Broadcasting (July - Dec 1936)

WAVE WAVES A WAVING WAND! i.= WAVE adver SomC ,°f Jleen getiSg lately are tisers have been & enal-and nothing short ^ P any programs m if you're Pl^gc^ JU you inthis area, we ask on y ^ magic? vestigate them . ■ ■ q( u9ing a of course-xt s the ett ^ both station tha^urerl?etorks-to an Red and Blue ' rof ed in Kenaudience con"^ FREE & PETERS, INC. ing 10 kc. factor rather than the 10 kc. cross talk. At lesser separation than 10 kc, this factor becomes increasingly worse and intolerably limiting. Improved receiver selectivity existing today could be used to advantage either in reducing separation of stations in the same community to 40 kc. or by maintaining the 50 kc. separation and permitting higher field intensities. From the result of the clear channel survey conducted by the FCC, the latter alternative is obviously preferable, since it gives improved service in rural areas without causing objectionable interference close to the transmitter. Mr. Van Dyck said: Revision of Tables "IN SPITE of the fact that the broadcast system determination of overall performance involves consideration of numerous factors, it is possible to set up tables showing relations between essential factors, which will take satisfactory account of the great majoritv of allocation problems. There will of course be special cases where general, average condition tables are not suitable, but in the main, and used with discretion, averaged tables can be highly useful. "We therefore believe that suitable tables may be set up if appropriate standards are utilized for their preparation. The standards must include those for wave propagation, includine factors of attenuation, transmitter power, antenna efficiency and directivity, and those for receiver performance including selectivity, fidelity, per IN ST. LOUIS 5 OFFERS SPONSORS DAYTIME COVERAGE INCLUDING A POPULATION OF ^ ^fl^r This is the total population of territory rcc J rng one-half millivolt service or better bi ased on measurements made by Jonslty & Bailey. centage of receivers which may experience interference, and the lower limit of field intensity from desired station necessary to protect. "It is believed that the frequency separation tables now used by the Commission can be reviewed and revised with advantage, in view of the additional and later data submitted herein, which was not available at the time when the present tables were set up." NBC Research Chief CITES FIELD SURVEYS SUPPLEMENTING the case presented by NBC, Charles W. Horn, chief of research and development for the network, presented a statement Oct. 15 describing the comprehensive studies made by NBC in connection with propagation. He made three recommendations: (1) an additional classification calling for 50 millivolts for metropolitan areas as a minimum signal necessary for good service (as against 10 to 25 millivolts provided in existing standards); (2) that the power measurements of stations be made by the direct method of antenna measurements, and (3) that field strength measurements be made of all stations. Introdueing a series of charts and graphs and other technical calculations, Mr. Horn brought out that experience during the last several years has removed a great deal of guesswork from station measuring data. He presented a map showing the ground conductivities in areas in which NBC had made measurements of 60 stations in different cities. Based on these studies, Mr. Horn said that interference due to natural static varies with the seasons and is more prevalent in the southern part of the United States, especially in the summer. In the more built-up sections, particularly the larger cities, much static is caused by electrical devices. Diathermy machines lately have contributed to this interference. He pointed to efforts made by large industrial concerns to minimize it. Minimum Signal Intensities COVERING signal intensity necessary to render satisfactory service in various types of communities, Mr. Horn brought out that the standards published by the FCC engineering division have been observed for some years. These require 10 millivolts for good reception in cities, 2 millivolts in residence sections and .5 millivolts in rural localities. He said these figures are based on the fact that electrical noises are greater in cities than in residential and rural parts of the country. While they have proven quite satisfactory except in the case of metropolitan areas, he said that experience indicated that another factor should be added to take care of metropolitan areas. As a consequence, he recommended the signal intensity be not less than 50 millivolts. A discussion of sky wave propagation with relation to sunspot cycles and the Heaviside Layer was given by Mr. Horn. Seasonal variations, he said, have a marked effect upon the sky wave, which furnishes secondary service, but has little effect upon the ground wave. The net results of these studies, he said, has been to show that the best service rendered the public is in the primary service areas which are less effected by atmospheric and cosmic changes. Citing the Radio Commission map of 1933 covering calculated night primary coverage of all broadcast stations, he said this showed that out of a total of 119,636,708 people, the population that resided within the primary coverage of the broadcasting stations was 76,662,000 or 64.2%. There were approximately 43,000,000 people living within the secondary area or 35.8% of the: total. Receivers in this secondary area, which covers 70.6% of the total area of the country, are' solely dependent upon the sky wave; or secondary area signals of sta-l tions which have sufficient power and are free from interference. While this map is dated Decern-' ber 1933, Mr. Horn said that there has been relatively little change in the number of stations since that, time and while some of these stations may have increased their, power they have not materially! increased their primary service area because of the fading limitations. "Long distance transmission or service to the secondary area," Mr. Horn continued, "is possible only on channels which are free from interference. The system we have adopted, that of using high power on clear channels and lower power on shared channels, is universally recognized and is in use in Europe as well as in other parts of the world." Synchronization Factors DISCUSSING synchronization, of which he was one of the early advocates, Mr. Horn said the belief exists in some quarters that stations can be synchronized and broadcast different programs. He declared, however, that this does not hold true until the separation between the stations is great enough to provide a signal ratio: of 20 to 1, desired to undesired. Synchronizing a whole chain of stations is at present impractical, both technically and economically, he added, stating that synchronization is still in an experimental stage. Mr. Horn described in detail the MACON, G A . WKZO KALAMAZOO "Western Michigan's Premier Station" Station KSD— St. Louis Post-Dispatch POST-DISPATCH BUILDING, ST. LOUIS, MO. FREE 8t PETERS, Inc., National Advertising Representative New York Chicago Detroit San Francisco Los Angeles Page 66 • November I, 1936 BROADCASTING • Broadcast Advertising