1 JUL"81 y ELE July 1961 SAC's Primary Alerting System c0 Bell Laboratories Dialing Overseas Calls LIBRARY?)" Air -Drying for Microwave " %RATOq Systems -y A Self -Protecting Transistor RECORD Static Frequency -Generators www.americanradiohistory.com F. J. Singer, Chairman W. M. Bacon .T. A. Burton Editorial Board J. W. Fitzwilliam E. T. Mottram R. J. Nossaman W. E. Reichle H. W. Mattson, Editor A. G. Tressler, Associate Editor J. N. Kessler, Assistant Editor, Murray Hill Editorial Staff M. W. Nabut, Assistant Editor R. F. Dear, Design Editor T. N. Pope, Circulation Manager THE BELL LABORATORIES RECORD is published monthly by Bell Telephone Labora- tories, Incorporated, 463 West Street, New York 14, N. Y., J. B. FisK, President; K. PRINCE, Secretary; and T. J. MONTIGEL, Treasurer. Sub- scription: $2.00 per year; Foreign, $2.95 per year. Checks should be made payable to Bell Laboratories Record and addressed to the Cir- culation Manager. Printed in U. S. A. © Bell Telephone Laboratories, Incorporated, 1961. www.americanradiohistory.com Bell Laboratories RE C 4 RD Volume 39 Number 7 July 1961 Contents PAGE 235 SAC's Primary Alerting System H. J. Michael and H. M. Prudent 240 Overseas Dialing: A Step Toward Worldwide Telephony O. Myers and C. A. Dahiboni 246 Air -Drying Apparatus for Microwave Systems J. M. Jackson 251 A Self- Protecting Transistor for the E -6 Repeater W. M. Fox 254 Training Simulator for Flight Controllers F. W. Monsees 255 Static Frequency -Generators for Ringing Power W. F. Iiannenberg 258 Sapphires to Protect Telephone Satellites from Space Hazards John IV. West (leftl and Leif Rongved, surrounded by developmental models of Cover active satellites, discuss a brass frame for holding electronic equipment inside such a satellite (see page 258). www.americanradiohistory.com Closed circuit teleri,iun cameras focus on briefing oration gathered at these sessions forms basis for officer at sAc's nndcrground command post. Infor- "alerts" issued over Primary Alerting System. 234 Bell Laboratories Record www.americanradiohistory.com SAC has a force of bombers and missiles capable of prerenting war by deterrence. Bombers on the ground, however, represent a loss of strength in the event of attack. The Laboratories -developed Primary Alerting System gets them "upstairs" fast. H. J. Michael and H. M. Pruden SA C's Primary Alerting System "Peace is our Profession" is the slogan of the To obtain the extra precious seconds needed to Strategic Air Command, whose mighty retaliatory launch a maximum force, SAC now has in opera- force is a major factor in insuring continued tion the Primary Alerting System (PAs). This peace in the world. To fulfill its mission ade- system provides a ready -to -use communication quately, SAC must be ever alert -ready to go into network for broadcasting "alert" announcements action at a moment's notice. to all SAC bases, with emphasis on voice com- Under recently established "airborne alert" munication. It is a permanently assembled net- training procedures, a certain proportion of SAC'S work, furnished as a Bell System service. Spe- bomber fleet is airborne at all times. In addition, cially designed signaling and alarm arrangements a substantial portion of the bombers are on are incorporated to insure the reliability and con- "ground alert" status. These are always ready tinuity necessary in so important a service. to take off, to be airborne within minutes after The Primary Alerting System was developed receiving warning of an attack. In this business, at the request of the Air Force. The A.T. &T. Co., time is precious. Every second cut from the Western Electric Co., and Bell Laboratories time lapse between first awareness of attack to worked with customary teamwork, and the sys- the command to "scramble" means more bombers tem was planned, designed, manufactured, and in the air, ready to carry retaliatory devastation put into service in less than one year. to the enemy, and fewer vulnerable bombers on The Air Force has two prime requirements: the ground. (1) that the network always be immediately avail- Playing a vital role in cutting this time lapse able to broadcast alerts; and (2) that it have is communications -getting immediate word of maximum reliability. To provide the desired imminent attack to all the far -flung SAC bases. availability, the system uses a so- called "hot- line" July 1961 235 www.americanradiohistory.com arrangement. In this way, the voice path is lines going out to its associated bases. Thus, there always available directly from a controller to all are two separate lines to each Air Force base, bases with no intermediate switching required. laid over separate routes and using separate In order to visualize the function of the alert- equipment; one line goes direct from SAC head- ing system more easily, a brief description of quarters and one goes via the NAF headquarters. SAC'S geographical organization is in order. SAC (For reasons of economy, overseas bases