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.