INTRODUCTION

The final section of this manual introduces the related manuals that treat the specialized technical phases of the systems which comprise the AN/FSQ-7 Combat Direction Central and the AN/FSQ-8 Combat Control Central.

The final chapter lists and describes the various technical manuals in this series, and provides a brief description of several sources of supplementary reference material which will aid in further study of the AN/FSQ-7 and AN/FSQ-8.

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Simultaneously, studies were made on the combined use of digital computers and radar-data transmission equipment for application to air defense. The testing of a high-speed digital computer was recommended to the Air Force to provide information on the capabilities of such equipment to solve the ever-growing problem of air defense. The findings of this program led to many new concepts for solving the problem and resulted in the establishment of an experimental project which gave rise to the SAGE System. This project was developed is three major phases: the 1953 Cape Cod System, the 1954 Cape Cod System, and the experimental SAGE subsector.

The experimental SAGE Subsector provides experimental data on electronic reliability, computer pro grams, and operating procedures. It is organized to sup. port the regular functions of a Direction Center and is used to obtain operational approval and to determine required equipment modifications.

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Staff to the Continental Air Defense Command (CONAD). The primary concern of CONAD is the protection of retaliatory forces, population, natural resources, and industrial potential during initial or sustained attacks by hostile forces. This defense must ensure successful counterattack by this country and must also ensure the eventual successful conclusion of hostilities.

To carry out its assigned tasks, CONAD delegated certain portions of the air defense mission to subordinate echelons. This delegation has geographical as well as operational applications.

The Continental Air Defense Command is presently organized into three Defense Forces, and this structure is reflected in the SAGE System. Each Air Defense Force is composed of a number of Air Defense Divisions. The Air Defense Division is relieved of direct supervision of groups and squadrons. However, its area of responsibility is large, making mandatory the minimizing of administrative and logistic responsibilities at this level. These responsibilities are delegated to the Air Defense Wing.

The area for which an Air Defense Division is responsible is normally composed of three or more sectors. The headquarters for the division is the Combat Control Center. The Air Defense Division exercises operational control of units designated for air defense operations within the division and is the level at which coordination with adjacent divisions is achieved.

The Air Defense Wing, with headquarters at the Combat Direction Center, has subordinate units that are primarily weapons and radars. The area of responsibility of the Air Defense Wing is called a sector. To perform the functions of air surveillance, identification, and weapons control, detailed information on all defense elements is continually maintained.

1. The facilities required to process and transmit air surveillance data from data-gathering sources to Combat Direction Centers.
2. Combat Direction Centers, where air surveillance data is processed, evaluated, and developed into air situations at a sector level from which threat evaluation, weapons assignment, and appropriate weapons guidance orders are generated.
3. The facilities required to transmit situation data from Combat Direction Centers to Combat Control Centers and other Combat Direction Centers.
4. Combat Control Centers, where situation data from the Combat Direction Centers is processed, and from which the utilization of weapons resources can be monitored and directed.
5. The facilities required to transmit instructions from Control Centers to Direction Centers and to forward divisional situation data to other Control Centers and higher echelons of command.

An important characteristic of the SAGE System is its flexibility to accept improvements in radar techniques and equipment as they evolve. The AN/FSQ-7 and the radar-data transmission equipments greatly reduce the time delays inherent in data processing and permit more effective use of data from many radars. Therefore, a large number of gap-filler radars can be used to provide an integrated, overall air picture.

Each Direction Center controls, and is connected with, all air defense radars that are geographically

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located within the sector. These radars provide adequate radar coverage. The air situation picture for the entire United States, therefore, is continuously maintained by both a perimeter radar screen and a radar umbrella. Any aircraft entering or originating in the United States can be detected and tracked continuously.

Aircraft equipped with Mark X equipment identify themselves automatically and do not require further action for identification by components of the SAGE System.

The MCIS requires all aircraft entering the coastal areas of the United States to identify themselves by means of prearranged check words and check maneuvers, as well as to use only predesignated corridors in approaching the Air defense Identification Zone (ADIZ)

Flight plans are required of all military and commercial flights. These flight plans are inserted into the AN/FSQ-7 computers and are matched with radar returns, continuously and automatically, to aid in identifying the spotted aircraft. Computer programs record the number of times an aircraft deviates from its assigned course and notify appropriate personnel each time a deviation occurs.

The air bases under the control of a Direction Center keep the center informed of their operational status, and computer programming indicates the number of weapons committed during any action. In this fashion, personnel at the center are kept up to date on the status of weapons available for assignment to targets.

