1941: Radio

Frequency Modulation.

Broadcasters, public utilities, police, Civil Aeronautics Authority — all have found improved radio service with frequency modulation. Now frequency modulation is being used in marine broadcasting. At Boston Harbor, both quarantine officials and ship owners are more than pleased with the operation of the new General Electric F-M radio equipment which gives two-way communication between United States quarantine tugs and Quarantine Administrative Headquarters in the Custom House at Boston.

Each day the tugs go out five miles or so to subject to inspection all vessels entering the port. By means of F-M communication, the necessity for returning to shore to check records is eliminated so that ships are cleared more promptly and ship owners are saved expense in the fact that they know when they can dock so that they may make arrangements for longshoremen and other unloading facilities.

'Moving Day' for Broadcasters.

On March 29, 1941, radio stations with frequencies below 740 kilocycles were given a reassignment of frequency bands by the Federal Communications Commission (FCC). The frequency of a station, i.e., the carrier frequency, is held constant by means of a quartz crystal, no larger than a lump of sugar. Such a crystal vibrates at some fixed definite frequency, depending on its size and shape, and in so doing generates a minute quantity of electricity on its surfaces due to 'piezo-electric' effect. By means of vacuum tubes this electricity is amplified and used to control the carrier frequency of the station. The foregoing changes in station frequency mean, then, that all the stations affected were obliged to obtain new crystals that vibrate at the new assigned frequency. This did not, however, present any difficult problem.

The changes in frequency were made not only to reduce interference between stations in the United States, but also to harmonize better the stations in the United States, with those in Canada and Latin America. When the frequencies were assigned initially, the Latin American stations were few and relatively unimportant. Now there are several large stations below the Mexican border and incidentally the most powerful station in the Western hemisphere is the 350-kilowatt station in Mexico City, which is seven times more powerful than the 50-kilowatts maximum permitted in the United States. As a result of the increase in broadcasting stations in the Western Hemisphere considerable interference and confusion had developed.

The new frequency assignments were worked out harmoniously at a Western Hemisphere conference held in Havana in 1937. As a result Canada has six exclusive channels, Mexico six, Cuba one, and the United States more than 40. The harmonious determination of these channels was another step in the development of the 'good-neighbor policy' among the countries of the Western Hemisphere.

Police Two-way Communication System.

A two-way portable communication system weighing only 11 pounds and having a range of one-fifth of a mile has been developed by Gerald S. Morris for the New York Police Department. The apparatus is so compact and so divided that it is readily placed in special pockets in the coats of the policemen. From outside appearances it would be difficult to determine that the policemen carried a combined receiver and transmitter.

Mine Radio Communication System.

A radio communication system has been installed in the mines of the Maureen Coal Company of Spelter, W. Va., by means of which good communication is obtained between cars, miners, and shafts with a fraction of the cost of a standard telephone system, a set costing but $95.00. In addition, the radio sets have the advantage of portable operation. The high-frequency waves are carried by the 250-volt trolley system and power for operating the set is also obtained from the same trolley system. It is found that the best results are obtained when the trolley system is in reasonably efficient operating condition. Thus the radio system effects an incidental service for it provides instant evidence of poor trolley contacts, low-resistance grounds in trolley hangers, and other similar deficiencies. Several sets may operate over the same trolley system, it being merely necessary that they operate at different frequencies.

Measuring Public Taste.

For a number of years the broadcasters have been confronted with the problem of determining the tastes of the public for the different radio programs. The Nielson Radio Index has attempted to solve this problem by attaching an Audimeter recording unit within the cabinet of the receiver. The unit consists of a continuously driven tape, sufficient tape being provided for a month's supply. A stiff wire is connected mechanically to the tuning capacitor and this acts as a stylus to make recordings on the tape. The records so obtained give a minute to minute record of the programs, the times that they were turned on and off as well as the times when the receiver was turned on and off. Thus, by inducing different members of the community to operate such sets it becomes possible to determine the relative popularity of the different radio programs.

New High-Frequency Tube.

The General Electric Company has produced and placed on the market a new transmitting tube designed particularly for frequency modulation (FM) and television, both of which operate at very high frequency. The tube, the largest available for this class of service, is 7 inches in diameter and is less than a foot long over-all. It is a three-electrode tube with a special helically-wound grid within the copper anode or plate. The plate is water cooled and is capable of dissipating from 12 to 20 kilowatts depending on the class of service for which it is used. The design of the terminal mount and the folded (introverted) anode minimize lead inductance and make the tube particularly well adapted to high-frequency applications.

The tube is designed for use as an audio-frequency amplifier or oscillator or a class B modulator. A pair of such tubes will give a plate modulated carrier frequency of 25 megacycles.

Super-midget Tubes.

A new contender for the title of smallest tube has appeared on the scene during the year. The new tube of which there are two types, a tetrode voltage amplifier, and tetrode power amplifier are manufactured by the Microtube Laboratories of Chicago. The length of the envelope is slightly greater than one inch and the diameter is  of an inch. No base is used and the leads are tinned to be soldered into the circuit. The factors which make the small size possible are that the metal used for the plate has low emissive properties so that a suppressor grid is not necessary and deflector plates have also been eliminated. These tubes are designed for use in very small electronic equipment such as hearing aids and small receivers.

Powerful Aeronautical Ground Transmitter.

Culminating months of research and development, United Air Lines has disclosed the details of a new 5,000-watt transmitter, considered the most powerful aeronautical ground transmitter in the world. The system includes a new combination transmitter and receiver for planes and a giant antenna for ground reception which is said to eliminate static and other radio interference almost completely.

The combination transmitter and receiver for planes is novel in that it operates on ten different frequencies, any one of which can be selected automatically by the pilot. The unit measures 15 by 21 inches and weighs only 75 pounds and replaces the one now used by United which operates only on two frequencies and weighs 110 pounds. Using the new set, pilots on a plane in flight over Cheyenne were able to talk to ground stations on both the Atlantic and Pacific coasts simultaneously.

The new antenna is 1,200 feet long. 500 feet wide, 100 feet high and covers an area of approximately 600,000 square feet. A one-fourth inch copper-clad steel wire is strung around the four poles of the directional receiving antenna.

A feature of the system is a circuit which keeps the receiver silent, without static or other noise, until it is automatically switched on by signals from planes or other ground stations.

United also announces that new ground transmitters which will operate at ten different frequencies are being installed at key points along the system, superseding the 400-watt transmitter heretofore in use. These new ground transmitters are so powerful that their signal can be heard on the other side of the world.

Airplane Detection.

Repeatedly reports have come from England that R.A.F. fighter planes have some new device which enables them to detect enemy bombing planes, even in total darkness. Although the exact nature of this device has not been revealed, the device disclosed in U. S. Patent 2,230,929 to Joseph Lyman Huntington, of New York and assigned to the Sperry Gyroscope Co. might serve the same purpose.

In operation, very short radio waves of the order of 20 inches long corresponding to 600 megacycles are emitted and sent in all directions. The receiving antenna is a parabolic reflector which rotates several hundred times a second, at the same time the axis of rotation itself turns more slowly so that the receiving antenna sweeps all the way around. The antenna picks up the signal, reflected from the other plane, at only one position in its sweep, and this position is shown by the position of a spot of light on the end of cathode-ray tube. Hence, the position of the spot of light shows the position of the other plane. In peace times the approaching plane could itself have a transmitter and emit the radio waves, permitting greater efficiency in detection.

Automatic Control of Aircraft.

The problem of remote control of aircraft was initiated at the end of World War I, but because of the lack of stability of planes at that time and the primitive status of the radio art, the attempts were not successful.

Recently, two methods have been successfully developed. In one, the operator in order to control the movement of the plane sends into space a definite number of electromagnetic impulses using an ordinary telephone dial. In order to increase the range of this method it is necessary for the operator to follow in another plane. In the second method the pilotless plane is navigated automatically over a course of considerable span and is landed safely at the end of its journey. Moreover, the operation can be performed irrespective of weather conditions and without the presence of a control operator.

Six devices of novel design have made such automatic navigation possible.

The first is an automatic pilot which maintains the plane in proper flying attitude. This function is controlled by two gyros, the horizontal gyro, which through relays, and other servo-mechanism controls the ailerons and elevators to keep the plane in the proper flight attitude, and the directional gyro, which, through suitable mechanisms, controls the operation of the rudder.

