Television digest with electronic reports (Jan-Dec 1956)

49. On November 9, 1955, Scharfeld and Baron of Washington, D. C. filed a petition proposing that channel assignments be made on the basis of individual applications rather than under a fixed Table of Assignments. The Commission has given careful consideration to this proposal, but is not persuaded that it virould be in the public interest to abandon the Table of Assignments at this time. Before the Sixth Report and Order was adopted the Commission considered proposals to assign television channels on the basis of individual applications. It was decided, however, for reasons set out in that document, that it would be preferable to establish a table of assignments subject to modification through rule making proceedings. Although not all the reasons given at that time are applicable now to the full extent they were in 1952, when a large backlog of applications would have rendered the application basis almost unmanageable, the Commission hesitates to discard the Table and thei’eby incur delays which may occur in cases where applications propose conflicting assignments. Moreover, retention of the present system of fixed assignments subject to modification in rule making proceedings is desirable for implementation of the policies adopted in this Report and Order. 50. In our Further Report and Order adopted in this proceeding on November 30, 1955, the Commission gave notive that it would consider herein the petition which Northern Pacific TV Corporation of Spokane, Washington, filed on November 17, 1954, requesting the amendment of Section 3.614(b) of the Rules so as to permit stations operating on Channels 2-6 in Zone II to operate with maximum power of 100 kw irrespective of antenna height. On the basis of careful consideration of this proposal the The accompanying Tables, which have been drawn up on the basis of new propagation data,' provide the basis for determining the Grade B service contours of television stations in the presence of noise and co-channel interference. In order that rapid determinations may be reached, an abbreviated method is to be used in employing the Tables. In constructing the Tables it has been assumed that a contour wihch reflects the effect of each interfering station separately will approximate that derived from computing the simultaneous effect of several interfering signals since the interference from the nearest station will predominate. The Tables are based on new minimum local field intensities of 35, 44, and 63 dbu in the presence of noise for low VHF, high VHF and UHF, respectively, and on a maximum receiving antenna discrimination of 6 db for VHF and 13 db for UHF. These new figures are employed in light of experience and improvement in the art since the Sixth Report and Order. They represent the following changes from the values employed at the time of the Sixth Report and Order. A 6 db improvement in the receiver noise figure for low VHF, a 4 db improvement in the receiver noise figure and a 3 db improvement in the receiving antenna gain for high VHF, and a 5 db improvement in the receiver noise figure and a 2 db improvement in transmission line loss for UHF. Maximum power for VHF stations, 1,000 kw for UHF stations and 1,000 foot transmitting antenna heights have been assumed in compiling the Tables. All of the data underlying the Tables are based on the foregoing assumptions and on 90% service time probability. Table I gives the distance of a television station’s signal as limited by noise for 50% and lO'/c of the locations for the low band VHF, high band VHF and UHF in the presence of noise only. Table II gives the minimum spacing between co-channel stations in order that their G)-ade B contoui's will be lim •' See “Present Knowledge of Propagation In the VHP and UHP' TV Bunds, ” W. C. Boese and H. Fine TBR 2.4.15., Noveintjer 15, 1955. Commission has concluded that it would not serve the public interest to remove the maximum limitations set out in the present rules at the present time. The basic considerations which apply here are similar to those already discussed in paragraphs 43 and 44, above, relating to the proposal to increase the antenna height at which VHF stations in Zone I are permitted to use maximum power. 51. In accordance with the decision reached on the proposal to increase the maximum power of UHF stations to 5000 kilowatts, discussed in paragraph 41 above, IT IS ORDERED, That effective August 1, 1956, Part 3 of the Commission’s Rules is amended as follows: A. Section 3.614(b) is amended by deleting in the Table the expression “30 dbk (1000 kw)” and substituting therefor “37 dbk (5000 kw).” B. Section 3.699 is amended by the deletion of Figures 3 and 4 and the substitution therefor of the attached Figures 3 and 4. 52. Authority for the foregoing amendment is contained in Sections 303(a), (b), (c), (e), (f), (g), (h) and (r) and 4(i) of the Communications Act of 1934, as amended. 53. In accordance with the conclusions reached herein, IT IS ORDERED, That this proceeding IS TERMINATED, including that portion of this proceeding concerning amendment of the rules governing maximum antenna heights and powers in Zone I, which was formerly considered under Docket No. 11181. FEDERAL COMMUNICATIONS COMMISSION Mary Jane Morris, Secretary Adopted June 25, 1956. Released June 26, 1956. Note: Rules changes herein will be included in Amendment No. 3-16. IX A ited by noise only. When stations are spaced at distances less than those indicated, their service areas will be limited by the resulting interference. Table III gives the point, on a direct line between stations, at which Grade B service will be limited by cochannel interference on the basis of the single station method of computation.® Linear interpolations may be used for distances between those listed. Table IV gives the radii of the interfering signals which reduce the 70% noise limitation to an overall limitation of 50%. The following example explains how the Tables should be used: Consider three co-channel TV stations in the low VHF band: Stations A, B and C (See Figure 1). The stations are offset. Station A is 180 miles from Station B and 225 miles from Station C. Station B is 290 miles from Station C. The problem is to determine the limitations of the Grade B contour of Station A in the presence of noise and the interfering signals from Stations B and C. From Table I draw the 50% and 70% location contours as limited by noise. These are found to be circles of 78 and 71 mile radii, respectively. The contour limitation of Station A in the direction of Station B can be obtained by finding from Table III the distance to the interference free Grade B contour di for a spacing of 180 miles for low VHF stations operating on an offset basis. This contour is found to fall 50 miles from Station A, and this point should be plotted on a line between Stations A and B. Two additional points should now be located to deter The figures in the Table were computed by obtaining the point on a line between stations at which the desired field exceeds the undesired by the required ratio. This does not give the precise point at which Grade B service is limited since receiver noise factor is not considered. In dealing with stations in the low VHP band, it would be necessary to consider non-offset stations as far removed as 650 miles in order to take noise also into account. When using the simple method employed here for the spaclngs usually encountered the results may place the service contours from 1 to 4 miles beyond the actual figure that will be obtained if noise were also taken into account. Nevertheless, we believe the suggested method affords results of sufficient accuracy for present purposes. 8