will not headquarters, the nucleus of the command, is in all cases have direct circuits from SAC head- at Offutt Air Force Base, Omaha, Neb. Major quarters, although they will be reached via two subordinate commands within the continental alert circuits.) Each line also appears in a console United States consist of three numbered Air at headquarters, and it is possible to hold conver- Forces and a missile division. These Numbered sation on a selected line without causing interfer- Air Force (NAP) bases exercise authority and ence on any other line. control over all SAC units within three geograph- ical areas covering the eastern, central, and Continuous Supervision western portions of the United States. More than As a further measure to insure reliability, all sixty SAC bomber units are located within these lines, including the circuits on each base, are three areas. under continuous electrical supervision and have As a step in providing the required reliability, suitable alarms at the originating -headquarters the system designers employed dual 4 -wire lines end of each circuit. This provides SAC with an throughout the network. This is illustrated in "up -to- the -second" status check on each circuit. the simplified layout of the network shown below. Because the continuity of all circuits must be All outgoing lines bridge at SAC headquarters checked, even while they are in use, a frequency - and radiate outward to the Numbered Air Force sharing, or "slot," signaling technique is used. headquarters and their associated Air Force This technique requires that a band about 250 bases. At each NAF headquarters, the incoming cycles wide be derived in the normal speech chan- line from SAC is .permanently connected to other nel. All signals are transmitted in this 250 -cycle ` Rf uNf LINES TO All OTHER SAC BASES SAC HEADQUARTERS LINES TO ALL f OTHER NAF HOS. AIR FORCE ;4 BASE LINES TO ASSOCIATED AIR FORCE BASES LINES OVER SEPARATE ROUTES NUMBERED of communication lines for AIR FORCE Network HEADQUARTERS Primary Alerting System with circuits interconnecting SAC headquarters, Numbered Air Force bases, and their associated air bases. 236 Bell Laboratories Record www.americanradiohistory.com Senior Controller at SAC underground headquarters in Omaha places a test call over the PAS "Red Phone." slot. The basic talking and signaling path for all returns an answering pulse at a lower frequency circuits is outlined in the diagram on page 238. to headquarters on the "receive pair" of the As indicated, band- rejection filters isolate all circuit. The originating end of each circuit is telephones and loudspeakers connected to the equipped with a receiving circuit synchronized voice circuits. These filters prevent listeners with the pulse- generator circuit, so that only from hearing the signaling tones and keep voice pulses received at the correct time are accepted currents from interfering with signaling. as valid reply pulses. These receivers are All signals are transmitted over the voice cir- arranged to send alarms to both Air Force and cuits by carrier telegraph terminals, designated Operating Telephone Company personnel if the "43A1," which operate at voice frequencies. Dif- reply pulses fail to arrive after 20 seconds, or if ferent frequencies are used for signaling in too many false pulses are received. opposite directions to prevent confusion in the Circuits on the base itself are also checked for signaling system if the two sides of a 4 -wire continuity by a flow of direct current. If this circuit cross each other. current is interrupted, the tone pulses normally The signals passed through the 43A1 terminals returned toward the headquarters are blocked. are simple and highly redundant. These charac- This causes the circuit to send an alarm. teristics help to insure the reliability of the sys- The alerting and acknowledgment signals, tem, even under adverse conditions. The signals which are sent in opposite directions, are 100 - include those for: testing circuit continuity in millisecond pulses transmitted at the rate of five both directions; sending alerts toward the bases per second for three seconds. The electronic, slow - and acknowledgment signals toward headquar- pulse repeaters at the bases prevent retransmis- ters ; and a call signal toward headquarters for sion of these pulses. non -alert calls. The arrangements for these A call signal of about one second is used for signals and their purposes will be explained below. calling headquarters from the bases. This call sig- Circuit continuity is checked by transmitting nal and the acknowledgment signals are auto- a short tone pulse every three seconds on the matically timed, and are produced by momentarily "send pair" of the four -wire circuit. Each Air operating the proper key. Force base has an electronic pulse repeater that All alerts are initiated and all circuit alarms July 1961 237 www.americanradiohistory.com and individual acknowledgments are indicated quarters.