The second device is the aircraft radio compass which is capable of operating the rudder controls to keep the plane on the desired course towards the desired guiding stations. The system essentially is a loop fixed on the aircraft which, so long as its plane is parallel to the magnetic lines of force of the radiated field, no electromotive force is developed within it. However, as soon as the plane deviates from the guided course, electromotive force is developed within the loop. This, through a rather simple circuit, in which the electromotive force is amplified, causes the rudder to be actuated to bring the plane back on its course.

The third device is the ultra high-frequency marker beacon which is associated with the radio guiding station. The marker operates at 75 megacycles to radiate out into space either a fan-shaped electromagnetic beam or an inverse cone of electromagnetic energy. As soon as the plane arrives over the guiding station this electromagnetic beam or the cone reach up to the plane to act on a radio circuit established in the plane. The space relation of the beam or cone and the circuit is such that the plane is automatically dispatched along toward the next guiding station. In this manner a plane can be flown automatically over a row of control stations arranged in a straight line or in any desired course.

The fourth device is an altitude-control mechanism. As the plane approaches the landing field, it passes over a series of control stations. Each station, by its radiated waves, causes the radio compass to guide the craft towards the next station. Each successive station causes the throttle to reduce the velocity of the glide until finally a station on the other side of the field causes the plane to maintain the proper heading into the wind until the wheels touch the ground. The impact of the wheels touching the ground causes the throttle to be closed, the tail drops and the plane comes to a full stop. If a strong wind makes the glide so steep that the plane would land too soon, a mirror fastened to the barometric altimeter picks up a beam of light which is reflected to a photoelectric cell which in turn operates the throttle to maintain the plane at the correct gliding speed.

The fifth device is the power control mechanism which maintains the correct gliding and landing speeds described above.

The sixth is the interlocking electromechanical system which coordinates and synchronizes the above automatic landing operation.

Several successful flights have been made between Patterson and Wright Fields in accordance with the foregoing automatic system of control. The pilot merely took off, let the controls alone, and the plane completed the flight and landed automatically. One of the first possible applications of such a system is to relieve the transport pilot of many of the routine physical duties, and also to relieve him of the difficulties of flying and landing in the fog.

Facsimile Speeds Air Reconnaissance.

It has now become possible to transmit in ten minutes a facsimile of an aerial picture, from a plane to a receiving station on the ground. The demonstration was made by the Finch Telecommunication Laboratories. A complete sending and receiving facsimile is contained in the airplane. The aerial photograph is made on a paper negative and developed in a high-speed developer, the time of developing being about one minute. The picture is then placed in a transmitter which operates in a manner similar to the usual telephoto transmitter. That is, the picture is wrapped around a cylinder, and while the cylinder rotates the intensity of the photo beam acting on a photoelectric cell is varied in accordance with the light and dark places in the picture during the scanning process. The picture signal as well as the voice is multiplexed on the same channel and is then transmitted by frequency modulation. The rate of transmission is about 8 square inches per minute or the total time for a 7 x 8 inch picture is about 8 minutes. The signal is applied to the F-M transmitter at the microphone input terminals. Synchronism between the sending and receiving cylinders is obtained by a voltage impulse at the end of each revolution. By reversing the polarity of the picture terminals the picture is recorded as a positive print that can be handled roughly without injury. The great utilitarian value of the system for military reconnaissance is obvious.

New Electrical Musical Instrument.

A patent No. 2,241,027 is issued to Ralph W. Bumstead of Westfield, N. J., and assigned to RCA describes a musical device which will play the tones of any instrument desired, utilizing the vacuum tubes and electrical circuits similar to those used in television transmitters. The apparatus operates on the following principle: two different instruments, such, for example, the piano and the violin may play the same note, that is the fundamental frequency of each will be the same, but the two instruments sound differently because of the harmonics or overtones. The fundamentals are pure tones such as are produced by tuning forks. For example, a tuning fork might produce a fundamental or pure tone of 256 vibrations per second, but the piano and violin notes would also contain upper octaves such as 512, 1024, vibrations, in different proportions. The number and proportions of these higher vibrations determine the characteristic tone of the instrument.

In Mr. Bumstead's invention a single element is used to produce the single fundamental and on this smooth wave the irregularities corresponding to the overtones are impressed to produce the desired final tone. To do this an iconoscope, the screen or camera on which television subjects are focussed, is employed. A scalloped wheel or tuning fork impresses the smooth or fundamental wave on the sensitive screen of the iconoscope. On this same screen is projected the silhouette of a mask cut to correspond to the desired wave. Since the response of the screen is different in the light and dark positions, the electric current that comes from the screen will correspond to the waves projected on the screen. This current is amplified and conducted to the loud speaker where it is converted into sound. By controlling the form of the mask, the note may be made to correspond to such different instruments on the organ, clarinet, flute, or some combination of such instruments. (See also MUSIC.)

Television.

Colored Television.

On Aug. 27, 1940, television pictures in color were successfully broadcast from the television transmitter of the Columbia Broadcasting System (CBS) which is located atop the Chrysler Tower and these telecasts were received in CBS headquarters. So far as can be determined, this was the first time that colored television pictures were ever transmitted over a television broadcasting system.

Early in 1941, CBS was able to demonstrate to members of the Federal Communications Commission and of the National Television System Committee the solutions to all the major technical problems in the five basic fields of the color television art. The CBS is now undergoing field tests to work out problems of commercial application so that colored television can be made available to the entire American television industry, when conditions warrant it.

Television Transmitters.

Both the General Electric Company's frequency modulation transmitter station W₂XOY and television transmitter W₂XB are located high on the Helderberg Mountains, south of Schenectady. Field tests made the previous year showed that it was feasible to receive telecasts directly from the Empire State Building in New York City with sufficient signal strength to justify rebroadcasting them through transmitter W₂XB. As a result of the tests a permanent relay station has been erected and placed on the Helderberg Mountains and is now in regular operation.

The fact that a station 129 miles from New York can receive television programs over the air from a central broadcasting station and rebroadcast them opens up possibilities of extending the area of television broadcasting without excessive costs.

Television Floodlight.

For television pickup or telecasting an extremely high intensity of illumination is necessary. With floodlights operating with incandescent lamps, the heat evolved when the necessary lumens are obtained, often becomes unbearable to the studio performers. To remedy this difficulty, the General Electric Company has produced a mercury floodlight for television purposes. In the unit are three, 1,000-watt mercury lamps each of which is smaller than a cigarette. These lamps are mounted together in front of a high-efficiency, cylindrical parabolic reflector. The heat generated by these lamps is carried away by water passing through the jackets of the lamps at the rate of one gallon per minute. The floodlight produces 195,000 lumens of light which is the equivalent of 750 foot-candles over an area of approximately 100 square feet or the lighting intensity out-of-doors on a reasonably fair day. At equal room temperature maintained by air-conditioning the sensible heat from the three, 1,000-watt mercury lamps of the unit is only about one-fourth that from general-service incandescent lamps giving comparable illumination.

The new unit is equipped with motor and gears for operation by remote control so that it can be turned to follow the movements of the studio performers and at all times provide adequate illumination for the television camera. See also TELEVISION.

1940: Radio

Frequency Modulation.

The year 1940 has seen great advances in frequency modulation (f-m) both in the number of broadcasting stations that have been put in service and in the demonstrations of its superiority over amplitude modulation (a-m) particularly where interference occurs. As is now quite well known, the effect of interference such as static is very much less with f-m than with a-m.

The 50-kilowatt station WIXOJ at Paxton, Mass., 46 miles from Boston has been in continuous operation.

During the year the frequency-modulated station W₂XOR of Station WOR of the Bamberger Broadcasting Service in New York City inaugurated a frequency modulation program daily from 9 A.M. until midnight, making 105 hours a week. It is one of the very few stations operating on schedules such as are employed by the conventional broadcast stations. The transmitter is located on the 42nd floor of the building at 444 Madison Avenue in a room directly beneath the roof, and a coaxial transmission line runs directly up to the radiator on the roof. The radiator is a 53-foot pole giving an antenna height 620 feet above sea level. The carrier frequency is 43.4 megacycles and is controlled by a crystal.

