Television digest with AM-FM reports (Jan-Dec 1951)

television service, as far as possible, to all people of the United States and to provide a fair, efficient and equitable distribution of television broadcast stations to the several states and communities. The Commission has set forth below the principles, in terms of priority, which form the basis of the Table of Assignments. These priorities are as follows: Priority No. 1 — To provide at least one television service to all parts of the United States. Priority No. 2 — To provide each community with at least one television broadcast station. Priority No. 3 — To provide a choice of at least two television services to all parts of the United States. Priority No. 4 — To provide each community with at least two television broadcast stations. Priority No. 5 — Any channels which remain unassigned under the foregoing priorities will be assigned to the various communities depending on the size of the population of each community, the geographical location of such community, and the number of television services available to such community from television stations located in other communities. B. Changes in Table 1. A channel assigned to a community in the Commission’s Table of Television Assignments shall be available, without the necessity of rule making proceedings, to any other community located within 16 miles of the assigned community provided the minimum separations set forth in paragraphs “E” and “G” herein are maintained.' 2. Upon adoption in the instant proceedings of the Table of Asssignments, said Table shall not be subject to amendment on petition for a period of one year from the effective date of the Commission’s final order amending said Table. Upon the expiration of said one year period the Commission will consider petitions filed during said period requesting changes in the Table. Thereafter, where the Commission has conducted a rule making proceeding in which it amended or refused to amend said Table, no petition concerning the amendment granted or denied may be filed within one year after the effective date of the Commission’s final order amending or refusing to amend said Table.® 3. Except as provided for in Paragraphs “II Al” and “II Bl” above, no application for a television station in a community specified in the Commission’s Table will be accepted for filing if said application requests a channel which is not contained in the Table. Persons desiring to apply for a channel not specified in the Table must first secure an amendment thereof through appropriate rule making proceedings. Petitions proposing changes in the Table must show the extent to which changes conform to the priorities listed in subparagraph “II Al” above, based upon stations operating in accordance with the Table of Assignments and employing the maximum power specified in subparagraph “D2” herein. C. Grades of Service* * In its Notice of Further Proposed Rule Making issued on July 11, 1949, the Commission proposed to classify tele < In d?>termining separations between cities for the purpose of (his provision, the city mileage separations set forth in the publication of the U. S. Department of Commerce entitled ‘‘Airline Distances between Cities in the United States'* shall be utilized. Where cities are not listed in the above publication, separations shall be computed on the basis of the distance between the main post offices in the respective cities. ■'* In applying this provision, each area specified in the Table shall be considered separately so that the provision is applicable only if the Commission’s action related to an assignment for the area in question. For example, if the Commission denies a petition for rule making requesting that television channel X be removed from City B to City A, no petition for rule making to move a channel from City B to City A will be eligible for filing for one year, even though the request may be to remove Channel Y or Channel Z from City B. However, a petition may be filed before the expiration of one year to remove a channel from City C to City A. * The Commission proposes the use of iso-service contours which express service in terms of the ratio between desired and undesired signal in decibels, or the minimum required signal levels in decibels above one microvolt per meter. This has been done in order to facilitate computation of service and interference field strengths. Likewise, the same terms may be carried over to the output of the transmitter, transmission line loss and antenna gain. This has the advantage of using the same unit throughout the service whether in the transmitting equipment or in the vision broadcast service into three grades of service. In the Commission’s opinion, there is no need for more than two grades of service. Grade A service is so specified that a quality acceptable to the median observer is expected to be available for at least 90% of the time at the best 70% of receiver locations at the outer limits of this service. In the case of Grade B service the figures are 90% of the time and 50% of the locations.’ The field strengths and interference ratios are as follows: 1. Required median field strengths in db above 1 uv/m: Grade of Service A B Channels 2-6 68 db 47 db Channels 7-13 71 db 56 db Channels H-83 74 db 64 db 2. Permissible co-channel ratios in db of median desired field strengths to 10% undesired field strengths: Grade of Channels 2-13 Channels H-8 3 Serviee Non-offset Offset Non-offset Offset A 61 db 34 db 63 db 36 db B 45 db 28 db 45 db 28 db 3. Permissible adjacent channel ratios in db of median desired and undesired field strengths: Grade of Service Channels 2-83 A Odb B Odb 4. a. Prediction of Service Areas and Interference Methods for describing service areas and interference are set forth in Appendix B. The methods therein described include the propagation of radio waves through the lower atmosphere only. These propagation charts are based on an extensive number of measurements made at various locations over a long period of time. It is recognized that these charts may have to be revised from time to time as more measurements are made, and interested persons are encouraged to make as many measurements as possible and submit them to the Commission. The Commission is satisfied that on the basis of the data presently available to it the data underlying the propagation charts are sufficient to afford an adequate statistical basis for describing field intensities under average conditions, but it is expected that there may be substantial variations in individual areas. b. Long Distance Skywave Interference It is also realized that propagation to distances of the order of 500 to 1500 miles via the sporadic E layer and to distances beyond via the F2 layer may occur in certain of the channels. However, since such interference may occur over extremely large distances, it is not possible to protect stations against such interference unless operation on such channels is limited to one or at the best a few stations. In order to provide stations for the various communities, the Commission has determined that the overall public interest is better served by not protecting television broadcast stations against this tjqie of interference. D. Classes of Stations The Commission’s Notice of Further Proposed Rule Making issued July 11, 1949, provided for three classes of stations, i.e., community, metropolitan and rural stations. During the hearings on the General Issues relatively little comment was offered concerning the proposed classi field and has the additional advantage that a decibel of power added at the transmitter results in a decibel of increased field strength. In order to place these matters on a related basis, the decibels with respect to transmitter power and antenna gain as well as field strength must be expressed as decibels with reference to some given level. Field strength is expressed either in decibels above an undesired signal or decibels above a reference level which has been chosen as one microvolt per meter. A convenient reference level of transmitter power is 1 kilowatt. The propagation charts attached to Appendix B and identified as "Appendix V, Figures 1-4" are based upon the radiation in the equatorial plane of a half wave dipole antenna having an effective radiated power of one kilowatt. Antenna gain is expressed as the ratio in db of the maximum radiation from the antenna to the radiation in the equatorial plane of a half wave dipole with equal power input. ^ For the specialized case that exists in the case of adjacent channel interference, see Paragraph "II E2" below. 8