Scrambled interceptors are given mid-course guidance by the computer and are aided in their return to base by computer-generated directions. Provisions are

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The Control Center is equipped with an AN/FSQ-8 Combat Control Central. This equipment is basically the same as the AN/FSQ-7 Combat Direction Central, differing primarily to the extent that some of the input and output equipment is eliminated in the AN/FSQ-8, since it receives no raw radar data. Also, fewer display and drum facilities arc required at the Control Center. The function of the Control Center in solving the air defense problem is to combine, summarize, and display the air battle picture for the supervision of the several sectors within the division. (See fig. 2-3.) The major activities with which the Combat Control Center is concerned are:

1. Evaluation of the nature, strength, and direction of the threat
2. Supervision of the air battle
3. Allocation of weapons to the sector, deployment of weapons, and use of augmentation forces
4. Co-ordination with adjacent Control Centers
5. Ordering conditions of alert for the division
6. Ordering overall status for weapons in each sector
7. Manual plotting of distant early-warning information
8. Dissemination of defense warnings to civilian and military agencies
9. Implementation of Security Control of Air Traffic (SCAT) and Control of Electromagnetic Radiations (CONELRAD) plans
10. Forward air situation and status of the division to higher echelons of command

At the same time that each Direction Center in the division develops and displays its own picture of the air battle in its particular sector, the data is automatically forwarded to the Control Center. At the Control Center, the air situation for each sector is displayed both separately and cumulatively. In other words, the Control Center maintains displays of the air situation in each individual sector within the division and, at the same time, combines the several sector air situation pictures to present an overall picture for the entire division. Any change in the air situations of the sectors is reflected immediately on the displays devoted to the individual sectors. These changes also immediately alter the overall air situation picture for the entire division. Thus, personnel at the Control Center are provided with an up-to-the-minute picture of the air situation in the area for which they are responsible (fig. 2-4).

They are in the most advantageous position to observe developments, make decisions, and issue commands which will be most effective in neutralizing the threat. Should the air threat move into an adjacent area, the adjacent Control Center may be forewarned in time to meet the threat. In receiving the forewarning, the adjacent Control Center receives all pertinent data concerning the air situation with which it is apt to be faced. At the same time, this data is forwarded to the next higher echelon of command, which supervises the activities of the several divisions so that the air situation, on a regional level, may be summarized and kept up to date.

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The process of air defense may be broken down into a series of related functions such as detection, identification, tracking, weapons control, etc. To perform these functions efficiently, the AN/FSQ-7 Combat Direction Central is capable of assembling large quantities of diverse information from many sources. This information includes radar data, commercial and military aircraft flight plans, and weather data. The Viral f is also capable of processing data to identify and track all aircraft, friend or foe. The AN/FSQ-7 also directs antiaircraft batteries-,and all interceptors, manned or remote-controlled; to positions close enough to the target for the interceptor itself to complete the interception. In addition, the AN/FSQ-7 keeps all personnel fully informed about the air situation, alerts them to actions required, displays possible recourses for action, and continually computes and displays all subsequent changes to the original data.

The functions of the Control Central are largely supervisory in nature. Personnel at this echelon of command are responsible (1) for monitoring the action in each of the sectors comprising the division and (2) for making decisions relating to the allocation of weapons. In addition, personnel at the Control Central are responsible for co-ordination with other Control Centrals and for presenting the divisional air situation to higher echelons of command.

The first five systems listed above are integral part: of the data-processing operations of the AN/FSQ-7 and the AN/FSQ-8 and execute functions within themselves which contribute to the overall operational solution of the air defense problem. The two latter systems listed above are not directly concerned with the defense functions of either Central.

For purposes of uniformity in design, production and maintenance, the AN/FSQ-8 equipment installed at the Control Center is almost identical to its counterpart the AN/FSQ-7 at the Direction Center. However, because of functional differences, certain portions of the equipment at the Control Center are either made inoperative or entirely omitted.

The Combat Control Central requires fewer operating personnel and has fewer display consoles than the Combat Direction Central. The Combat Control Central does not process raw radar data; therefore, the equipment required for receiving and processing radar data is unnecessary at these installations. Likewise, the amount of manual data input equipment is reduced. It follows logically that the computing capacity of the AN/FSQ-8 will not be as heavily committed as that of the AN/FSQ-7. Therefore, the Combat Control Central is able to assume additional activities in the future as the needs arise.