A conclusive demonstration of the superiority of frequency modulation (f-m) over amplitude modulation (a-m) was made by the noise engineers of the General Electric Co. in the vicinity of Steinmetz Hall at the New York World's Fair. The receiver was one that could be tuned to either an f-m station or an a-m station. The same program was broadcast from each station. With the 1,000,000 volt, 3-phase continuous arc discharge from the nine 60-cycle transformers in Steinmetz Hall there was practically no effect on the quality of the f-m program although the noise was not entirely eliminated. The a-m program was practically obliterated by the interference. (See also INDUSTRIAL SCIENTIFIC RESEARCH.)

Airplane operation is so highly dependent on radio communication for safe operation that the best system available should be used. Frequency modulation has demonstrated its superiority in radio broadcasting so that it was felt that it could be used advantageously for airplane communication. The advantages of f-m are the high ratio of signal to noise as compared with that for a-m and the small interference between the common f-m stations. Accordingly a number of flight tests were conducted near Albany, N.Y., using a 150-watt f-m and a-m transmitter located in an office building. Also signals were received from Major Armstrong's station at Alpine, N. J. These tests showed a distinct superiority of f-m over a-m for airplane service and there is little doubt as to the wide use of f-m in the future for this airplane service.

Police Network.

An outstanding example of the adaptability of frequency modulation to a state-wide emergency radiotelephone two-way system for state police is illustrated by its adoption in Connecticut as being the system best adapted to the police requirements in that state. The state is approximately ninety miles long and sixty miles wide and is divided into ten troop areas, each with its own headquarters. Obviously the location of the headquarters in each section was not the best location for a high-frequency transmitter. Two frequencies are used, 39,400 kc (kilocycles) for the fixed transmitter and 39,180 kc for the mobile transmitter. A 250-watt f-m transmitter is located at the center of each patrol area and is actuated by remote control from headquarters. Two-way transmission requires high frequency and with amplitude modulation the experience with the forestry service showed that the reception would be spotty, due in a large measure to ignition noise. This factor is practically eliminated by frequency modulation.

The Chicago police are also installing an f-m system. In the short time that the system has been in operation it has proved entirely satisfactory.

In order to meet the rapid increase in the demand for f-m transmitters the General Electric Co. has put on the market three new types of receivers. One is an S-tube table model superheterodyne-type having a frequency range of 39.5 to 45 megacycles, for f-m only. The second is a console model of the same receiver. The third is a 13-tube console superheterodyne type, designed for both conventional broadcast (a-m) and f-m (frequency-modulation) broadcast. The frequency range is 540 to 1,700 kc (kilocycles) for the a-m band, 2,400 to 7,500 kc, 7,500 to 22,000 kc for short-wave reception, and 38,000 to 44,000 kc for the f-m band. All the receivers may be used with doublet or dipole antennae.

In the audible broadcasting field the Federal Communications Commission has set aside 40 channels for commercial and educational broadcasting by the frequency-modulation system which it characterizes as 'one of the most significant contributions to radio in recent years,' and which is 'ready to move forward on a broad scale and on a full commercial basis.'

The General Electric Company has recently established a new short-wave broadcasting station, W6XBE, on Treasure Island, San Francisco Bay, and transmits regularly to South America and the Orient. Twenty Latin-American consuls and other government officials participated in the inaugural. This is the only international short-wave broadcast station west of the Mississippi.

Tubes.

Long-Life Vacuum Tube.

A new type of vacuum tube which is expected to give many years of continuous 24-hour service has been developed by the Bell Telephone Laboratories. The present tube gives about 18,000 hours life but the new tube will exceed this many times over. By comparison, after 22,000 hours' (2½ years) service only 55 per cent of the old tubes were in service whereas over 95 per cent of the new ones were. Such tubes will probably not come into general use in the ordinary radio receiver on account of their very high cost and the fact that they would probably outlive the set by a considerable time.

Hearing Aid Tubes.

Every year the smallest tubes yet appear on the market, usually for some special purpose, and there appears to be no limit to the smallness to which such tubes can be made. The smallest tube now appears to be the two new hearing-aid tubes made by the Raytheon Production Corp. These are two types, both filament pentodes designated as CK-505 and CK-505X. The seated height is 1 5/6 inch and the diameter of the glass envelopes is 0.55 inch. These tubes give a voltage gain of 225 with a plate voltage of 30 volts, and the plate current is 54 microamperes; the filament battery current is 30 milliamperes at 1.25 volts giving 37.5 milliwatts, and the filament voltage is 0.625 volt. Likewise R.C.A. has developed a complete new line of miniature or button-type tubes and sockets adapted to every purpose such as meteorological and geophysical instruments (as for example with small balloons), service man's test oscillator and other scientific apparatus.

These small tubes have made possible the very small camera-size portable radio receivers. (See below).

Electron-Multiplier Phototube.

In 1935 a Secondary Emission Electron Multiplier was invented by Dr. V. K. Zworykin, D. A. Morton and L. Malter in which a very high degree of amplification could be obtained. The tube operates on the principle of secondary emission from a series of caesium-coated surfaces. Two rows of small parallel plates are placed opposite each other in a long tube and the electric field is so arranged that an electron leaving any one plate is drawn diagonally to the plate diagonally opposite. The impact of each electron on the caesium-coated surface of the plates causes the secondary emission of from 2 to 5 electrons. The electrons thus move to successive stages each at a higher potential, and at the same time the electrons increase in numbers in a geometrical ratio.

The new Farnsworth Electron Multiplier Phototube combines a phototube having a cathode coated with caesium, which has high sensitivity, and an electron multiplier, all in one highly evacuated glass tube. The tubes are very sensitive and cannot only be used as sensitive electric eyes but they are also valuable in work involving the delicate measurement of light.

The Klystron Tube.

An intricate type of vacuum tube, originating in the laboratories of Stanford University and developed further by the Westinghouse Research Laboratories at Bloomfield, N. J., is capable of generating waves only four inches (0.11 meter) in length. Two torus-shaped copper tubes cause the waves to vibrate as high as 3,000,000,000 times a second. With the aid of a six-foot horn the waves may be focused like a searchlight beam and can be made to light a small flashlight lamp connected to an antenna. Other possible applications are the production of bodily heat for medical purposes and the increasing of the number of television channels.

Receivers.

Manufacturers continue to incorporate improvements in receivers. The Hammerlund Mfg. Co. has produced a new 'Super-Pro' receiver available for the two tuning ranges, 15 to 560 meters and 7½ to 240 meters. The improvements include a variable selectivity crystal filter, a new noise limiter designed to provide maximum suppression without affecting normal performance, and a new 'S meter' which makes possible reporting signal strength under almost any conditions. When the control is adjusted to the desired volume, all the other received signals of strength are in proportion.

Small Portable Receivers.

In 1939 the industry was startled by the enthusiasm of the public for the portable battery receiver set that came on the market at that time and the demands became so great that many thousands were sold in a short time. There now appears an even smaller receiver called by one manufacturer a 'Mini-Portable' which is about 9 in. wide, 4½ in. high and 3½ in. deep, about the size of a camera, and it has the appearance of a camera and is about as light to carry, one model weighing only four pounds. The type manufactured by the Lafayette Company is actually a 4-tube super-heterodyne covering the entire broadcast band 540 to 1650 kc. It has a 4-inch dynamic loud speaker, a built-in loop aerial, four 1.4-volt tubes, two 1½ 'A' batteries and one 67½ volt 'B' battery. Although the set has just been on the market a short time, its operation has been eminently satisfactory and many thousands have already been sold.

Multi-Pattern Cardioid Microphone (Multimike).

The Western Electric Co. has brought out a microphone with which by means of a six-position switch, six different response patterns may be obtained such as the 'ribbon' (maximum response at point and back), 'dynamic' (equal response from all directions), the 'cardioid' (response in one direction only), and three 'Hyper-cardioid' responses (large response at one side and lesser response at opposite side.) The advantage of such a microphone is that it permits speakers to have a large freedom of motion, and in public-address systems, when there are strong reverberations, the microphone may be switched so that the dead spots in the microphone may be pointed in the direction of the loud speakers and feedback and howling is thus prevented.

Hermetically-Sealed Crystal Units.

