Broadcasting Telecasting (Apr - Jun 1952)

UHF band. At the hearing on the general issues, testimony was offered that these separations could be reduced considerably by utilizing offset carrier operation. Evidence was also offered that more television service could be made available to the country if the separation objective were reduced to 150 miles for VHF channels. The Commission has carefully considered the above evidence and has concluded that some reduction in co-channel separation is possible because of the improvements which result from offset carrier operation. It is not deemed advisable to effectuate a reduction to 150 mile VHF separation as suggested at the hearing. In the first place, the evidence upon which the 150 mile separation is based is the theoretical computations of what coverage can be achieved. On the basis of the evidence in the record, it is clear that considerations of terrain and other propagation factors will materially affect many of the theoretical computations. In the second place, much of the propagation data — although the best available— upon which the Commission relies is necessarily quite meager. Postponing a decision in these proceedings would not materially aid this problem since it has been the Commission's experience that substantial amounts of propagation data do not become available until stations are authorized on a regular basis. Hence, the Commission is faced with the practical problem that if it postpones assigning stations until sufficient propagation data are available, such data may never become available, while on the other hand if stations are assigned before sufficient propagation data are assembled, more interference may result in actual operation than was anticipated. In the Commission's view, the best method of handling this problem is to assign stations as soon as a reasonably sufficient amount of data is accumulated, but in doing so assignments should not be made on the barest minimum separation which exact calculations would indicate. Instead, a safety factor should be included. In this way. if as a result of actual experience more interference results than was indicated by the earlier calculations, the safety factor will prevent extensive damage to overall service. If actual experience shows that the amount of interference is approximately that predicted by the calculations, then the rules and standards can be amended to reflect the new data. In the Commission's experience, it is much easier as a practical matter to reduce station separations which are somewhat larger than were originally thought to be necessary than it is to increase separations which are smaller than were originally thought to be necessary. 110. In determining minimum cochannel separations we must consider a number of factors. The geographical distribution of the people and cities of the United States does not lend itself to a simple rule for the spacing of stations. The northeastern portion of the United States is generally charac terized by higher population density and closer spacing of cities than the other portions of the country. See Appendix A. 111. Recognition must also be given to the fact that the mileages set for co-channel spacings determine the size of the interferencefree service area of nearby cochannel stations. It is important to note that we are referring here not to Grade A service but to the more extensive Grade B service. As spacings in the order of 140-250 miles are reduced by 10 miles the interference free service area is reduced by 2-3 miles in the direction in which stations face each other. Accordingly, reductions in Grade B service resulting from reduced separations deprive the rural areas and the less sparsely settled areas of television service. To the extent we do this in the "VHF, we lose one of the benefits of that portion of the spectrum, the wide area coverage possible. 112. We have also considered the import of minimum spacings on the policy we have adopted herein with respect to the use of greater heights and higher powers. As greater antenna heights and higher powers are used, the greater is the need for wider separations; with smaller separations, in the direction of the co-channel station, the potential gain from greater heights and higher powers would be lost. We do not wish to negate the policy of trying to obtain wide coverage by the use of high antenna heights; neither do we wish to create excessive interference by permitting operation with high power at small spacings. 113. Finally we have given consideration to the need for a safety factor in view of the incomplete nature of available propagation data. Where the pros and cons hang in even balance we deem it highly desirable if not imperative to tip the scales in favor of wider separations. 114. The Commission in the Third Notice provided the following minimum co-channel assignment spacings between cities: VHF — 180 miles UHF — 165 miles Actually, however, it was not intended that all requests for additional assignments should be granted solely because they met the minima provided for in the Third Notice. The Third Notice stated: In each case, the above figures are minimum separations. Greater separations are utilized in the sparsely settled areas of the country in order to secure a maximum amount of service. In addition, greater separations are also utilized in Gulf Coast areas and in other areas where high levels of tropospheric propagation may be expected. This should be kept in mind by persons desiring to suggest changes in the Table of Assignments. (Emphasis added.) 