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The discussion of the various systems in this manual is brief, general, and designed merely to acquaint the reader with the overall functions of the systems. For a complete detailed discussion of the various systems, the reader is directed to the related manuals devoted specifically to the various systems. These manuals are identified in Chapter 5.

The Input System comprises four elements (fig. 3.2), which are named for the types of input data they process:

Input data to the AN/FSQ-7 is transmitted automatically, from radar equipment. XTL information from other Centers is also sent automatically. Certain air surveillance, status, and other data received sporadically or at an extremely slow rate can be inserted manually into the machine. This slow-changing data is received at the Direction Center by voice telephone or by manually operated teletype equipment, processed by MDI operators, and inserted into the AN/FSQ-7 through card machines.

A radar-mapping technique employing a plan position indicator (PPI), a mask, and a photocell removes areas of unwanted data, such as ground clutter, from the system. A mapper console displays all radar returns on a PPI presentation, allowing an operator to evaluate the target indications and to eliminate those that are undesirable.

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The LRI drum stores FGD, Mark X, and heightfinder messages until the computer is ready to use them.

In the strict sense of the word, the term crosstell refers only to the exchange of information between Centrals of equal command; i.e., between AN/FSQ-7 Combat Direction Centrals or between AN/FSQ-8 Combat Control Centrals. The XTL element of the Input System in the Combat Control Central, however, also receives information from the subordinate Combat Direction Centrals. This operation (from Direction Central to Control Central) is called forwardtelling and is distinguished from crosstelling. However, since both crosstold messages from other Control Centrals and forwardtold messages from Direction Centrals are accepted by the XTL element of the Control Central, both are considered to be the same for purposes of discussion in this chapter.

The overall function of the MDI element is to process input data which is manually introduced into the machine. This data includes four general categories of information:

• information entered on IBM punched cards and read into the MDI element by means of computer entry punches;
• track data appearing on display scopes, picked up by a manually operated light gun, and fed back into the MDI element;
• messages initiated by operation of intervention switches;
• and status signals to the Central Computer, indicating the active or standby status of certain elements and channels.

To process these various inputs, the MDI element is divided into two sections, each with its own particular functions. These two sections are the drum entry section and the direct entry section. Due to the disparity in the speeds of assembling messages, each of the two sections processes data originating from different sources.

The test pattern generator is capable of being operated either by manual control alone or by both manual control and computer control together. Messages can be initiated, terminated, or continuously repeated under either manual or manual-computer control. During certain operations, the TPG is under complete manual control, the messages being composed, initiated, and terminated by manually set switches. During certain other operations, the messages are composed manually but are initiated by instructional pulses sent out by the Central Computer.

********* pages 15 and 16 were recovered from microfilm, and a bit noisey ********

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As an auxiliary memory, the Drum System can store information indefinitely. The drums performing this function are accessible only to the Central Computer System, since the other systems have no need of auxiliary storage facilities. Computer programs, subprograms, tables of reference data, etc., are the types of data most generally stored on the auxiliary drums.

Central Computer System programs and subprograms, for the most part, are too extensive to be stored entirely in the memory of the Central Computer System; therefore, additional storage space is provided in the Drum System. The access time of data stored on drums, while slower than the access time of data stored in computer memory, is appreciably faster than the access time of data stored on card and tape machines. The drums, therefore, fulfill the requirements of storage capacity at a medium access time.

The Central Computer is capable of adding, subtracting, multiplying, and dividing. More complicated operations such as extracting square roots and evaluating complex variables can be performed by combining the basic arithmetic operations. The computer is designed to respond to simple stereotype instructions, each of which causes the computer to perform a single arithmetic operation. An extended sequence of such instructions, resulting in the solution to a problem, is called a program.

When solving any given problem, the Central Computer actually uses only the addition process, reducing all other processes to types of addition. This is more easily accomplished in a computer by utilizing the binary rather than the decimal number system. The binary system is based on a 1 or 0 (yes or no) principle and, consequently, requires circuits with two stable conditions to indicate a 1 or a 0. The decimal system, involving 10 digits (0 to 9) would require circuits with 10 stable conditions.

The function of the Central Computer System is to process algebraically and logically the military tactical data supplied to it by the Input System via the Drum System, transferring the results back to the Drum System for subsequent distribution to the Display and Output Systems.

In addition to processing data, the Central Computer System operates as the main control for the Central. As data is being processed, the Central Computer generates signals, as instructed, and sends them to the Drum System for utilization by the Input, Display, and Output Systems. These signals control the flow of data between systems, initiate operational cycles, set up control circuits for the coming operations and, in general. synchronize the actions of each system with those of the Central Computer System.

