1945: Radio And Electronics
Archives consist of articles that originally appeared in Collier's Year Book (for events of 1997 and earlier) or as monthly updates in Encarta Yearbook (for events of 1998 and later). Because they were published shortly after events occurred, they reflect the information available at that time. Cross references refer to Archive articles of the same year.
1945: Radio And Electronics
Pulse-time modulation (PTM), one of the most revolutionary advances in the technique of radio broadcasting, has been announced by the Federal Telephone and Radio Corporation. This new method of modulation differs as much from the conventional amplitude modulation (AM) as does frequency modulation (FM). Moreover, it is particularly well-adapted to the high-frequency bands toward which it has become increasingly necessary to allocate different radio services because of the crowded conditions of the lower frequency part of the radio spectrum. The system is characterized by being capable of transmitting several sound programs on the same carrier frequency. Each frequency is broken up into a series of triangular high-frequency pulses with a short interval between successive pulses, these pulses occurring at a rate of many thousands per second. Each pulse is free to move within a limited range without interferring with adjacent pulses. Movement of the pulses is controlled by the modulating signals, which in turn are controlled by signals from different channels which are produced by the several programs, such as speech, music or television. In each channel at regular intervals there are synchronizing pulses, some every six intervals, some every four and some every three. The receiver may be synchronized with any set of these synchronizing pulses and thus select any one program.
The system is adapted to the transmission of several sound programs from the same source of origin and at the same carrier frequency, so that one station may perform the same functions which now require several stations. For example, one sending station can send out twelve different programs, all of which are interwoven in the receiver, but any one of which can be selected by a multiposition switch. In addition, the system is capable of combining full color or black and white television reproduction with sound in the same channel, thus making for economy in operation.
It is also claimed that the system is inherently adapted to multichannel communication over beamed radio links with repeaters, which are expected to span new long-distance communication channels in the near future.
Recently (1945), a successful demonstration of the system was made at the headquarters building of the International Telephone and Telegraph Corporation, New York City, where two groups of 24 men each in separate rooms conversed at the same time on a single carrier frequency, the conversations going through relay stations at Hazlet and Nutley, N. J. Only one transmitter and one receiver were necessary at each location.
Western Union to Use Radio Relay System.
A new super-high-frequency relay system, involving an automatic microwave transmission developed by RCA, is to be used by the Western Union Telegraph Company to speed and improve its service between major cities in the United States. It is expected to replace many familiar pole lines and hundreds of thousands of miles of wire in the company's 2,300,000-mile telegraph network. Last spring (1945) an experimental radio relay circuit was established between New York and Philadelphia and it was successful in meeting all the tests imposed on it. The system involves radio microwaves transmitted by towers spaced approximately 30 miles apart. On the top of each tower is an automatic unattended radio relay which receives the incoming signal, amplifies it and sends it along to the next relay tower.
The system will provide a larger number of channels than are now available for handling telegraph traffic; it will provide circuits for new uses and for special leased networks required by large users. With this type of radio relay it is possible not only to send telegraph messages in multiple numbers simultaneously, and with the speed of light, but to transmit telephone calls, commercial high-speed facsimile, radio photos and frequency modulation (FM) broadcast programs.
In addition, it can be used to operate automatic typewriters and business machines at widely separated points. Other advantages over the conventional systems are virtual elimination of distortion due to interference; it is simpler, more reliable, and easier to maintain; there is less equipment and the cost of operation is lower.
Vehicular Telephone Service.
The American Telephone and Telegraph Company has announced plans for 2-way mobile radio-telephone service for vehicles and other mobile units. Telephones on automobiles or other mobile units such as boats and barges will be connected with a general telephone system so that a subscriber to the general 2-way mobile service can talk from an equipped vehicle to any of the millions of subscribers of the Bell System, and likewise the occupants of mobile units can be reached by such subscribers. To call a vehicle, the customer (1) asks to be connected to mobile service. His call goes through the local telephone office (2) and on to the control terminal (3) where a special operator signals the desired vehicle (4) by radio. The occupant answers, his voice going to the nearest receiver (5), thence by telephone wires via control terminal (3) to the local telephone office (2) and to the customer telephone (1). The operator of a mobile unit can originate calls merely by picking up his telephone and pushing the 'talk' button. This signals the vehicular operator and she comes in on the line, receives the number which he desires, and puts the call through in the regular way. Applications have been filed with FCC for permission to operate this service in several large cities of the United States.
