Page:United States Statutes at Large Volume 55 Part 2.djvu/143

 TREATIES Post, pp. 1026, 1027. Post, p. 1028. Post, p. 1027. Post. p. 1026. Pot, p. 1028. (b) By reference to the propagation curves in Appendices IV and V, or (c) By reference to the distance tables set forth in Appendix VI. 4. Actual proof of existence or absence of objectionable interference. The existence or absence of objectionable interference may be proved by field intensity measurements or recordings made with suitable apparatus, duly calibrated, by Government engineers or other engineers as may be mutually acceptable to the Governments con- cerned. Such field intensity measurements shall be made in the manner and for the periods of time mutually agreed upon by the Governments concerned. The contracting Governments agree to facilitate the making of the measurements by requiring the stations involved to remain silent or operate in the manner deemed necessary, and at such times as not to interrupt regular schedules. 5. Proof based on propagation curves and distance tables. (a) Sky wave curves. In computing the distance to the 50 per cent sky wave field intensity contour of a Class I station of a given power, and also in computing the 10 percent sky wave field intensity of an alleged interfering station, of any class and given power, at a specified distance, use may be made of the appropriate graphs set forth in Appendix V, entitled "Average Sky Wave Field Intensity Corresponding to the Second Hour after Sunset in the Recording Station, 100 Millivolt per Meter at One Mile (161 at one kilometer)". (b) Ground wave curves. The distance to any specified ground wave field intensity contour may be determined from appropriate ground wave curves plotted for the frequency under consideration and the conductivity and dielectric constant of the earth between the station and desired contour. The frequency and the conductivity of the earth must be considered in every case and where the distance is great due allowance must be made for loss due to curvature of the earth. A family of curves is necessary for this purpose. A graph for a conductivity of 10-' is set forth in Appendix IV, entitled "Ground Wave Field Intensity vs. Distance for One Kilowatt Radiated From Short Antenna". Three frequencies in the standard broadcast band are given. For other frequencies and soil conditions (conductivity and dielectric constant) other curves are required. A conductivity of 10-1 ' is considered average and is used throughout in determining the ground wave value for computing the mileage separation tables. (c) Distance tables. Table I shows the required day separation in miles between broadcast stations on the same channel. Table II gives the required distance in miles from the boundary of a country in which a Class I-A station is located for the daytime operation of a Class II station on the same channel in another country. Table III gives the required separation in miles between broadcast stations on adjacent channels during both daytime and nighttime. Table IV gives the required night separation in miles between broadcast stations operating on the same channel. The assumed conditions of operation are given in Appendix VI. 1014 [55 STAT.

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