Functionally, the Central Computer System is divided into seven groups:
a. Instruction control element
b. Selection control element
c. Program control element
d. Arithmetic element
e. Internal storage devices
f. Associated IO units
g. Manual controls and computer indicators

The instruction, selection, and program control elements sequence, co-ordinate, and control all processes in or allied with the operation of the computer. The entire instruction control element and a part of the program control element govern internal computer operations, while the selection control element and the remaining part of the program control element govern external computer operations primarily connected with 10 devices.

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The arithmetic element performs arithmetic processes using numerical data as instructed by the program. The associated 10 units are commercial IBM machines modified for use with the computer and are not to be confused with the Input and Output Systems of the Central. The manual control facilities enable personnel to start, operate, shut down, and service the computer.

The selection control element synchronizes, controls, and directs data being transferred between the computer memory element and the several IO units including the Drum System. Prepared instructions, set ting up control circuits in the selection control element must be performed in advance of the actual transfer of information. This enables the information transfer t< be properly initiated and processed.

The selection control element also incorporate: circuits which permit the Central Computer, directed by a specific program, to perform certain operations affecting the electromechanical units allied with the 10 units and the several other electromechanical units in the system. In addition, the selection control element determines existing conditions in the Central and directs the operations of the computer accordingly.

The program control element, in order to procure specific instructions, controls the selection of internal storage devices and such information as may be required by an instruction. In addition, the program element sequences the transfer of each instruction stepped out of the internal storage devices at the proper moment.

In guiding the processing of information, the program element co-operates with other elements of the computer. The instruction control and program elements together sequence and control the internal information-processing operations. The program and selection control elements together co-ordinate and effect the external transfer of information between the computer and other systems of the Central. The program element, therefore, contains circuits associated both with the internal control operations of the instruction control element and with the external control operations of the selection control element.

Primarily, the arithmetic element employs the four basic arithmetic operations (addition, subtraction, multiplication, division) in the performance of its functions. Operands for the calculating processes are obtained from the computer memory element. The setting up of arithmetic operations is governed by add-class and multiply-class instructions which provide command pulses from the instruction control element. The result of the calculations is either retained in the arithmetic element for further processing or transferred to the memory element for storage until required by a subsequent program.

There are two core memory elements contained in the computer. These elements are high-speed storage devices that are able to store and facilitate rapid access to thousands of binary words. Each of the core memory elements is divided into three units: a left memory unit. a core memory array unit, and a right memory unit. Both memory units are composed of equipment associated with the transfer of information between the core memory elements and other systems as well as the computer itself. The core memory units are composed of actual arrays of ferrite cores in which information is stored.

The test memory is composed of 19 registers and other equipment associated with the transfer of information between the test memory and the computer Physically, certain portions of the test memory are located in two separate units. The plugboard control panel and the control switches are located on the duplex maintenance console, and the addressing and readout control circuits are located in the left arithmetic unit.

An input device associated with the computer may be defined as a unit which transmits data directly into the computer. An output device is a unit which receive data directly from the computer. Certain units, because of the nature of their functions, may be considered a; being both input and output devices. The Input System and the Output System do not deal directly with the computer, as the data for these Systems must first pass through the Drum System.

The duplex maintenance console contains the majority of the controls and indicators for the manual operation of the Central Computer System. The alarm and neon indicators on the console show the status of the computer, and virtually all manual program and checking operations are affected by means of the con sole controls.

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The duplex switching console is used by maintenance personnel to establish the status, active or standby, of the separate sets of duplex equipment. Each computer transfers status data to the duplex switching console. This data activates indicators and alarms, permitting maintenance personnel to determine the operating condition of each computer and to make quick decisions pertaining to duplex switching operations.

Information processed by the computer is sent via the display drum fields to the Display System, where it is converted as required and presented on cathode-ray tube (CRT) displays to the operators of the. Figure 3-6 shows the Display System, the associated drums, and the tie-ins to the MDI element.

The equipment contained in the Display System, for purposes of this discussion, is divided into the following major groups: the digital displays, the situation displays, and associated equipment. The digital and situation displays are made up of consoles housing CRT's which present a picture of the air situation to an observer. The associated equipment is made up primarily of various components connected with the operational functions of the displays.

The Display System provides the means by which the air situation of the area supervised by the Center is visually presented to human observers. This is accomplished by means of special CRT's mounted in specially constructed and equipped consoles.