Bureau of Standards Extends Broadcast Service.
The National Bureau of Standards Broadcast Service, which comprises the broadcast of standard frequencies and standard time at definite intervals from the Bureau's radio station, WWV near Washington, D. C., has been slightly extended by broadcasting 15 megacycles (mc) at night as well as in the daytime.
The service is continuous at all times from 10-kilowatt (kw) transmitters, except at 2.500 kilocycles (kc) where one kw is used, and in addition the standard musical pitch of 440 cycles, A above middle C is broadcast. From these broadcasts any desired frequency may be measured in terms of standard frequency, with the aid of harmonics or beats from auxiliary oscillators. The frequencies are now 2.5 mc, 7:00 P. M. to 9:00 A. M., and 5, 10 and 15 me broadcast continuously day and night. In addition, on all carrier frequencies there is a pulse of 0.005 second deviation which occurs at intervals of precisely one second. This consists of five cycles, each of 0.001 second, and is heard as a faint tick when listening to the broadcast. This provides a standard time interval for purposes of measurement as well as an accurate time signal. The audio frequencies are interrupted precisely on the hour and each 5 minutes thereafter with a 1-minute interval for station announcements.
Effects of X-Rays on Crystals.
On April 12, Dr. Clifford Frendel of the Reeves-Ely Laboratories, New York City, showed that X-rays and other radiations can alter the chemical and mechanical properties of quartz and other crystalline substances. This effect not only has great theoretical interest, but was put to practical use in the war effort. Millions of tiny quartz plates or crystals, about the size of a postage stamp, were used by the armed forces to control oscillator frequencies in radio communication. In the past, the frequency of oscillation of the crystals has been adjusted by bringing them to the proper thickness by mechanical means, which is a very delicate and time-consuming operation. By means of this new X-ray irradiation technique, the frequency may be adjusted rapidly to the desired value with a precision heretofore impossible.
Simplified F-M Receiver Sets.
In a recent meeting of the Institute of Radio Engineers in New York, Stuart W. Seeley of RCA described a new frequency-modulation (F-M) receiver, which for the first time makes it possible to build a receiver which realizes the advantages of FM at a cost comparable to that of standard amplitude-modulation (A-M) receivers. The F-M sets before the war required the use of one or more tubes whose functions were solely those of noise suppression. They contributed nothing to the volume of the receiver or its output. Furthermore, to make these tubes fully effective, considerable amplification of the received signal was necessary. Although both of these requisites added to the cost of the set, noise continued to be present when the strength of a received signal fell below a certain point, called the 'threshold level.'
The new circuit, called a radio detector, is insensitive to electrical interference of all kinds whether man-made by ignition systems, oil burners and domestic appliances, or natural, such as atmospheric static. The new circuit not only is free of noises below the threshold level, but operates equally effectively on strong and weak stations, and its incorporation in a receiver eliminates the need for additional tubes and parts that were considered necessary in F-M receivers. RCA has announced that this latest improvement will be embodied in future RCA receivers.
New Allocation for Frequency Modulation.
In a recent decision of the Federal Communications Commission, the frequency-modulation radio broadcasting band for the United States has been shifted from between 42 and 50 megacycles (mc) to between 88 and 106 mc. Six channels are assigned to television, one between 44 and 50 mc., three between 54 and 72, and two between 76 and 78 mc. Facsimile is assigned to the 106-108-mc band, the 50-54 band is assigned to amateur use, and the 42-44 and 72-76-mc bands to non-government fixed and mobile services.
Television Programs from Stratosphere.
