIAL IS NOW 70%. PLEASE DISREGARD ALL REFERENCES TO THE 75% REQUIREMENT. ii SUBCOURSE 750 HIGH-FREQUENCY FIXED-STATION RADIO SYSTEMS INTRODUCTION To maintain efficient and effective fighting forces, a large volume of logistical and administrative data must be exchanged among the various command headquarters throughout the world. The Defense Communications System is a worldwide point-to-point communications network designed for operations on a global scale. It provides data, teletypewriter, voice, and facsimile facilities. It is a system of interconnected fixed radio stations and leased or allocated long-distance wire channels. The system does not include local tactical and special-purpose communications circuits, but its facilities are available for use by all echelons of the Army, and long-distance circuits may be permanently or temporarily allocated to any approved user. Although the Defense Communications System is controlled by the Department of Defense, portions of the system are operated by the three military departments. The Army portion is operated by the US Army Communications Command, one of the major commands of the US Army. The purpose of this subcourse is to familiarize you with the principles involved in long-distance radio systems, the problems associated with establishing and maintaining these systems, the operational equipment used, and the duties of those individuals responsible for them. This subcourse consists of seven lessons and an examination, as follows: Lesson 1. Introduction to High-Frequency Radio Communications Systems Lesson 2. Communications Circuit Quality 1 Lesson 3. Transmitting Equipment Lesson 4. Receiving Equipment Lesson 5. Antenna Systems Lesson 6. Mobile Radio Stations Lesson 7. Frequency Planning Examination Credit Hours: 16 You are urged to finish this subcourse without delay; however, there is no specific limitation on the time you may spend on any lesson or on the examination. Texts and materials furnished: Subcourse Booklet, which you may keep, and Examination. 2 LESSON 1 INTRODUCTION TO HIGH-FREQUENCY RADIO COMMUNICATIONS SYSTEMS TRAINING OBJECTIVE: Action: Be able to list the functions of Defense Communications System and fixed station radio systems. Conditions: Given SSO 750. CREDIT HOURS: 2 LESSON OBJECTIVES When you have completed this lesson, you should know that: 1. The Defense Communications System is a global communications network operated by the Army, Navy and Air Force, but controlled by the Defense Communications Agency. 2. The use of single-sideband in high-frequency fixed-station makes possible the reduction of channel width and increases the efficiency of power utilization. 3. A single-sideband signal has better signal-to-noise ratio than a double-sideband signal because the receiver bandwidth may be reduced from the normal bandwidth required. 4. Physical separation of transmitter and receiver sites in a high-frequency long-distance radio station is required to minimize interference. 3 ATTACHED MEMORANDUM 1-1. DEFENSE COMMUNICATIONS SYSTEM. a. Control by Defense Communications Agency. The communications system by which every theater and separate command maintains a contact with the Joint Chiefs of Staff is known as the Defense Communications System (DCS). This network, permanently established and permanently operating, is controlled by the Defense Communications Agency (DCA). It consists of radio circuits installed, operated, and maintained by the military departments; government-owned cables; and leased commercial cables and long-distance wire and radio circuits in the United States and overseas. The DCA controls the system through a series of communications control centers, and provides a means of integrating the communications systems formerly operated independently by the military departments. b. A Worldwide System. The network is a global communications system that provides electrical communications facilities (teletypewriter, voice, data, facsimile, etc.) between military activities throughout the world. In addition, the system provides reliable communications for the Department of Defense, Presidential communications support, and various government agencies. c. Deployment of Stations. The need for a communications station in any part of the world depends on the interest of a particular military service in that part of the world. For example, consider Hawaii as a typical example of representation by all services -- Aliamanu represents the Army, Wahiawa represents the Navy, and Hickam AFB represents the Air Force. In figure 1-1, these three military services are shown as the HON (Honolulu) subcomplex. And so it is throughout the world. Each oval in figure 1-1 represents one or more services, and each line represents the total system from one subcomplex to another. Thus, figure 1-1 represents the DCS, a giant system that can provide communications in peace or in war. Figure 1-1. The Defense Communications System Complex. (Located at back of subcourse booklet.) 4 d. Station Characteristics. Most radio stations in the DCS used for long-distance communications are rather large. Normally, large amounts of bulky equipment items are grouped together in a selected area for reasons of security, availability of power, and for efficiency of operation and maintenance. Moreover, since the antennas are in the high-frequency range, they cover large amounts of real estate. The combination of these characteristics dictates that the stations be emplaced in one location for long periods of time. Stations so emplaced are called fixed stations. However, mobile versions of these stations have been developed and may be transported to trouble spots around the world. In spite of differences in size and physical appearances, mobile and fixed stations must have compatibility of signal characteristics. Functionally, the equipments in these stations are designed for long-distance communications in the high-frequency range, and are variously known as long-haul and long-range. e. Long-Haul Facilities. The facilities of the DCS consist of long-haul point-to-point radio, wire, and cable circuits used with diversified equipment, such as single-sideband (SSB), electronic time- division-multiplex, automatic and semiautomatic teletypewriter relay, and high-speed data terminals. f. Major Links. Long-distance radio facilities furnish the major links or trunkline circuits between the stations in the DCS. Occasionally, short-distance radio facilities similar to those used for keying lines may be used to connect an outlying terminal station to its servicing relay station. g. Circuit Assignments. Responsibility for providing communications facilities in a given area is assigned by DCA to the Army, Navy, or Air Force. Circuit assignments for traffic flow are designated by the DCS out of the facilities furnished by the selected service. The selected service also provides the personnel and command structure to implement the operation. The Army portion of the DCS is operated by the US Army Communications Command (USACC). The major traffic arteries of the DCS are shown in figure 1-1. h. Full-Duplex Operation. Each of the DCS long-distance radio circuits includes two complete radio stations, one at each end of the circuit. The stations normally operate on a full-duplex basis and require an assigned radio frequency for each direction of transmission. The radio stations usually operate in space diversity; that is, two antennas are required to receive the radio signal. The arrangement is shown in block form in figure 1-2. 5 Figure 1-2. A full-duplex fixed radio station communication system. i. Questions. 1-1a. What governmental agency is charged with controlling the Defense Communications System (DCS)? a. Department of State. b. Defense Communications Agency. c. National Communications System. d. Federal Communications Commission. 6 1-1b. The Army portion of the DCS is operated by the a. US Army Electronics Command. b. Defense Communications Agency. c. US Army Satellite Communications Agency. d. US Army Strategic Communications Command. 1-2. ORGANIZATION OF A FIXED RADIO STATION. A military fixed radio station often is divided into three separate installations: a tape relay center combined with technical control at the terminal station, a radio transmitter station, and a radio receiver station (fig 1-3). Physical separation of the transmitter and the receiver sites is required to minimize interference. Figure 1-3. Organization of a fixed radio station. 7 a. Tape Relay and Associated Technical Control Center. For efficient operation, the technical control center usually is located adjacent to the tape relay station. It is desirable that both of them be located in the same building and separated by a glass panel so that operators in the technical control center can oversee the operations