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.