The Westinghouse Electric Corporation proposes and has already conducted experiments by which television programs can be re-broadcast from the stratosphere. The system was originated by Charles E. Nobles, 27-year old radar engineer. This will increase tremendously the range of the broadcast and thus reduce the number of rebroadcast stations and the accompanying costs. With television, the cost of production and operation of the equipment is much greater than for sound broadcasting, both in the studio and in spot broadcasting, such as ball games, parades, etc. Moreover, television does not lend itself readily to general network hook-ups so that at best the cost of wide coverage is certain to be high. However, in order to obtain sponsors for the programs, wide coverage and low cost per unit receiver are necessary. The purpose of Stratovision is to give a wide coverage at moderate cost.
The difficulties encountered in network hook-ups in both television and frequency modulation (FM) are primarily due to the fact that very short wavelengths or very high frequencies are necessary. These short waves travel in straight lines so that the sending and receiving antenna must be in the line of vision. Owing to the curvature of the earth's surface, if ordinary towers are used the distance and hence the radius of coverage is limited by the horizon and is only 50 miles.
If, however, the broadcasting station could be elevated to a high altitude, the coverage would be tremendously increased, just as a man on a mountain can see a very much larger portion of the earth's surface than a man on a plain near sea level. Moreover, buildings and other similar obstructions interfere with these short waves. Although the longer waves used for ordinary broadcasting also travel in straight lines, and their coverage would thus be limited by the curvature of the earth's surface, they are reflected by the ionized Heaviside atmospheric layer extending from 50 to 200 miles above the earth, and accordingly these waves return to earth or 'bounce' back. These reflected waves are called 'sky' waves, and as they extend way beyond the horizon, they can cover distances far greater than the direct or 'ground' waves can cover. The ultra-high frequencies used with television and frequency modulation are not so reflected, so that only the ground wave, limited by the horizon, is effective. These are the reasons that television broadcasting stations are located on the highest elevations, such as the top of the Empire State Building, and Helderberg Mountain, Schenectady, N. Y.
With colored television, another difficulty has arisen. In the present state of the art, the largest power tube available for the high frequencies required by colored television is only 5 kw, whereas 50 kw is necessary for a 50-mile range. Moreover, the power requirements decrease with increases in antenna height, while the same field strength is maintained even with increased coverage. The foregoing are factors which have led to the development of the Stratovision system, in which an aircraft carrying the rebroadcasting and relaying equipment flies at a height of 30,000 feet. There are two primary effects which enhance the coverage of stratosphere broadcasting. One is the greater area of coverage obtained because of the high elevation above the earth's surface. The other is the matter of reflected ground waves. When broadcasting from one antenna to another, a wave hits the ground and 'bounces' up to the receiving antenna. The phase of this wave is such that it tends to nullify the direct wave through the air, so that adjustments in the position of the receiving antenna are necessary for correction, and such correction can rarely be made complete. This effect is almost absent in stratosphere broadcasting.
With ordinary broadcasting, the frequencies of voice and music are so low that nation-wide coverage can readily be conducted over telephone wires, so that the expense is not at all disproportionate. However, television, and to a lesser extent FM, employs such a wide range of very high frequencies that such telephone wires cannot possibly be used. Two systems for accomplishing wide coverage have been proposed and to a small extent experiments have been conducted with each. A co-axial cable, one in which a central copper conductor is supported by intermittently-spaced thin washers so that the dielectric is almost entirely air, is used to connect the different stations. Such a cable costs about $3.00 per foot and repeater-amplifier stations every 50 miles are necessary, so that the cost of wide coverage is so high that at present it appears to be prohibitive. Also, the coverage would be only a few miles either side of the line of route of the cable. Furthermore, the system would require years to install.
The second method is to employ a chain of radio relay stations, with towers every 35 miles. More than 100 such relay stations would be necessary to provide a hook-up between the two coasts. Such a chain would require years to construct, and the expense would also probably be prohibitive. Furthermore, each relay station introduces some distortion into the signals, so the less the number of relay stations the better. Neither system is capable of handling the high definition required by color television.