As is well known, quartz and other crystals when subjected to pressure generate a very small electromotive force (piezo-electric effect), and such crystals have a natural frequency of compression which remains very constant. Consequently they are well adapted to generating constant frequency for radio broadcast carrier waves. This is accomplished by placing electrodes on the crystal, thus forming a capacitor, and this capacitor through amplification with vacuum tubes controls the carrier or radio frequency. Such crystals may also be used to drive clocks. In order to protect such crystals from atmospheric effects such as dirt and moisture, the General Electric Co. has enclosed such units in hermetically-sealed tubes not unlike metal vacuum tubes in structure. The base is provided with the contact prongs just as the vacuum tube. Such crystals have a range of from 540 to 8,000 kilocycles, and the frequency remains constant to 0.0001 per cent per degree Centigrade.

Radio on George Washington Bridge.

An experimental radio broadcast system has been installed on the George Washington Bridge that connects upper Manhattan and New Jersey. At each end of the bridge a sign advises motorists to tune in to 550 kc on their dials. Motorists who tune in receive a one-minute local broadcast which advises them as to the proper lane to take for uptown and downtown. The transmitter is a 4-watt unit that feeds a cable strung along the rail the entire length of the 3,500 foot bridge. The message is first recorded on a magnetic tape and then is reproduced in the transmitter. If this system of advising motorists in their driving proves satisfactory, it is planned to install similar systems elsewhere.

Radio in Aviation.

Radio Compasses.

A patent has been granted to John B. Dearing of Ben Avon, Pa., and assigned to RCA whereby the position of a plane is indicated automatically to the pilot at all times by the intersection of two white lines on a map. Heretofore the pilot has determined the directions of the radio beacon stations by means of a direction finder and has plotted the two lines on a chart to find his position at their intersection. All this is now accomplished automatically by two radio receivers which tune in on the two stations with a loop antenna which responds best when the station is in the plane of the loop. As the antenna rotates, the strength of the signal varies. The receivers control the cathode beams which fall on a screen similar to that used in television receivers. The beams oscillate back and forth tracing out two lines on the screen and the directions of the lines depend on the bearings of the two stations. By means of a small projector a map is projected on the same screen so that the pilot sees the beams intersecting on it, which shows his position. In order to keep the map and screen oriented irrespective of the motion of the plane, the entire indicating apparatus is under the control of a gyro.

Infra-Red Plane Detector.

It is reported that the British have developed a sensitive detector for airplanes which responds to the radiation given off either by the engine or by the exhaust. Dr. Zworykin of RCA has explained that the device probably responds to the infra-red radiation which an object like an airplane engine radiates even if it is only moderately hot. These infra-red rays themselves are invisible to the eye so that apparatus to make them visible to the eye is necessary. The rays are gathered by a device which looks like a telescope and are focused on a thin film of caesiated oxidized silver deposited on a metal plate. This substance is particularly sensitive to infra-red light, and when infra-red light is focused on it, electrons are emitted from the lighted part. These electrons are drawn up a tube where they pass through magnetic lenses which focus them on a fluorescent screen which makes the image visible to the eye. These rays pass freely through haze and smoke but any fog, except a light one, stops them. Funnels of warships and the exhaust gases of internal combustion engines emit infra-red rays, so that they can be detected by this device.

New Radio Range Beacon.

By means of a radio beam which sweeps around the horizon 60 times a second, airplane pilots can now find their course to a fixed beam at all times. A dial on the instrument board displays a circle of light around which an indicating mark moves to show the direction of the plane from the beacon. Previous beacons confined the pilot to a definite course. He knows when he is on the course and is informed when he is off but he does not know how far off he is or the direction of the beam. Such beams are very unsatisfactory when the pilot wishes to fly around bad weather. Now, if he wishes to fly straight to or directly away from the beacon he needs merely to hold a mark steady on a scale.

The Western Electric Co. has developed a multichannel radio telephone for aircraft which provides for dial switch selections of any one of ten pre-tuned frequencies. The new transmitter develops more than twice the power of the conventional equipment. It is designed primarily for communicating with planes in airline service and with private planes.

Radio in Advertising.

See ADVERTISING.

Microsecond Radiography.

An X-ray tube which can make exposures of one microsecond (one-millionth of a second) has been developed by Dr. Charles M. Slack of the Westinghouse Co. A rectifier charges a bank of condensers to approximately 90,000 volts which is applied between cathode and anode of an X-ray tube in series with a spark-gap. The operation of a switch causes the spark-gap to flash which then provides a path whereby the bank of condensers discharges the 90,000 volts to the X-ray tube. Photographs such as those showing the instantaneous positions of a bullet passing through a block of wood are typical of the photographs which may be taken with the tube.

Phonograph Pickup.

Instead of the conventional needle for the pickup from the record of a phonograph, a new sound system for the home and commercial phonograph based on a minute vibrating mirror has been introduced by David Grimes, Chief Engineer of the Philco Corporation. A feather-weight sapphire follows along the groove in the record and actuated by the vibration of the sapphire a paper-thin aluminum mirror, heretofore used only on galvanometers and oscillographs or in research laboratories, reflects a tiny beam vibration of light which in turn responds to the sound variations recorded on the record. The beam of light is reflected to a small photoelectric cell (electric eye) which creates an electric current that corresponds to the sound recorded on the record. This current is amplified and reproduces the sound in a loud speaker. This system reproduces with a high degree of fidelity and with a minimum of scratch. Also, the sapphire bears so lightly on the record that the life of this latter is greatly increased.

Television.

Early in 1940 the Federal Communications Commission granted permission to those stations which had been successfully conducting television broadcasts on an experimental basis to change to a commercial basis with certain designated frequency bands. Accordingly RCA and other manufacturers projected a program of receiver manufacture involving the outlay of more than $10,000,000 by RCA alone. Later the Commission rescinded this permit on the grounds that since the art was in its early stages there was danger that it might 'freeze' standards in the present status and hamper technical research leading to greater efficiency. Accordingly, the program of receiver manufacture was abandoned. This ruling is a severe handicap to the development of television, for under the stimulus of commercial programs there is little doubt that an extensive expansion of television broadcasting and reception would have resulted. However, in spite of this severe handicap the television art has made rapid strides forward, although it has not become possible to test it on a wide commercial basis.

In 1939 it was pointed out that the widespread development of commercial television broadcasts was seriously handicapped by the fact that owing to its high frequency the practical limit to a television broadcast was about 50 miles from the transmitter and that it was impracticable to 'pipe' broadcasts any considerable distance as can be done with the ordinary sound broadcast which may be transmitted by cables and overhead lines at audio frequencies. This handicap has now been overcome by the use of relay stations or transmitters with antennae spaced about fifty miles apart and located on elevations so that each is in almost a direct line of vision with the next. Each relay station receives the broadcast from the one immediately back, amplifies the received signal and rebroadcasts to the next station. In this manner the range of television can be extended much further than seemed possible only a short time ago although necessarily the cost is much greater than with audio broadcasts which involve primarily the use of cables and overhead wires.

This method of relaying was exemplified by tests made with television by the General Electric Co. with the broadcast station on top of the Helderberg Mountains near Albany N. Y. The waves used for television broadcasting are so short that they travel in essentially straight lines, almost as do light waves. Hence the theoretical limit of coverage is the horizon. With the antennae on top of the Empire State Building, 1,520 feet high, the distance is a radius of 40 to 50 miles. The distance from the Empire State Building to the Helderberg Mountains is 129 miles but on account of the height of the transmitting and receiving antennae, 1,520 feet and 1,700 feet above sea level, it was possible to transmit the signal this much greater distance. The transmitting antennae at the Empire State Building are rhombic in shape; the receiving antennae are also rhombic in shape and are mounted on 128-foot towers. The transmitting band was 44-50 mc (megacycles) and at the relay station this signal was converted to a 66-72-mc channel and amplified to a 10-kilowatt level. The receiving antennae are some 6,000 feet below the direct line of sight from the transmitting antennae at the Empire State Building so that the receiving energy must arrive by means of refraction or diffraction. Although no definite date has been announced for the opening of this relay station, it is expected that the station will rebroadcast the NBC programs from New York interspersed with programs originating locally. Thus the region around Albany and Schenectady will be provided with a television broadcasting station.

The relay experiment was conducted still further when the weather observation station at Whiteface Mountain, which is in the Adirondacks, 4,872 feet high, picked up an Easter service broadcast from the NBC Empire State transmitter. The reception covered two jumps, 129 miles to Mt. Helderberg from which it was relayed, and 120 miles further to Whiteface. This is the longest distance over which a television broadcast has as yet been relayed.

