Broadcasting (Jan - June 1940)

tally competitive" stations in the same center of population to serve the same area. The present system of classification employed for standard stations will not be used. Instead of having a clear channel station, several regionals and a local station in the same market the Commission proposes to license all stations in that area to do an identical coverage job. That does not necessarily mean identical power, which becomes secondary but, based on the prescribed "radiation index" formally to be announced later, it will be possible to determine coverage through application of the power-plus-antenna-heightplus-antenna-effieiency formula. Similarly, the existing situation whereby broadcast stations have a differential in daytime and night coverage, because of the vagaries of the standard broadcast channels, will be avoided with FM. Coverage of stations will be substantially the same both day and night. Power Provisions There will he no limitation on power, so far as indicated, except the very limitation imposed by the state of the art itself. Manufacturers apparently are unable to build efficient transmitters of greater output than 50,000 watts and probably that will be the limit, for the present. Tentatively, FCC engineers are talking in terms of staggered power ranging from 50 to 50,000 watts. The logical power sequence appears to be 50, 100, 250, 500, 1000, 2000, 5000, 10,000, 25,000 and 50,000 watts. As for station classifications, they probably will be in terms of low radiation index, medium RI and high RI. Stations in the high RI might be those using antennas of optimum efficiency, with 50,000 watts on channels in which the separation would be about 300 miles. FM transmitters should not cost as much as standard broadcast transmitters of equivalent power, it is thought in engineering circles, since the apparatus is lighter in weight, takes up less space and generally does not require as much material. Antenna costs, however, might be as much or possibly more, because of necessary heights. However, this does not hold true in centers of population where high b"uildings are available and where the mast can be extended atop the building. Receiving sets, according to the weight of testimony at the hearing and based on further informal studies, are expected to run slightly more than standard receivers, in view of the added "limiter" stage. Mass production, together with the development of small loudspeakers, with accordion-pleated cones, which give high-fidelity reception, should contribute to reduction in receiver cost. Manufacturers of FM receivers, a half-dozen of whom already are licensed for the Armstrong wide-swing system, plans to turn out combination AM and FM receivers and immediately launch merchandising campaigns designed to gear up production and gradually decelerate retail prices. Any hint of priority to existing {Continued on page 90) Prospective Coverage ofFM Stations COMPOSITE preliminary engineering opinion on coverage of FM stations of varying powers indicates a radius ranging from 19 miles for a 100-watt station to 72 miles for a 50,000-watt station under what might be regarded as average conditions. The following tabulation indicates this composite technical opinion, with the antennas specified calculated to provide some gain: Power (Watts) 100 250 1000 5000 50000 Antenna Height (Feet) 150 200 500 500 500 Radius (Miles) 19 26 46 57 72 Area (Square miles) 1135 2160 6650 10200 16250 Text of FCC Report Authorizing Commercial FM FREQUENCY modulation is highly developed. It is ready to move forward on a broad scale and on a full commercial basis. On this point there is complete agreement amongst the engineers of both the manufacturing and the broadcasting industries. A substantial demand for FM transmitting stations for full operation exists today. A comparable public demand for receiving sets is predicted. It can be expected, that this advancement in the broadcast art will create employment for thousands of persons in the manufacturing, installation and maintenance of transmitting and receiving equipment and the programming of such stations. Experimental stations have been operating over a number of years on frequencies above 25000 kc. for the development of such frequencies for rendering a regular broadcast service. A number of these stations employed FM and others employed amplitude modulation. After extensive hearings and investigations, the Commission has concluded that FM has advanced to the stage where broadcasting on a commercial basis is desirable in the public interest. The Commission believes that this is one of the most significant advances that has been made in aural broadcasting in recent years. How They Differ Briefly the basic differences between amplitude and frequency modulation are as follows : Modulation is a process of imparting sound or other signal (intelligence) to a transmitted radio wave. The radio wave has two defining characteristics — amplitude and frequency. With amplitude modulation the sound controls the amplitude of the radio wave transmitted, while the frequency remains constant. In contrast, frequency modulation varies the frequency of the radio wave while the amplitude remains constant. Up to the present, amplitude modulation has been used exclusively for regular as distinguished from experimental radio communication. The principle of FM has long been known but its practical use was not demonstrated until recently. The hearing yielded a vast amount of information as to the use of FM in broadcasting on high frequencies. Each interested party agreed that FM is superior to amplitude modulation for broadcasting on frequencies above 25000 kc. The record leaves no doubt of the fact that a regular broadcast service can safely be initiated on high frequencies using FM. The use of a wide band of frequencies makes possible a reduction of noise to a greater extent than attained with amplitude modulation. Man-made electrical and atmospheric noises consist primarily of amplitude variations and therefore frequency modulated signals have an inherent advantage in discriminating against noises. Experimental operations assured another advantage for FM, namely, that broadcasting stations could be operated on the same channel without objectionable interference with much less mileage separation than is possible with amplitude modulation. FM has the ability completely to exclude all except the strongest signal. The opening of the new band for commercial broadcast will help to correct numerous defects and inequalities now existing in the standard broadcast band. These inequalities result from the scarcity of frequencies, their technical characteristics and the early growth of broadcasting without technical regulation. There is today a lack of stations in some communities and other communities do not have sufficient choice of program service. The establishment of the new broadcast band in the higher frequencies will enable many such communities to have their own broadcast stations. The licensing of classes of stations in the same area with different frequencies and different power has resulted in a wide For texts of FCC report on FM-Television allocations, orders adopted covering commercial FM and other FM news developments see pages 76, 84, 85, 86 and 90. disparity in the extent of service to the public. The system of classification now employed in the standard broadcast band will not be used for licensing FM stations. In the rules and regulations and engineering standards to be issued in the near future information will be provided whereby applicants may apply for facilities to serve a