In the Stratovision system, an aircraft flying 30,000 feet up in the stratosphere acts as the rebroadcasting station as well as serving as one of the relay stations. No difficulty has been encountered in designing the aircraft for this purpose since it operates at slow speed, and merely circles around. It is planned that two aircraft be in the air all the time, one in service and the other as standby. Each plane would be on two 8-hour shifts, and the times would be staggered so that a plane is leaving and returning to the ground every 4 hours. The aircraft are equipped with hot-air de-icers, blind navigation and landing equipment, and a pressurized cabin. Since the aircraft fly above the clouds, the only weather difficulty that might be encountered would occur when landing, and this would happen only in case of a severe storm. Engine trouble under these operating conditions is rare. Each plane is to carry 4 television transmitters, 5 FM transmitters, monitoring equipment and relaying apparatus to handle 9 separate programs plus conventional plane-to-ground radio.
The advantages of the system are many. At 30,000 feet a 1,000-watt transmitter can produce the same field strength at the receiver as a 50,000-watt one near the ground. These small-power tubes can take care of the high frequencies needed for colored television. 'Ghosts' due to ground reflections are practically eliminated. Since the line of vision at 30,000 feet is over 400 miles, and the radius of coverage is over 200 miles, the planes can be located 400 miles apart, requiring only a total of 8 for coast-to-coast coverage, as compared with 100 for ground relay stations and 600 for co-axial cables. Moreover, the width of the belt covered is 400 miles for Stratovision, whereas at most it is 100 miles for ground relay and co-axial relay stations. Six more planes would give coverage for 78 per cent of the country's population.
Earth obstructions such as buildings and other elevations between the broadcasting antenna and the receivers would be absent. Spot news can be picked up and rebroadcast easily since the plane is always in a direct line of vision with the pick-up transmitter. For an area around Pittsburgh, it is estimated that eleven 50-kw ground stations would be required as compared with a single kw Stratovision station. Also, it is estimated that the cost per hour for Stratovision will be only $934, as compared with $13,290 for ground coverage.
Orthicon Television Camera Tube.
A new television camera tube of revolutionary design and sensitivity called the RCA Image Orthicon, which has been withheld from the public on account of wartime secrecy, has just been made public by RCA. The tube is 100 times more sensitive than the conventional pick-up tube and makes possible telecasts of persons and events hitherto impossible because of lack of sufficient illumination. To the many who are familiar with studio telecasting, the extreme brightness of the illumination together with the accompanying heat not only makes it unpleasant for the participants, but limits their time of activity. In contrast, it is now possible to show on the television screen bright images of persons illuminated merely by a candle. The tube has the following specific advantages: (1) ability to extend the range of operations to practically all scenes of visual interest, particularly those under low-lighting conditions; (2) improved sensitivity, permitting greater depth of field and inclusion of background that otherwise might be blurred; (3) improved stability which protects images from interference due to exploding photoflash bulbs and other sudden outbursts of brilliant light; (4) smaller size of tube, facilitating the use of a telephoto lens; (5) lends itself to lightweight, portable television camera equipment; (6) improved gain-control system that provides unvarying transmission despite wide fluctuations of light and shadow.
The tube, resembling a large flashlight, has an overall length of only 15 in. with a shank diameter of 2 in. and a head diameter of 3 in. It consists of three main parts, an electron image section, which amplifies the photoelectric current; an improved scanning section; an electron multiplier section, the function of which is to magnify the relatively weak video signals before transmission. The principle of operation is that the light from the scene being televised is focused by an optical lens on the photo-sensitive face of the tube, which emits electrons from each illuminated area in proportion to the light striking that area. A grid directly behind the face and maintained at a positive voltage accelerates the electrons, which strike a target, the electrons being held on parallel courses by an electromagnetic field. The electrons striking the target cause it to emit secondary electrons, leaving a pattern of positive charges corresponding to the scene being televised.