On March 6 another notable telecast occurred when a portable RCA transmitting set in a United Airlines transport plane flew over New York City. Another plane equipped with a receiver accompanied the telecast plane and the passengers in the receiving plane were able to see themselves flying as picked up by the cameras in the telecast plane and relayed to them.

RCA Laboratories have brought out a newly developed light-weight, 25-watt, 300-megacycle, portable television field pick-up equipment. The apparatus was developed to meet the demand for television field stations comparable in compactness to present-day sound broadcasting units. In order to make the equipment highly portable the various parts have been assembled in small carrying cases varying in weight from 35 to 72 pounds each. The entire apparatus may easily be carried in a taxicab. The unit is more efficient than the usual field pickup equipment and yet is about one-tenth the weight and one-sixth the cost. Another portable transmitter, intended primarily for amateurs, employs a 2-inch oscilloscope tube. The mosaic across which the scanning beam sweeps is on the end of the tube and the signal is delivered by a capacitive coupling through the glass forming the end of the tube. The iconoscope or receiving tube is a standard iconoscope to a reduced scale, but operates at the same voltage as the standard type. These features make possible a lowered price and easy portability so that it should be widely available. Such developments tend to interest the public directly in television and bring it into more universal use.

Telephone Television.

A patent has just been granted to Dr. Vladimir K. Zworykin of RCA by which participants in a telephone conversation may see each other. The patent makes it possible to transmit pictures both ways over the wires at once. 'Blanking out' amplifiers at each end permits the transmitting tube to send and the receiving tube to show only alternate pictures in the series that are continually coming over the wire. One of these pictures only is visible to the person at one end of the line and the other is available to the person at the other end.

Advances in Television.

An improvement in television whereby 30 per cent more detail is obtained was demonstrated by Philco Radio and Television Corporation Engineers. The improved system uses 605-line screens in contrast to the present 441-line screens. The greater number of lines takes much of the fuzziness out of pictures and is an advance towards displaying television to large audiences on a large screen.

Also a new type of small, vertical, loop antenna, built into receivers, was demonstrated. This permits real 'plug ins' in contrast to the specially built dipole antennas which must be mounted on the roof tops. To use these new antennas, however, it would be necessary to polarize the signals with the waves polarized in a vertical rather than in a horizontal plane as at present.

Color Television.

On Sept. 4, the engineers of the Columbia Broadcasting System in New York gave a demonstration of television in natural colors. The reproductions had all the color values of the original so far as could be determined. The system employs a standard camera tube, a standard television channel and a standard white screen picture tube of more than usual brilliance. Color is introduced by the use of rotating discs containing red, green and blue color filter segments. One disc is placed in front of the camera and the other in front of the picture tube. The discs rotate synchronously at 1200 rpm and the light entering the camera during scanning passes through successive filter segments. At the receiver light passes through filter segments of corresponding color. The speed at which the colors follow one another is so great that the colors blend in the eye of the observer and a trichromatic reproduction results. With three different colors it would seem that three times as many pictures would be necessary. Actually it was found that twice as many gave a satisfactory result. Thus it appears that color television will be ready to follow immediately on the heels of commercial television broadcasts when these occur. See also PHOTOGRAPHY; TELEVISION.

1939: Radio

Undoubtedly the two outstanding developments in Radio Engineering during 1939 were the new frequency modulation system recently developed by Major E. H. Armstrong and the opening of public television broadcasting in the New York area.

Frequency Modulation.

The conventional broadcasting systems operate on amplitude modulation in which the amplitude of the carrier wave is varied in accordance with the amplitude of the audiofrequency waves produced by the voice or music. In frequency modulation the frequency of the carrier wave is varied in accordance with the frequencies of the audiofrequency waves produced by the voice or music. Frequency modulation has been known for some time; but prior to 1935 it was not considered as having any virtue, and it possessed inherent distortion characteristics.

In 1935 Major Armstrong announced that he had developed a system of frequency modulation that not only was free from frequency distortion but had marked advantages in its high signal-to-noise ratio. That is, the system had been made relatively insensitive to outside disturbances such as static. The success of the system depends on the fact that by introducing into the transmitted wave a frequency swing greater than can exist in natural disturbances and by designing a receiver which substantially is not sensitive to amplitude changes or small frequency changes, but only to wide frequency changes of the signal, discrimination against interference from noise, such as static is obtained. A broadcasting station of 40 kw. at 42.8 megacycles, owned by Major Armstrong, is in operation on the palisades at Alpine, New Jersey. However, not more than 20 kw. can be transmitted continuously because of the undue heating of the grids although the full 40 kw. has been delivered for short periods. The transmitter is remarkable in that it produces by far the highest power ever developed for any purpose at these ultra-high frequencies. Tests show that the reception is very clear without noise. The transmitter has been heard consistently on top of Mount Washington, N. H., at a distance of 275 miles. Although fading took place, this is readily compensated by a.v.c. (automatic volume control). Another transmitter used in the tests was located in Yonkers at the home of C. R. Runyon. The 15-tube receivers were constructed by General Electric Co. under the direction of Major Armstrong. Major Armstrong plans to give demonstrations in various parts of the country. Many of the new receivers are adapted to frequency as well as to amplitude modulation, and there is every possibility of a coming widespread change to this system.

Tests have also been conducted by the General Electric Co. at Schenectady where a 50-watt frequency-modulated and a 50-watt amplitude-modulated transmitter were constructed for purposes of comparison. These tests confirmed the fact that frequency modulation is much less subject to noise disturbance than amplitude modulation and a more definite and uniform service area can be established. A given area can be covered with considerably less power, and smaller radio-frequency tubes are necessary.

While at first it may appear that a comparatively large channel width is required for frequency modulation, channel conservation may actually result at the ultra-high frequencies used since stations separated only a few miles can operate simultaneously at the same frequency with scarcely any mutual interference area. Already stations are being erected to employ frequency modulation. For example, the Yankee Network is already erecting a 50-kw. station near Worcester, Mass.

Also the General Electric Co. has announced a receiver with a band from 39 to 44 megacycles for frequency-modulation reception and three bands for amplitude-modulation reception. The receiver has thirteen tubes and delivers 20 watts of audio power. In another model employing eight tubes the audio output is 5 watts. Provision is made in these models for television audio signals and for phonograph records as well. The Browning Laboratories, Inc., Winchester, Mass., has a Frequency Modulation Adapter which may be readily connected to convention receivers, or placed in a radio console, to adapt amplitude-modulation to frequency-modulation. Also, this same manufacturer supplies a complete kit for frequency modulation. It is possible that within a few years the present method of amplitude modulations will be replaced entirely by frequency modulation.

Television.

On April 30 public television broadcasts were begun in the New York area by NBC station W2XBS. The schedule at first maintained by NBC consisted of 25 hours a week. The regular programs, including plays, variety acts, etc., were run 8:30-9:30 Wednesday and Friday evenings. Saturday evenings have been devoted to sporting events picked up with mobile units. Film transmissions intended for installing and demonstrating receivers are maintained from 11:00 A.M. to 4:00 P.M. Tuesdays and Fridays and from 4:30-8:30 P.M. Wednesdays, Fridays, and Saturdays. A mobile truck was successful in broadcasting the Princeton-Columbia baseball game from Baker Field to the Empire State transmitter, from which it was rebroadcast. Similarly the six-day bicycle races were broadcast from Madison Square Garden.

Something like eighteen companies are manufacturing television receivers. In the lower price range is a model with a five-inch cathode-ray tube and 16 radio tubes. The set is equipped for two channels and sells for $189.50. A 22-tube model with a 14-inch picture tube sells from $395 to $540. A 'kit' without tubes may be purchased as low as $80, whereas one with sixteen tubes costs about $135. As near as can be judged, over 1,000 sets have been placed with distributors and dealers, and the public has purchased perhaps 500 sets.

In the practical operation of the receivers, distortion arises from two principal sources: the ignition systems of automobiles and trucks, and diathermy apparatus. The distance that the receiver should be placed from highways depends on the energy level at the receiver. However, a normal distance should be from 60-80 feet. Diathermy apparatus employs high-frequency currents for physical treatments, and even at a distance of a mile or so such apparatus has been known to affect radio receivers. Television will be affected much more than the radio receivers. The elimination of the influence of diathermy apparatus is a problem that may have to be faced in some communities.