115. Moreover, examination of the Table of Assignments proposed in the Third Notice makes it clear that the 180 mile VHF co-channel separation and the 165 mile UHF co-channel separation were not intended to be the minimum assignment spacing throughout the country. These minimum spacings were intended to be used and were used only in those portions of the country where narrower spacings are appropriate, particularly in the northeastern part of the United States. Upon review of the whole record we adhere to the concept that in the less densely settled areas of the country wide separations must be maintained. The minimum VHF co-channel spacing utilized in the Third Notice in such areas of the country was 190 miles. We adopt this spacing as the appropriate minimum VHF spacing in areas which have a relatively lower population density or where large cities are more widely separated. See Appendix A. For if we were to permit stations at close separations in such areas, we would deprive persons residing in the interference areas between such stations of television service since there generally do not exist other cities of sufficient magnitude in this interference area capable of supporting stations on other channels which could serve the area. 116. A different situation, however, exists where there is a higher density of population and concentration of cities. Because of the concentration of cities, the provision for lower minimum spacings in such an area will not have the tendency of depriving residents of the area of television service, since there would be an overlapping of service contours of stations on different channels located in the interference areas. 117. Analysis of population density and distribution of cities establishes the existence of one large contiguous area where there is a substantially higher density of population and concentration of cities compared to all other contiguous areas of comparable size. See Appendix A. We believe the record in the general portion of the hearing supports the conclusion that lower separations in this area are warranted. 118. We have called this area Zone I. It consists of that portion of the United States located within the confines of the following lines drawn on the United States Albers Equal Area Projection Map, (based on standard parallels 29%° and 45%° North American datum): Beginning at the most easterly point on the state boundary line between North Carolina and Virginia; thence in a straight line to a point at the junction of the Ohio, Kentucky, West Virginia State boundary lines, thence westerly along the southern boundary lines of the States of Ohio, Indiana and Illinois to a point at the junction of the Illinois, Kentucky and Missouri State boundary lines; thence northerly along the west boundary line of the State of Illinois to a point at the junction of the Illinois, Iowa and Wisconsin State boundary lines ; thence easterly along the northern state boundary lines of Illinois to the 90th meridian; thence north along this meridian to the 43.5° parallel; thence east along this parallel to the 71st meridian; thence in a straight line to the intersection of the 69th meridian and the 45th parallel; thence east along the 45th parallel to the Atlantic Ocean. When any of the above lines pass through a city the city shall be considered to be located in Zone I. A map of Zone I is included in the Rules adopted herein. 119. In establishing the boundaries of Zone I we have included within the Zone portions of some states that, as a whole, have relatively low population densities and relatively few large cities. The portions we have included, are, however, relatively more populous and have a greater number of large cities than the other portions of the same states and they are all contiguous to the general area with a higher density of population and concentrated cities. For these reasons we believe their inclusion in Zone I is warranted. 120. Upon consideration of the whole record, we have determined that the minimum co-channel assignment spacing in Zone I shall be 170 miles in the VHF and 155 miles in the UHF.25 This constitutes a reduction of 10 miles in the minimum assignment separation proposed in the Third Notice, but is the same as the minimum facilities separations provided for in the Third Notice. We find no basis for going below the 170 and 155 mile figures proposed as the minima in the Third Notice. 121. As we have pointed out in the Third Notice, in certain areas of the country, particularly the Gulf Coast area, high levels of tropospheric propagation may be expected. In such areas greater separations are necessary to compensate for the reduction in service areas that is caused by the interference resulting from the high level of tropospheric propagation. We have carefully re-examined the record and the comments that have been filed pursuant to the Third Notice and we have determined that only the Gulf Coast area should, by rule, be treated differently from other areas which may be affected by a high level of tropospheric propagation. In reaching this conclusion we are aware that wide separations will have to be maintained in other areas as well to protect against the effects of high levels of tropospheric propagation. We believe, however, that these situations can be considered on a case-to-case basis, and we have attempted to take care of this problem on such a basis in establishing the Table of Assignments in this proceeding. 122. We have designated the Gulf Coast area as Zone III. Zone III consists of that portion of the United States located south of a line, drawn on the United States Albers Equal Area Projection Map, (based on standard parallels 29%° and 45% ° North American datum), beginning at a point on the east coast of Georgia and the 31st parallel and ending at the United States-Mexico border, consisting of arcs drawn with a 150 mile radius from the following specified points : North Latitude West Longitude a) 29° 40' 83° 24' b) 30° 07' 84° 12' c) 30° 31' 86° 30' d) 30° 48' 87° 58' 30" e) 30° 23' 90° 12' f) 30° 04' 30" 93° 19' g) 29° 46' 95° 05' h) 28° 43' 96° 39' 30" i) 27° 52' 30" 97° 32' When any of the above lines pass through a city, the city shall be 25 We recognize that a few existing operations do not comply with the minimum separations set forth above. It has not been possible to remove these cases without unwarranted dislocation. BROADCASTING • Telecasting April 14, 1952 Part II Final TV Report • Page 23