The back of the target is scanned by a beam of electrons from an electron gun in the base of the tube. These electrons are slowed down so that they will fall just short of the target except when they approach a section of the target having a positive charge. When this occurs, the beam will deposit just enough electrons to neutralize the charge, after which it will again fall short of the target and turn back until it again approaches a positively charged section. The returning beam with picture information impressed on it by the varying losses of electrons is directed at the first of a series of dynodes, which are targets from which two or more electrons are emitted for each electron striking it (secondary emission). Electrons knocked out in this manner strike a second dynode and this process continues with the strength of signal multiplying at each stage until the signal plate is reached and the signal is carried out of the tube to be amplified, and transmitted or broadcast.
Large Screen Television Receivers.
The General Electric Company has announced an improved radio-phonograph-television receiver which, by new electronic means, will produce much better pictures for the home than has been done heretofore. The picture is produced on a screen 16 by 22 inches and has several features that give contrast and brilliance not obtainable in pre-war receivers. In addition to the 5-inch receiving cathode-ray tube or kenetoscope, a parabolic lens and a correcting lens are used to project the picture to a mirror and thence to the screen. Also, new features have been added to the audio and phonograph systems whereby realism in recorded music not hitherto obtainable is now produced. More perfect balance is obtained at both high and low volume, and reproduction is free from needle scratch and chatter, prevalent in former machines. It is expected that commercial production will permit these sets to be available in the early postwar period.
Powerful Air-Cooled Tube.
The newly-developed Westinghouse WL-473 is an air-cooled pliotron capable of dissipating 2,500 watts without water cooling. It weighs only 3 lbs. and can easily be held in the hand. It is a forced-air-cooled triode with thoriated-tungsten filament. The forced air-flow required is 100 cu. ft per minute for maximum anode dissipation. The amplification factor is 22 and because of its low inter-electrode capacitances these tubes can be used as Class C radio-frequency amplifiers and oscillators at 60 megacycles with 100 per cent input. For this application the maximum ratings are d-c plate volts, 3000; d-c plate amperes, 1.4 average; plate input watts, maximum, 4200. The power output is 3,250 watts.
In other classes of service it can be used as an audio-frequency amplifier and modulator, Class B; as a radio-frequency power amplifier; Class B, 800 watts power output. The tube now is being used extensively in oscillators that provide radio-frequency power for induction-heating and dielectric-heating equipment.
The Lighthouse Tube, so-called because of its cylindrical symmetry and stepped elevation which gives it the appearance of a lighthouse, is a new member of the recent disk-seal family, and represents novel features in the design of tubes for ultra-high-frequency (UHF) or microwave operation. For UHF work the ordinary vacuum tube no longer functions satisfactorily. The external inductance and capacitance usually connected externally to the conventional tube are far too large for resonance at these ultra-high frequencies. In fact, the inductances and capacitances of the connecting wires themselves are far too great. Also, the stray inter-electrode capacitances among cathode, anode and grid are so large as to vitiate the operation of the tube. Moreover, the transit time of electrons between electrodes within the tube, which is negligible even at normal high radio frequencies, now becomes a factor which has adverse effect on tube operation. Also, with the usual tube construction, the tube itself radiates so much energy that there may be little or no useful output available.
To meet these difficulties the Lighthouse Tube is constructed like a UHF cavity resonator. The anode and cathode are in reality the opposite faces of a short metal cylinder which correspond to metal discs connected by the cylindrical side wall. The grid is placed in a hole at the center of the lower disc. The outer walls are made of a metal having the approximate coefficient of expansion of the glass, so that a glass-to-metal seal can be made where necessary. The high-frequency current penetrates the cylindrical metal walls only a thousandth of an inch or so. To increase the conductivity for this current, the inner walls are plated with a thin layer of copper or silver, which is so thin that it has negligible effect on the expansion of the metal as a whole. The metal walls confine the paths of the electronic oscillations to the inside of the tube so that there is no appreciable external radiation of energy. Another advantage of this construction is that it permits physical separation of the output and input circuits, which means electrical separation as well. Hence, there is negligible interaction between the two. The tube actually operates through space-charge control.