The commercial possibilities of television are still unknown. Reception from a transmitter, except under exceptional conditions, is limited at best to a 50-mile radius, and on account of the very high frequency, there does not seem to be any practicable method at present of 'piping' programs to any great distance. Hence, it is not known whether advertisers would feel justified in financing programs that would reach such limited areas. Moreover, television sets in any area will necessarily be much fewer than radio receivers. Also television-viewing is limited to a few persons, it must take place in a semi-darkened room and demands continuous attention whereas with sound alone a person can be doing other things while listening. Again, the program itself presents many technical difficulties such as arrangement of stage and actors, and requires in televising outdoor events a high degree of skill since there cannot be any time for planning. Also the public has been educated to the high degree of perfection of sound broadcasting with its nation-wide hookups. Hence it may expect a service impossible to attain, in the beginning at least, such as large-sized, perfected pictures of world events as they take place. As has been pointed out, the static and other disturbances to which television is very susceptible injure a picture much more noticeably than a sound broadcast; and accordingly imperfections will occur. The public has probably forgotten the experimental stage of radio when crystal sets were in general use; and, hence, the growth and the future of television is highly uncertain at this time.

Orthicon.

The Orthicon is a new improved form of the iconoscope far more efficient than the conventional iconoscope and gives an output current which is a linear function of the light input. Considered the most important development in television since the advent of the iconoscope itself, it was invented and developed by Albert Rose and Harley Jams of RCA.

The present methods of Television depend upon the iconoscope, invented by Dr. V. K. Zworykin of Westinghouse and RCA, for its operation. This conventional type of iconoscope consists of an evacuated glass tube within which there is a plate covered with a mosaic composed of many tiny photosensitive globules. In transmitting, the optical image is focussed on the mosaic and the individual globules emit electrons, the number of which is somewhat in proportion to the light falling on them. This leaves positive charges on the globules which have emitted the electrons. The globules are insulated from one another and so retain their positive charges until the charge equilibrium is restored by the scanning beam. This scanning beam is an electron beam, produced in a side arm of the tube by means of the conventional electron gun. It is made to scan the mosaic horizontally and vertically by being deflected by magnetic fields. The mosaic is therefore traversed by a transversal line pattern several times a second. High electron velocity is necessary in order to maintain a sharp focus and to excite a high level of signal current. When the scanning beam strikes the globules of the mosaic, however, secondary electrons are emitted by the globules, which in a large measure depend on the positive charge induced by the action of the optical image. The current resulting from these secondary electrons is collected by the collector electrode, which is back of the mosaic plate and constitutes the signal current. Because of the high electron velocity in this beam, however, there are more secondary electrons emitted than are produced by the scanning beam; and since, with an insulated plate at a given potential, the number of electrons leaving the plate must be equal to the number liberated, some electrons fall back in a shower onto the mosaic; and as their distribution is not uniform over the mosaic they produce 'dark spots' in the image. Correction can, in part, be made for this by the use of a hand-controlled generator, but at best this correction is not perfect and shading and 'flare' occur at the edges of the picture. Also, this secondary emission has another undesirable effect by producing a retarding field at the surface of the mosaic, which reduces the emission of electrons caused by the effect of the light from the optical image. This cuts down the output of the iconoscope by a substantial amount. Again, the returning electron showers neutralize some of the positive ions liberated by the optical image and stored in the globules. The total result is that such a tube has an efficiency of only from 5-10 per cent. Hence it would be advantageous to eliminate these secondary electrons, caused primarily by the high velocity of the impinging scanning beam. In the conventional tube this high velocity is necessary in order to obtain sharp focus.

If slow-moving electrons are used, the secondary-emission difficulty is eliminated. However, a slow-moving electron beam is more difficult to focus since the electrons are more readily deflected by extraneous fields. Also, when such electrons strike the mosaic at an angle they produce a blur.

The Orthicon overcomes these difficulties, first by using in the electron gun thermionic emission and a cathode with a flat emitting surface. The parallel beam from the flat surface of the cathode goes first through a 1-mm. hole and then through a 0.004-in. hole, being emitted as a very fine beam. It enters axially a cylindrical tube surrounded by a concentric exciting coil. This coil produces a uniform magnetic field longitudinally along the tube. The electrons tend to follow along these parallel magnetic lines. The deflection for horizontal scanning is produced by two parallel deflection plates between which the beam passes. The plates are so proportioned that the beam leaves them parallel to the axis of the tube and enters the field of another exciting coil, whose field is at right angles to the axis of the tube and to the plane of the parallel plates. This coil gives the vertical component of the scanning. The beam leaves the coil, again parallel to the axis of the coil, and then strikes the mosaic at very low velocity and at right angles to the plane of the mosaic plate. The beam then releases the charge remaining after the release by the optical image. However, the velocity of the electrons in the beam is so low that the troublesome secondary electrons are not released. As with the conventional iconoscope, the signal current is conducted away from the electrode at the back of the mosaic plate by a lead. The development of the Orthicon is only recent, and so far it has been demonstrated only in the laboratory. Because of its superior characteristics, however, there is every probability that it will ultimately be put in commercial service.

Television Transmission.

The important limitation to which television signals can be received is the curvature of the earth. The short waves in television travel in essentially straight lines, and at a distance of 50 miles their distance from the earth becomes so great that as a rule the received signals are too faint for reception. At a high altitude, however, a receiver should pick up a program at much greater distances from the transmitter. To test this theory, on Oct. 17, a television photographer ascended in a luxury airliner 21,600 feet above Washington and took a picture of a man in the Empire State Building in New York, the distance being over 200 miles. Mr. Sarnoff, President of RCA, while being televised in the Empire State Building was asked to smile; and the photographer in the plane snapped the image being produced on his iconoscope screen. This was the first time that a television transmission had been received for any substantial distance over 50 miles. Moreover, it confirmed the theory that the short waves used in television do travel essentially in straight lines.

Also, contrary to the belief that the maximum distance to which television can be effectively transmitted is 50 miles, twenty local farmers, from Pinnacle Mountain (1,800 feet high in the Helderberg Hills, 12 miles from Schenectady), viewed the King and Queen of England as they inspected the World's Fair in New York. The broadcast originated in New York, 132 miles away, at an 1,800-foot elevation; and the line of wave transmission at 132 miles, theoretically, is 7,000 feet high, or 5,200 feet above the receiver.

Tube Development.

There have been several changes and improvements in tube design during the past year. For example, in the new design of tubes, the grid cap has been eliminated in favor of single-ended construction in which the grid connection is made by a properly shielded prong in the grid base. This design is becoming generally accepted by radio engineers, and it is likely that grid wires above the chassis of receivers will ultimately be a thing of the past. The loctal base, which engages positively with the socket, is an improvement that is important when shock and vibration are present. Tubes also have been combined in many combinations; for example, rectifiers with beam power-output tubes, etc.

Another outstanding feature in tube design is the development and use of small receiving tubes, such as the 'Acorn' and 'Bantam, Jr.,' types, which have made possible the large number of small receivers, such as the table-type portable sets; and such tubes, because of their small capacitance, have facilitated the uses of ultra-high frequencies. There is a new line of battery tubes designed to operate on 1.5-volt dry cells with excellent performance characteristics, and these tubes are the foundation of the 'battery portable' sets. Such tubes have been developed in diode, triode, diode-triode and pentode form.

The permatron, a magnetically controlled mercury rectifier, has been made available to the industry. Also, there have appeared in the laboratory several forms of 'beam-group' tubes, which operate on a radically new principle. Electron beams, similar to those employed in cathode-ray tubes are chopped into groups, and the groups are brought together into charge concentrations from which the output power of the tubes may be obtained. Hundreds of watts at wave lengths as short as 10 centimeters may be obtained by means of this method.

The most sensitive current-detecting device ever developed was designed by Dr. James S. Allen of the University of Minnesota. This consists of a vacuum tube 2 in. in diameter, which will measure the very minute current conveyed by a single electron passing down a wire every 5 minutes. This is 6,000 times as sensitive as the most sensitive current detector that has existed up to this time.

Receivers.