specified area. Stations will be rated on the basis of coverage rather than power. Competitive broadcast stations in the same center of population will insofar as possible be licensed to serve the same area. Service Range The service range of the new stations while limited will, in many cases, be greater than that obtained from the primary service area of comparable standard broadcast stations. Stations a relatively short distance apart will not create mutual interference of a type that has rendered allocation problems both national and international so diificult in the standard broadcast band. The coverage will be substantially the same day and night. The present situation of certain stations in the standard broadcast band having large daytime coverage and restricted nighttime coverage on duplicated channels will be avoided. However, PM stations have not demonstrated the long distance coverage properties such as obtain with present high-powered clear channel stations. Accordingly, amplitude modulation stations in the standard broadcast band may be required indefinitely for the purpose of giving widespread rural coverage. For coverage of centers of population and trade areas, the new class of stations offers a distinct improvement. Experimental FM stations rendering program service have employed a channel of 200 kc. There is testimony to the effect that a band width of less than 200 kc. can be used, but this entails a reduction of the noise-discriminating quality which has been established by experimental operations utilizing a channel width of 200 kc. Testimony advocating a narrower band width was not supported by experience in program service. Moreover, the narrower band width would make less feasible multiplexing of facsimile and binaural transmissions on the same channel. In addition, the Commission believes that a regular program service should begin on a 200 kc. band basis which can be conveniently reduced if technical developments warrant. A further question at the hearing was the possible future effect on the service rendered by standard broadcast stations should an additional broadcast band in the high frequencies employing FM be established. There was agreement that the new and additional service would not supplant the service of standard broadcast stations generally and that, therefore, this service will not make obsolete the receivers now in use. Standard broadcasting is on an entirely different frequency band from that to be occupied by FM. FM will not interfere with it. Present standard broadcasting will continue, and certainly for a number of years will render full service. The extent to which in future years the listeners will be attracted away from the standard band cannot be predicted. Testimony at the hearing indicated that the manufacturers will provide receiving sets capable of receiving both standard and the FM broadcasts. The record is clear that the frequency space heretofore allocated to high-frefrequency broadcasting is not sufficient to establish a wide-spread service employing wide-band FM. The testimony indicates that advantages are to be had by the use of a continuous band for high-frequency broadcast stations which includes non-commercial educational stations. Therefore, the Commission deems it in the public interest to allocate a continuous band that wiU suffice for both commercial and educational stations. „ The frequency band of 41000 to 42000 kc. is now allocated to educational stations on a regular broadcast basis, and most of the activity of experimental stations using FM has been in the band between 42000 and 44000 kc. There is testimony to the effect that commercial broadcast stations employing FM should be permitted to operate in the frequency band between 42000 and 50000 kc. principally for the reason that this band is particularly suited for rendering an FM broadcast service. The effect of sky wave interference will not be known until additional stations are placed in operation in various parts of the country. If later developments should favor the use of higher frequencies, the Commission will consider the facts at that time. In any event, the record of the hearing clearly indicates that this particular band offers the best solution of the allocation problem at this time. Therefore, the Commission is making available for regular high-frequency broadcast stations and educational stations the frequency band 42000 to 50000 kc, in which band 40 200-kc. channels are available. Adequate provision will be made for television service as pointed out in our statement on allocations accompanying Commission Order 67. The channels made available by Order 67 to FM broadcast stations, including the multiplexing of facsimile transmission simultaneously with aural broadcasting, are assigned to sei-vices as follows : Non-Commercial Educational Broadcast Stations : 42100 42500 42900 42300 42700 gh-Frequency Broadcast Stations : 43100 44900 46700 48500 43300 45100 46900 48700 43500 45300 47100 48900 43700 45500 47300 49100 43900 45700 47500 49300 44100 45900 47700 49500 44300 46100 47900 49700 44500 46300 48100 49900 44700 46500 48300 Under the foregoing allocation for FM broadcast stations, the same number of frequencies previously allocated to educational stations has been retained, the only change being that the band for such stations has been placed 1,000 kilocycles higher in the spectrum. This arrangement provides for educational channels in the regular high-frequency broadcast band and thus permits the same receiver to be used for the two services. The 1,000 kc. set aside in the lower part of the band allocated to commercial broadcast stations for educational stations not only places the educational stations on an entirely independent basis but also gives them the benefit of the developments in the service rendered by the commercial stations. The few existing non-commercial educational broadcast stations employ amplitude modulation. It is contemplated that they may continue so to operate with the same equipment in the new frequency band 42,000-43,000 kc. It is not contemplated, however, that applications for new educational broadcast stations proposing amplitude modulation will meet the Commission's requirements in the absence of a showing of special necessity for the use of amplitude modulation. The bands 25,000-27,000 kc. and 116,000118,000 kc. will not hereafter be assigned to FM domestic broadcasting. There are pending a number of applications for high-frequency broadcast stations on an experimental basis, which were filed pursuant to existing rules and regulations. None of these applications is sufficient for the authorization of a regular broadcast station on a full commercial basis nor are any of them sufficient for the limited experimental service to be authorized. Therefore, these applications wiU be dismissed, but without prejudice to the filing of new applications for either experimental or regular FM broadcast stations. Rules and regulations for both regular and experimental service will be promulgated by the Commission in the near future. It also follows that authorizations for existing high-frequency experimental broadcast stations which contemplate service to the public should be terminated not later than Jan. 1, 1941, without prejudice to the filing of new applications for either type of service. Applications for FM broadcast stations will be accepted by the Commission when the new rules and regulations for FM broadcast stations, including standards of good engineering practice, and application forms are issued. This will be done promptly. BROADCASTING • Broadcast Advertising June 1, 1940 • Page 19