Broadcasting (Oct 1931-Dec 1932)

Dr. Jolliffe Explains Allocation Standards Used bv Commission Radio Body's Annual Report Shows Applicants How to Determine Engineering Requisites Dr. Jolliffe WHYS A N D wherefores of the Federal Radio Commission's engineering methods of broadcast allocations, which have been something of an enigma to the industry, are defined for the first time in the annual report of the Commission, just made available. "Empirical standards for broadcast allocation" is the way Dr. C. B. Jolliffe, chief engineer, describes the analysis. It embraces the day and night mileage separations adopted as standard by the Commission, as well as all other available engineering data regarded as authentic. The material was compiled by Andrew D. Ring, senior engineer of the Broadcast Section, whose duties include the presentation of engineering testimony at hearings on broadcasting applications. Together with tables, charts and graphs, the analysis sets forth the "engineering yardstick" applied by the Commission to all broadcast applications raising engineering questions, Dr. Jolliffe said. He pointed out that practically all broadcasting application denials are based on engineering questions, yet very few applicants actually know that there are engineering objections at the time they tender their requests. "By following the empirical standards, station engineers and other prospective applicants should be enabled to determine in advance exactly what the engineering requisites are and thereby should eliminate much lost motion and expense," Dr. Jolliffe asserted. "These standards answer the hundreds of engineering questions put to the Engineering Division by interested parties." Moreover, declared the chief engineer, the standards set forth exactly what the Commission expects in the technical performance of stations. The yardstick gives the basis for determining just how the service of any given station measures up to the specifications set out in the rules and regulations. New Standards TO INSURE uniformity, it is brought out, it has been necessary to adopt many empirical standards of reception, interference, service area and the like that have not previously been published. In developing these standards, all sources of information now available have been used, and as more and more technical broadcast data are obtained these standards will necessarily change. Since many of the standards are also based on present day average receiving sets, average standards of listeners, present design of antennas, etc., they will be changed as the art progresses. The standards are based and averaged upon data obtained through evidence given at hearings by expert radio engineers; the experience of Commission engineers based upon personal experiences and observations in the field and on studies of reports and publications on the subject; averages of hundreds of field intensity measurements made by the Radio Division, Commerce Department; a study of interference reports made by the Radio Division; several complete surveys made of individual stations by Radio Division and other engineers with respect to service areas and interference; various published formulas on transmission; and the known characteristics of receiving sets. The problem most difficult to solve and at the same time the most important to consider with respect to service on a channel on which more than one station operates simultaneously at night is the "nuisance area" or interference range, the report states. The standards define this area as one over which interference may be caused to reception of other stations on the same frequency. A 1 kw. station has an average good service radius of approximately 40 miles and a nuisance radius of about 1,000 miles. A 1 kw. station located less than 1,000 miles from a second 1 kw. station will have mutual interference that will limit the good service radius to less than 40 miles. Interference to reception is defined as any spurious or extraneous sound accompanying reception, but as used in connection with the standards it refers to objectionable sounds present over 10 per cent of the time. Thus the good service area is defined as that in which satisfactory reception free from interference is obtained at least 90 per cent of the time. Classes of Service WITH respect to field intensities, the standards set forth that for good service, depending upon the noise level of the area to be served, such intensities are divided into three classes. In a business city, the signal should be 10 millivolts per meter, in a residential city, 2 millivolts per meter; and in rural areas, 0.5 millivolts per meter. For fair service, the signal is one-half of these values, and for poor service one-fourth. The figures were said to be subject to change if the noise level is unusual or fading is experienced. The study also defines standards governing average distances over which stations of various powers can be expected to give service, with the stations classified in the various categories of service. Geographical separation standards for stations on adjacent frequencies are defined in detail, as are the mileage separations, both day and night between stations on the same adjacent frequencies. A study of characteristics