Probably the most startling and unexpected development in receivers is the 'battery portable' set. Such sets immediately became so popular with the public that thousands already have been sold. Strange to say, the set involves no new principles, but is merely the result of skillful engineering in the development of principles that have long been known. The line of 1.5-volt dry-cell tubes with their high efficiency is one important contributing factor which makes the sets possible. Also, the gains that could be obtained by the use of a tuned loop antenna were far in excess of what engineers had ever believed possible. The recent development of an efficient permanent-magnet dynamic speaker of small size also contributed to the success of this type of set. The sets, complete with batteries, weigh only 9 pounds and their sensitivity is remarkable. Their appeal to the public, however, is due to their being a complete self-contained unit, their easy portability, the low cost of operation and the low price, which is as little as $15.

In automatic tuning a selector has appeared in which a preselector will set up programs in 15-minute intervals for a week in advance. A volume control for motor cars which operates with wind pressure is on the market. In these sets the volume increases with increase in the speed of the car, so as to counteract the increased noises due to wind, vibration and the increased noise of the engine. Self-compensating capacitors have greatly contributed to the stability of r-f and i-f circuits. The sizes of electrolytic capacitors have been reduced materially, making sets lighter and more compact, when such factors are important. A permanent-magnet dynamic speaker only two inches in diameter is now available.

Frequency Monitor.

The Browning Laboratories, Inc., of Winchester, Mass., have placed on the market a precision frequency monitor whereby radio stations, as well as amateurs, may check their frequencies quickly and obtain a precision well within the rigorous requirements of the new regulations of the FCC. The monitor is adapted to be checked quickly and accurately against WWV (a standard frequency service maintained by the National Bureau of Standards). It is adapted so that frequencies may be read to 5,000 cycles or better on all bands with the possible exception of 5 meters; and it is possible to check numerous points along the amateur band. The monitor involves a rather ingenious circuit design, and the checking is made possible by a very stable 100- and 1,000-kc, standard built into the apparatus.

Wireless Phonograph.

A 'wireless' phonograph is on the market in which a small oscillator, placed on the phonograph, is modulated by the phonograph pickup. A radio receiver, located anywhere within 50 feet, is tuned to this oscillator and repeats the phonograph program. Thus phonograph speech and music can be reproduced in different parts of a large hall or in different rooms of a house.

The Voder.

On Jan. 5 the Bell Laboratories demonstrated for the first time the 'Voder' (voice operation demonstrator), and the Voder has been on demonstration continuously at the World's Fair since its opening. The Voder is an electronic instrument controlled by keys and capable, when manipulated by a skilled operator, of talking in any language and at any pitch level and at any desired loudness. It differs from the phonograph in that it actually builds up speech from basic constituents. Only two primary sources of sound are necessary. One generator produces the 'hiss' sounds of the voice, and the other gives out a saw-tooth wave similar to those produced by the vocal chords. The waves are rich in harmonics; and by means of filters, different bands of harmonics, ten in all and controlled by the keys, are permitted to pass in order to build up the desired words. A very high degree of skill is required to operate the Voder, as is evidenced by the fact that proficiency is attained only after a year's practice at 3 hours a day. The Voder is never stumped and has pronounced such complicated words as 'intercommunicability,' as well as involved sentences. It is true that it does have a characteristic voice, which may be called electrical in character.

Aviation Aids.

Work is still progressing in the matter of radio aids for aircraft. The development of the absolute altimeter by which the aviator could determine his actual distance above the earth immediately below him was described last year. Other forms of such devices are being developed. For years loop direction finders have been used to guide aircraft, as well as to determine the direction of the transmitter. During the past year, however, the Sperry Gyroscope Company and the RCA Manufacturing Co. have completed a loop direction finder which is entirely automatic. The system employs a loop antenna and a straight wire. The emf. induced in the loop is amplified and modulated with a 90-cycle current generated locally. The 90-cycle current is mixed with the emf. from the straight wire. The polarity of the resulting emf. depends upon the direction of the incoming wave. In this new system the 90-cycle current is filtered out and is applied to the electronic control of a reversible motor which turns the loop. The direction of the incoming wave is indicated by an arrow on the loop. When the course of the plane is in the direction of the arrow, the 90-cycle component disappears and the motor stops.

Medical Applications.

General Electric engineers have produced a high-voltage X-ray equipment of compact dimensions and low cost to be installed at the Memorial Hospital, New York, for research and cancer treatment. The tube operates at a million volts and 3 milliamperes. The power is taken from a 60-cycle, 3-phase system, and the transformer has no iron core but operates on the tuned transformer principle. The transformer is insulated by enclosing it in a tank filled with an inert gas under high pressure. The tank is 8 ft. high and 6 ft. in diameter, as compared with a room 52 x 32 x 36 ft. with an 800,000-volt equipment necessary in 1933.

Recent Books on Radio.

'Principles of Radio Engineering,' by R. S. Glasgow (Associate Professor of Electrical Engineering, Washington University; 520 pages, McGraw-Hill Book Co., 1936) is primarily a text for students in electrical engineering and gives a thorough presentation of the fundamentals of radio communication. It assumes a knowledge of the fundamental laws of electricity and magnetism; its mathematics does not extend beyond that of the usual undergraduate curriculum.

'Communication Engineering,' by William L. Everitt (Professor of Electrical Engineering, Ohio State University; (second edition), 727 pages, McGraw-Hill Book Co., 1937), treats communication engineering in the broadest sense, including telephone, telegraph and radio engineering in all their phases, and is designed for those trained in the principles of direct and alternating currents. The mathematical derivatives are direct and simplified, and there are illustrative problems and a complete bibliography at the end of each chapter.

'Radio Engineering,' by Frederick E. Terman (Professor of Electrical Engineering, Stanford University; 688 pp., McGraw-Hill Book Co., 1937) presents simply a comprehensive treatment of the more important vacuum-tube and radio phenomena, and is well adapted to beginners with a background of elementary alternating currents.

'Theory and Application of Electron Tubes,' by Herbert J. Reich (Associate Professor of Electrical Engineering, University of Illinois; 669 pages, McGraw-Hill Book Co., 1939), designed to ground the student thoroughly in the fundamental principles of electron tubes and associated circuits so as to enable him to apply them to new problems, is highly recommended as a treatise on its subject.

Books by Moyer and Wostrel (James A. Moyer and John F. Wostrel, Division of University Extension, Massachusetts Department of Education; McGraw-Hill Book Co.).

'Radio Handbook Including Television and Sound Motion Pictures,' (886 pp.) is planned to provide radio engineers, operators and makers with a complete digest of authoritative radio data in a single, indexed volume with descriptions, definitions, design data, tables and illustrations.

'Radio Construction and Repairing' (444 pp.) is a simple treatment of the construction, testing and repair of radio receiving sets, including television and short-wave sets, for the use of service men, amateurs, setowners and others interested in the practical aspects of set operation.

'Practical Radio — Including Television' (410 pp.) is a practical manual on radio fundamentals and radio receiving apparatus, describing radio, telephone receivers, vacuum-tube sets, amplification, construction and testing of receivers, and general applications of radio.

'Radio Receiving and Television Tubes' (635 pages), a practical manual describing the action of vacuum and gaseous tubes and their uses in radio and television receivers, industrial processes and precision measurements, gives special attention to television systems and ultra-short-wave tubes. See also NAVAL SCIENCE, AMERICAN; TELEVISION.

1938: Radio

Vacuum Tubes.

The successful development of a tiny radio tube whose possible applications include mechanical 'ears' for the deaf that are four times as sensitive as the present type, and police and foot-soldier radio receiving sets, have been announced by the Hytronic Laboratories at Salem, Mass., after two years of research. Developed primarily for the construction of an improved hearing aid, the miniature tubes are one and five eighths inches long and nine sixteenths of an inch in diameter. Hair-like filaments, small grids, and other parts correspondingly small make the use of magnifying lenses necessary during manufacture. The tubes operate from a small battery no larger than flashlight cells. It can be incorporated into a hearing aid no longer than four inches. Operating on a filament voltage of 1.4 volts, the tiny tubes have a drain of 0.070 ampere. The tubes are made in a triode, tetrode, input pentode, and output pentode.

These small tubes have reawakened interest in battery receivers; and some manufacturers have increased production, since such receivers are quite practicable for the farm and other places where electric power is not available.

Receiving Sets.

