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.