Unlike the usual tube, the Lighthouse Tube cannot be considered as distinct from the circuit or line to which it is connected, but is really a related and coordinated part, particularly with reference to wave length.
A supersensitive electronic tube with the functions of the grid and plate interchanged was described at the New York meeting of the Institute of Radio Engineers by William A. Harper of the Westinghouse Electric and Mfg. Co., who was responsible for its development. The tube is so sensitive that it can measure one-hundred trillionth (1/100,000,000,000,000) the electric energy of the average home reading lamp. The tube must be operated in total darkness to keep ordinary light from energizing the grid. Glass tubes to prevent stray electrons leaving and causing erroneous responses surround the wires which support the internal structure of the tube. A welded tungsten wire touches the glass to draw away any stray electrons from the surface which also might affect the accuracy of the tube. The tube contains a wire mesh that releases electrons when heated, as by the radiant energy in a light beam, a metallic mesh called a grid which acts as a control gate through which the electrons must pass and a plate which collects the electrons. The tube can measure accurately the energy released by the feeble action of the light emitted by a star many millions of miles away. When so used, astronomers attach the tube, which is connected to a photoelectric cell, to the eye end of a telescope. On the basis of the reading, the distance from the earth to the star can be accurately determined by trigonometric computation. During war time the tube was used in electrochemical analysis of metals and the detection of impurities in high explosive compounds.
Miniature Radio Tubes.
The RCA has announced the development of miniature electron tubes in its laboratories at Camden, N. J., which will permit the construction of smaller home radio receiver sets and compact radio-television-record player combination in post-war days. The new tubes, some of which are as small as the little finger, are a 'wedding' of the acorn type developed for the ultra-high-frequency field and the filament-type miniature tube developed in 1938. The tube has the cathode-type inner structure of the acorn and the small envelope and base of the filament-type miniature. It is estimated that these tubes will result in a saving of from 20 to 40 per cent in the size of equipment. During the war they were used exclusively for war purposes.
To the 100,000 people in the United States who are deaf, practically the only means available to them to replace the deficient sense is to use the sense of sight. This they do by watching people's lips as they form words and sentences. The Bell Telephone Laboratories has brought out a device which promises wide extension of aids to the deaf in making speech visible by projecting on the screen of a cathode-ray oscilloscope vibrating bands of light that have patterns corresponding to the words spoken into a microphone. The length of each record is about 2y seconds and vertical distances are bands of frequencies extending up to 3,500 cycles at the top. The greater the intensity of the sound, the denser the pattern on the screen. Hence, the picture on the screen shows the three basic dimensions of sound — frequency, time and intensity. Each of the different vowels, consonants and combination of these has its own distinctive pattern. The patterns can be combined to give words and hence develop into sentences. The same words spoken by different speakers would have similar appearance, although the shapes in the pattern would vary in much the same manner that the speech of different people varies. This apparatus opens some day the prospect of enabling deaf persons to use the telephone and radio and to conduct direct conversation.
The apparatus has not as yet been made available to the public, but a few sets are in use in deaf schools where experience is being obtained in the training of the pupils to read and interpret the sound patterns.
Portable Electron Microscope.