There have been several new developments in receiving sets. For example, in a development by the General Electric Company in collaboration with the Warren Telechron Company, known as 'time-tuning,' it is possible to preselect any one of five stations for any 15-minute period over a full 24-hour span. Once the day's and night's programs have been selected and set up in advance, it is not necessary to go near the receiver. It will turn on and off, change stations, and perform manual functions automatically. By means of a simple switch, the clock feature may be made inoperative when clock operation is not desired.

Also, the General Electric Company has brought out the 'beamascope,' a built-in shielded-loop antenna that eliminates the nuisance of outside antenna and ground connections. This antenna also has an added advantage in that it is shielded from the electrostatic component of reception and responds only to the electromagnetic component. Since noise such as static is stronger in the electrostatic component than in the electromagnetic component, this troublesome factor is materially reduced. This elimination is accomplished by rotating the beamascope until the electromagnetic field of the noise source is either eliminated or reduced to a minimum.

With one exception, all the new General Electric receivers are equipped with keyboard, push-button tuning. The tone monitor is a newly-perfected circuit which greatly extends the reproducing range, both high and low, in proper proportion. It corrects the effect of peaks, boom, and distortion of individual tones to give a balanced richer tone.

In order to realize the full capabilities of the high-fidelity receivers, a new triple-cone speaker has been designed by R.C.A. For handling the high-power input, a relatively heavy cone is necessary but this limits the high-frequency response. To overcome this disadvantage, a smaller and lighter auxiliary diaphragm is placed within the larger cone and fastened to it by a flexible base support. A compliant coupling in the large cone permits the small cone to be driven independently at high a-f. frequencies by the wire coil to which it is attached. A small metal dome is used to load the apex of the inner diaphragm to resonate with the stiffness between the apex and the voice coil. This speaker has a substantially flat response characteristic of from 50 to 7,500 cycles.

Probably the most novel innovation in receiving sets is the remote-control automatic tuning device developed by Philco, the details of which have not as yet been released.

The station selecting-and-controlling device has no conductive connection with the receiver, but contains a small short-wave transmitter which sends the appropriate signals to the receiving set. The station is selected by means of a dial on the small transmitter. This causes the proper impulse to be sent to the receiver, whose mechanism is set in motion to tune in the selected station. Also the volume may likewise be controlled, and the receiver turned off at will. The control device may be carried at will about a home.

Aeronautics.

Outside those connected with the aircraft industry, few realize the extent to which the commercial air lines are using radio facilities for maintaining regularity of schedule and safety in flight. The transmission of messages to and from the plane has improved greatly in reliability, partly due to increased power in both ground and plane transmitters and in more reliable receiving sets. For example, one manufacturer supplies a heating device with a thermostat to remove moisture, a frequent cause of failure. The most difficult obstacle in radio reception under all weather conditions is 'snow-static,' a general term for static caused by charged particles, whether they be due to direct snow, sleet, rain or fog. Snow-static has a hissing character. A quite successful attack has been made by the Bureau of Air Commerce by enclosing the loop in a circular metal tube which allows the magnetic component of reception to influence the loop, not the static, but when the pilot runs into snow-static, he switches from the conventional straight-wire antenna to this last. This loop may not be satisfactory when the static level is high, but even then reception is greatly improved.

Receivers are almost universally of the superheterodyne type, with a range from 150 to 15,000 kc. Another major improvement is the newly-developed simultaneous radio-range and weather-reporting station which transmits beam signals and voice signals at the same time. Formerly it was the custom for the pilot to silence the radio-range signals during the broadcast of weather reports, since both are assigned to the same frequency in any given locality. Transmission is effected by the use of from 50 to 4,000 cycles for the voice modulation frequency range with a band of 830 to 1252 cycles suppressed by means of a band filter, this band being reserved for the radio-range signals. The removal of this band does not seriously affect the intelligibility of speech.

The major airports are now equipped with traffic control stations operating at 278 kc. which contact each airplane as it comes within the vicinity of the airport, and direct its movements thereafter.

The Bell Telephone Laboratories have developed a new device which determines the direction from which the radio transmitter of an approaching airplane is sending signals, even though the weather conditions may make the plane invisible. A tiny green light speck is located on a frosted glass screen in accordance with the direction from which the plane is coming. The points of the compass are marked around the edge of the screen. The system provides for any of ten wave lengths which may be selected remotely. As any single pilot talks, the spot of light moves to its correct position on the screen of a cathoderay tube. A pick-up antenna of special design which may be located at any remote point is employed, and a single telephone line connects the antenna and the dispatcher.

The Bureau of Air Commerce has instituted a radio-range beacon system which transmits directional signals along four courses, two along the regular way and two to mark cross airway flying. In the opposite quadrants the signal A is sent by a directional antenna system, and in the remaining quadrants the signal N is sent. At the boundaries the A and N signals synchronize to produce a continuous tone which is used by the pilot as a guide. When the pilot is immediately above the towers of the station the tone ceases for the short interval when he is in the 'cone-of-silence.' This silent region can be used to determine the location of the airport, but with the disadvantage that the signal is negative, and silence may be due to failure of the signal or reception. To obviate this, the Bureau of Air Commerce is installing ultra-high-frequency beacon stations which give the pilot a definite signal when he is in the cone-of-silence. In the matter of blind landing, the National Bureau of Standards has experimented with an ultra-high-frequency antenna operating underground in the center of the airport to establish a satisfactory landing beam.

Altimeter.

The single most important contribution of the year to safer flight is the absolute altimeter. The altitude indicator generally used operates on the principle of the aneroid barometer and hence it cannot indicate absolute altitude with respect to the ground. It merely shows altitude with respect to sea level or some other initial reference level at constant pressure. If the barometric pressure or temperature vary, an error of several hundred meters may occur, and such an indicator is not adapted to blind landing. With the altimeter a 500-megacycle radio wave is transmitted from a small T-shaped antenna on the under side of the right wing. On this wave is impressed an 80-cycle audiofrequency wave. The combined wave is sent to earth and reflected by the earth back to the plane where it is picked up by a similar antenna under the left wing. A portion of the transmitter output goes as a direct wave to the receiving antenna. The receiving circuit essentially counts the number of 80-cycle beats between the time that the direct wave and the reflected wave is received. The 80-cycle wave is used because it is easy to count and the apparatus is simple. The ultra-high-frequency wave is used since it is easily directed and is free from static. The instrument will be extremely valuable in flight, for it will indicate the presence of hills and mountains, the cause of several airplane disasters. Statistics show that with such an instrument practically one-half of the major airplane accidents that have occurred during the past few years would have been avoided. The instrument will also be useful in nautical navigation during fog, to detect the approach of land and other ships.

Television.

Since 1935, field tests have been conducted in New York City by RCA-NBC, the broadcasting antenna being located on top of the Empire State Building. For example, on June 7, scenes from Susan and God featuring Gertrude Lawrence were broadcast. Picture quality both from the studio and the motion picture films have improved steadily and the receivers have also improved in simplicity and performance. With the opening of the World's Fair scheduled television programs will be on the air in New York and in other cities. The receiver will produce 441-line images. There will be several types of receivers offered, the picture tubes varying in diameter from 7 in. to 12 in. The price must necessarily be considerably higher than those for sound receivers since they are much more complicated, involving from 18 to 33 tubes. There is considerable activity among the manufacturers, and a definite interest awaits the reception of television by the public. (See also TELEVISION.)

P. T. Farnsworth has brought out an entirely new image-amplifier pick-up tube for use in the sending station of the television studio. It combines several important features of the iconoscope (the tube having an activated screen on which the image to be sent is focused) and in addition utilizes the principle of the control grid for amplifying the picture signal before the image is scanned rather than after it is scanned, as in all prior pick-up devices. The resulting tubes are free from the spurious 'shading' signal, and one form has a sensitivity about 10 times that of the conventional iconoscope.

General.

John Shepard of the Yankee Network is having installed on the top of Mount Washington, N.H., a steel broadcasting tower nearly 7,000 ft. above sea level and commanding a line of view into five states. The tower is to be used for experiments in frequency modulation invented and now being developed by Major E. H. Armstrong.

Westinghouse is radio-proofing pin-type high voltage power insulators by means of a newly-developed copper-oxide glaze which maintains good contact between tie-wire and insulator to eliminate charging current arcs. The object of the glaze is to reduce the high-voltage static which interferes with radio reception.