of many receiving sets reveals that the ratio necessary to prevent interference varies widely with different sets. The limit of common commercial broadcast receivers was found to lie within the ratios of 1 to 10 and 10 to 1. Old receivers with tubes of impaired emission, changed tuning, etc., will undoubtedly be less selective than the new receivers studied. Many reports received from listeners complaining of cross-talk which have been investigated disclosed that the separation is often greater than called for in the standards. It is recognized that absorption and other physical conditions vary widely throughout the country and that the tables may be conservative for certain areas, while in others, they give unnecessary protection from interference. This is taken into consideration in studying individual cases. The detailed analysis of the empirical standards, together with the graphs and charts, are all contained in the Commission's annual report, which may be procured from the Government Printing Office, Washington, for 15 cents. Radio Service Men Form an Institute Larger Audience Predicted as Chicago Movement Spreads LARGER audiences for broadcasting stations will result from the operation of the Institute of Radio Service Men, organized last summer with headquarters at 720 South Dearborn St., Chicago, according to Ken Hathaway, formerly technical editor of the Chicago Daily News. The purpose of the organization, said to be international in scope, is to provide a technical headquarters for radio service men as the Institute of Radio Engineers does for engineers. "While broadcasters have provided consistently high grade transmission, the number of listeners is below what it should be, principally because with the rapid expansion of the radio industry the importance of the service branch has been overlooked," Mr. Hathaway said. The institute is the outgrowth of a successful experiment conducted last winter in Chicago, Mr. Hathaway explained. Some 330 radio service men met twice monthly to discuss mutual problems of their vocation. One of the principal topics was "What a Service Man Should Know About Broadcasting." Similar programs have been started this winter in Chicago and New York, and other cities are to be added as the interest and gathering of radio service men warrants. Back on the Air WJBL, Decatur, 111., whose transmitter was destroyed by fire Nov. 20, has rebuilt the station with composite equipment and was scheduled to be back on the air Dec. 10. WWV to Broadcast Frequency Signals Transmitters and Receivers Can be Checked Shortly A NEW SCHEDULE of standard frequency radio signals will eminate from WWV, of the U. S. Bureau of Standards in Washington, covering January, February and March transmissions for use of all kinds of radio stations in adjusting transmitters to exact frequency and by the public in calibrating receiving apparatus, according to an-, nouncement by the Bureau. All transmissions are on 5,000 kilocycles and can be heard and utilized by stations equipped for continuous-wave reception within range of WWV. The accuracy of the transmitted frequency is at all times better than one part in 1,000,000. Signals are by radiotelegraphy. They will be given continuously from 2 to 4 p. m., and from 8 to 10 p. m., EST, every Tuesday. The dates are Jan. 5, 12, 19 and 26; Feb. 2, 9, 16 and 23; and March 1, 8, 15, 22 and 29. The transmissions will consist mainly of continuous, unkeyed carrier frequency, giving a continuous whistle in the phones when received with an oscillatory receiving set. The first five minutes of the transmission will consist of the general call (CQD-WWV) and announcement of the frequency. The frequency and the call letters of the WWV are to be given every 10 minutes thereafter. Information on how to receive and utilize the signals may be obtained by addressing a request to the Bureau of Standards, Washington, D. C. From the 5,000 kilocycles any apparatus may be given as complete a frequency calibration as desired by the method of harmonics. A statement from the Bureau says that it "is desirous of receiving reports on these transmissions, especially because radio transmission phenomena change with the season of the year. The data desired are approximate field intensity, fading and the suitability of the transmissions for frequency measurements. It is suggested that in reporting upon field intensities for these transmissions, the following designations be used where field intensity measurement apparatus is not at hand; (1) hardly perceptible, unreadable; (2) weak, readable now and then; (3) fairly good, readable with difficulty; (4) good, readable; (5) very good, perfectly readable. A statement as to whether fading is present or not is desired, and if so, its charactei*istics, such as whether slow of rapid and time between peaks or signal intensity. Statements as to type of receiving set used in reporting on the transmissions and the type of antenna used are likewise desired. The Bureau would also appreciate reports on the use of the transmissions for purposes of frequency measurement or control." THE INSTITUTE of Wireless Technology moved to more commodious quarters at 72 Oxford Street, London, on Dec. 1. Page 24 BROADCASTING • December 15, 1931