Although the art of electron microscopy has made tremendous advances during the past few years, until recently it still remained a laboratory instrument. Its different parts and accessories were large in number and uncoordinated, and its power supply equipment was bulky and unwieldy so that a skilled physicist was required to operate the instrument. Although the device has become more and more compact and simplified, it still remained an instrument which could be used only in a laboratory. However, as a result of a 3-year effort, the General Electric Co. has just produced the first truly portable electron microscope ever to be built. It is of suitcase size, occupying less than 3 cu. ft., can be readily carried by a single person, has only two electrical controls like the two knobs on a home radio, and operates as simply as a light microscope. It requires only 110-volts, 60-cycles for power supply so that it can be plugged into an ordinary lamp socket. Provision is made for adjusting the filament brightness to the optimum condition and manipulating the sample to focus it and for the inspection of such parts as are desired. Provision is also made for inserting and withdrawing the sample from the vacuum by means of a specially designed 'insertion gate.' It requires 3 minutes to evacuate the tube after the sample has been inserted, the evacuation being accomplished by a mechanical vacuum pump together with a differential pump, both of which operate from the 110-volt, 60-cycle supply. The magnification is of the order of 10,000. Detailed precautions have been taken to eliminate vibrations such as those due to the pumps and even noises since the microscope, because of its high magnifying power, is very sensitive to even minute vibrations.
A new Westinghouse electronic oscillograph that photographs electric sparks flashing past at more than 5,000 miles an hour is now giving aircraft engineers more data about the ignition systems of high-powered airplane engines than was ever thought possible before.
Once exclusively a laboratory tool but now built on an assembly-line basis, the cathode-ray oscillograph drives a magic stream of electrons in a pencil-thin beam to record the ignition action in engines, thus helping to solve the knotty problems encountered in producing faster and more powerful warplane motors, according to E. W. Beck, lightning arrester engineer, East Pittsburgh.
Working with an amazing rapidity and accuracy, the streamlined oscillograph takes pictures on regular camera film and makes impressions in much the same manner as an X-ray machine.
The electrical impulses to be studied are shot across the path of the electronic beam, forcing the beam out of its straight path and causing it to mark a record of the voltage on the photographic film. The time involved is also recorded, so that engineers have a graphic record of electrical events that occur in periods as short as 100-millionth of a second.
Thanks to this device, planes once grounded because of ignition trouble are now able to remain in service.
One of the major war-time 'secrets' is the proximity fuse or an 'electric eye' which when placed in the tip of a shell will explode the shell when it comes within 70 ft. of an object. The fuse consists of a small radio set placed in the tip of the projectile and operates on the principle of Radar. A small antenna starts radiating high-frequency waves as soon as the shell is projected from the gun. When these waves strike an object they are reflected and some are returned to a small antenna on the tip of the projectile. If the object is 70 ft or less from the projectile, the timing of the reflected waves is such that the projectile is detonated. In one type of radio set the power is supplied by a small storage battery which normally is dry, the electrolyte being held in a glass container. The shock occurring when the gun is fired breaks the glass and releases the electrolyte. In a later development by the Westinghouse Electric Corporation the battery was replaced by a tiny wind-turbine, the size of a pocket watch, which spun at 40,000 rpm to drive a generator, which in turn supplied power for the radio set. The difficulties involved in the design and operation of the radio set can be appreciated when it is realized that the concussion produced by the firing of the gun caused a sudden jump in velocity of the projectile and equipment from zero to 2,000 miles per hour in a space of 10 ft. This produced a violent force on the radio and other equipment, equaling thousands of times the force of gravity. In the same period the projectile attained a rate of spinning of 25,000 rpm. This required the most careful mounting of the delicate electric tubes, soft rubber for the most part being used as a cushion to alleviate the shock.
Signal Corps Wire-Laying.
As a result of the war the Signal Corps has devised new methods of laying communication wires, based on a specially designed coil and dispenser, employing ground vehicles and planes, or by the use of bazookas and rifle grenades without the use of reels.
The dispenser is about one ft in diameter, one-half foot in length, weighs 25 lbs. and contains about 3300 ft of wire. Planes have laid the wire over mountain peaks, deep valleys, and dense forests, sometimes at a speed of 110 miles per hr. Communication may be maintained during the laying process and two or more dispensers may be connected in series without making a splice. A container having a capacity of eight dispensers has been constructed, enabling a plane to lay a continuous 5-mile circuit. Bazookas and rifle grenades were used to make connections with advance patrols or strong points in no-man's land. It is expected that in peace-time this method of using planes will revolutionize the laying of communication circuits, particularly in remote and inaccessible regions.