Data is first accepted by the Input System and is subsequently transferred to the Display System via the Drum and Central Computer Systems. The tracks and raids representing the air situation are consolidated and converted into larger common co- ordinates for display at the consoles. Since all such data is received from the computer in binary form, the Display System converts the data from the binary form to a system of letters, numerals, vectors, and symbols. This conversion permits the presentation of a display which is more readily viewed and interpreted by the observer.

The console operator observing the air situation messages presented on the CRT may act on the information in several ways. The operator may communicate with the computer by requesting information from the computer, or by feeding back information in answer to a request from the computer. He may instruct the equipment to transfer a message to the console of another operator. These operations are possible through the use of manual-intervention switches and light guns located on the consoles. Telephone facilities located at the console are also available to the operator for communication with other personnel within the Center He may also communicate beyond the area of the Center by wire and radio telephone circuits.

The Display System employs two basic types of CRT displays for presenting the visualized air situation to the human observer. They are the digital displays and the situation displays. The CRT's for these displays are mounted in various types of display consoles located at selected operating positions in the Center. Typical consoles are equipped with a situation display (SD) scope, a digital display (DD) scope, and various manual- intervention (MI) switches, alarms, and warning lights. Many consoles are also equipped with a light gun and telephone facilities (fig. 3-7).

In addition to the display consoles, the equipment of the Display System encompasses various types of associated equipment, including auxiliary consoles (fig. 3-8), which aid the Display System in the performance of its functions.

Digital display data is processed by the computer and transferred in binary form via the Drum System to the Display System. Since data in binary form is difficult for an observer to interpret, the binary information is converted to analog voltages which, in turn, are converted to the visual display presented on the face of the DD CRT.

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The Output System transfers tactical information from the Center to other air defense installations. Having formulated an output message, the Central Computer System transfers the message to the output buffer (OB) fields of the LOG drum in the Drum System. The Output System then accepts the message from the OB fields and transfers it to the appropriate telephone terminal equipment for transmission to its destination.

• Ground-to-air (G/A) messages, which are sent to manned interceptors and guided missiles (the AN/ FSQ-8. however, does not transmit G/A messages);
• ground-to-ground (G/G) messages, which are intended for crosstelling to adjacent centers, higher echelons, and remote radar sites;
• and teletype (TTY) messages, which arc used for communication to higher echelons and antiaircraft batteries.

The G/A-FD and G/A-TD storage sections receive and temporarily store output messages that are to be sent from the Center to manned interceptors. This storage section transfers such messages to the telephone terminal equipment utilized in relaying messages to automatic, radio, data-link transmitters and thence to the interceptors.

The BOMARC 1 and BOMARC 2 storage sections receive and temporarily store output messages intended for guided missiles. The transfer of such data to its final destination takes place in the same manner as for G/A messages.

The G/G storage section receives and temporarily stores output messages that will be sent to other Centers. It transfers these messages to the telephone terminal equipment utilized in transmitting information to sites that have automatic input equipment.

The TTY storage section receives and stores output messages that will be transmitted to higher echelons or to remote nonautomatic sites. It transfers these messages to telegraph terminal equipment used to send output data to installations equipped with teletype receivers.

A typical floor plan of the original Direction Center is shown in figure 3-12. The associated power and air-conditioning equipment building (fig. 3-12) is a 1-story structure, 110 feet square, and approximately 21 feet high. It is connected to the Direction Center by a 22-by-100-foot bay that provides for storage and maintenance space, including a throughway for steam, water, and power lines. Adequate fuel storage is provided for the operation of the power plant.

Typical support facility requirements for a Direction Center are:

1. Administrative facilities
2. Officer quarters
3. Airman quarters -
4. Officer mess and club facilities
5. Airman mess and club facilities
6. Post exchange
7. Recreational facilities
8. Motor maintenance facilities
9. Installation administration and shops
10. Supply warehouses
11. Utilities and heating facilities
12. Security facilities
13. Officer and Airman family housing

The power and air-conditioning plant is a stepped. 1-story building 220 feet by 150 feet, half of which is approximately 25 feet high, and the other half of which is approximately 15 feet high. It is located near the Operations Building. A covered passage for cables and piping connects the two buildings (fig. 3-15).

Fuel storage and support facilities for the DC-CC site are the same as those described for the DC and CC sites.

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Chapter 4, Page 35

Both the AN/FSQ-7 Combat Direction Central and the AN/FSQ-8 Combat Control Central utilize tens of thousands of electron tubes and associated circuitry. Of these, more than half are processing air defense data at any given time. To assure continuous functioning of both Direction Central and Control Central, the following precautions are incorporated into each as basic features:

Because of the physical nature of the equipment and the importance of its function, the requirements for optimum reliability cannot be over-emphasized. It is one thing to develop equipment designed to solve the problems of air defense. It is something else again to be able to rely on that equipment for continuous operation with accurate results. The security of the nation demands that the SAGE System, in all its aspects, be unerringly reliable.

Error detection by the use of programs has distinct advantages. A program can be changed easily when the computer or any auxiliary components are changed. A program can be constantly improved. No extra equipment is required since the program uses the facilities that are already available. A program uses the machine in a more normal manner than does test equipment. A program that has been checked and accepted as a good maintenance tool is not subject to deterioration. B3 contrast, standard test equipment may be checked and accepted only to become unreliable shortly after being placed in actual use.

Maintenance programs are divided into two main classes, reliability programs and diagnostic programs. Maintenance programs used to detect the existence of errors are called reliability programs. A reliability program checks all or part of the computer for correct operation. Maintenance programs used to isolate machine failures known to exist are called diagnostic pro grams. A diagnostic program locates the machine fault as closely as possible.

Duplexing equipment makes it possible for one machine (called the standby machine) to be maintained in perfect condition without cessation in normal operations since its twin (called the active machine) is under. taking the processing of air defense data (fig. 4-1) Should a breakdown occur in the active machine, the standby machine takes over operations (thus becoming active), with the malfunctioning active machine now becoming the standby. The only delay encountered it this switchover would be met if the standby machine

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were undergoing corrective or scheduled maintenance. Such delay, however, would be very short.

Marginal checking (MC) is the method used to detect imminent circuit failures. The circuits are designed so that one or more of their associated supply voltage may be varied in prescribed amounts without causing circuit failure when the components are within accepted tolerances. Components outside of accepted tolerance require less voltage variation than normal to cause failure. Therefore, component deterioration can be detected by the amount of voltage variation required to cause failure. The voltage variation which causes circuit to fail is called the circuit margin. Marginal checking is not a maintenance tool, however, unless used with programs which operate the circuit to which the MC voltage excursions are applied.

The MC System serves to vary the MC voltages one at a time, over large sections of the system. For a more detailed reliability check, a breakdown of these large circuit groups is made on the expected circuit margins. A further breakdown is provided for the purposes of fault isolation in the event of a failure during a reliability test.

1. Repair of defective or marginal components removed during scheduled or nonscheduled maintenance of the Central
2. Test of pluggable units, and components such as tubes, crystal diodes, and rectifiers
3. Calibration and maintenance of test equipment

Test equipment is located in the maintenance and test area of the Central. Maintenance parts and special: tools are provided in the adjacent parts storage area.

To prevent power interruptions in the maintenance and test area from interfering with normal operation of the Central, the maintenance and test area is provided with its own independent power supply. This power supply provides power only for the special test equipment located at the Central.

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The organization of manuals for the AN/FSQ-7 and AN/FSQ-8 equipments is directly related to the divisions outlined above. Information concerning functional systems of the equipment can best be understood when compiled in manuals organized about logical divisions. On the other hand, installation, operation, maintenance parts listings (of physical groups), and special test equipment information can best be understood when compiled by physical divisions.

The manuals are structured to permit the reader to assimilate information in successively finer detail. Manuals not directly related to the equipment (theory) are organized to give the reader opportunity to stop at certain points in a manual and how the complete subject to a degree governed by the place at which he stops. This is possible because the divisions of the manuals are functionally complete and enable the reader to thoroughly understand the equipment, unit, element, etc. being discussed.

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Basically, each system manual is organized in the following manner. The logical function and theory of operation of the system is discussed in Part 1. The theory discussion is usually based on a simplified block diagram. The remaining parts of the manual are divided into the elements that make up the system. Each element is presented in a separate part and generally contains an introduction describing the equipment, a discussion of the role of the element in the system, and a detailed explanation of theory. The detailed theory of the element is based on logic diagrams.

If a further breakdown of the element is necessary, chapters are used and are also basically divided into general description and theory.

Each maintenance manual (except for the programming manual) is divided into seven sections:

These manuals are supplied without lists of contents, illustrations, tables, indexes, and title pages. In short, they contain nothing that does not directly pertain to specific maintenance tasks. Each page, however, contains appropriate headings (in code) for rapid location of specific procedures called for either by the card file or by a reference note in some other part of the manual.

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