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Code of Federal Regulations (Last Updated: July 5, 2024) |
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Title 47 - Telecommunication |
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Chapter I - Federal Communications Commission |
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SubChapter C - Broadcast Radio Services |
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Part 73 - Radio Broadcast Services |
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Subpart A - AM Broadcast Stations |
§ 73.187 - Limitation on daytime radiation.
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§ 73.187 Limitation on daytime radiation.
(a)
(1) Except as otherwise provided in paragraphs (a)(2) and (3) of this section, no authorization will be granted for a Class B or Class D station on a frequency specified in § 73.25 if the proposed operation would radiate during the period of critical hours (the two hours after local sunrise and the two hours before local sunset) toward any point on the 0.1 mV/m contour of a co-channel U.S. Class A station, at or below the pertinent vertical angle determined from Curve 2 of Figure 6a of § 73.190, values in excess of those obtained as provided in paragraph (b) of this section.
(2) The limitation set forth in paragraph (a)(1) of this section shall not apply in the following cases:
(i) Any Class B or Class D operation authorized before November 30, 1959; or
(ii) For Class B and Class D stations authorized before November 30, 1959, subsequent changes of facilities which do not involve a change in frequency, an increase in radiation toward any point on the 0.1 mV/m contour of a co-channel U.S. Class A station, or the move of transmitter site materially closer to the 0.1 mV/m contour of such Class A station.
(3) A Class B or Class D station authorized before November 30, 1959, and subsequently authorized to increase daytime radiation in any direction toward the 0.1 mV/m contour of a co-channel U.S. Class A station (without a change in frequency or a move of transmitter site materially closer to such contour), may not, during the two hours after local sunrise or the two hours before local sunset, radiate in such directions a value exceeding the higher of:
(i) The value radiated in such directions with facilities last authorized before November 30, 1959, or
(ii) The limitation specified in paragraph (a)(1) of this section.
(b) To obtain the maximum permissible radiation for a Class B or Class D station on a given frequency from 640 through 990 kHz, multiply the radiation value obtained for the given distance and azimuth from the 500 kHz chart (Figure 9 of § 73.190) by the appropriate interpolation factor shown in the K500 column of paragraph (c) of this section; and multiply the radiation value obtained for the given distance and azimuth from the 1000 kHz chart (Figure 10 of § 73.190) by the appropriate interpolation factor shown in the K1000 column of paragraph (c) of this section. Add the two products thus obtained; the result is the maximum radiation value applicable to the Class B or Class D station in the pertinent directions. For frequencies from 1010 to 1580 kHz, obtain in a similar manner the proper radiation values from the 1000 and 1600 kHz charts (Figures 10 and 11 of § 73.190), multiply each of these values by the appropriate interpolation factors in the K′1000 and K′1600 columns in paragraph (c) of this section, and add the products.
(c) Interpolation factors.
(1) Frequencies below 1000 kHz.
fkHz K500 K1000 640 0.720 0.280 650 0.700 0.300 660 0.680 0.320 670 0.660 0.340 680 0.640 0.360 690 0.620 0.380 700 0.600 0.400 710 0.580 0.420 720 0.560 0.440 730 0.540 0.460 740 0.520 0.480 750 0.500 0.500 760 0.480 0.520 770 0.460 0.540 780 0.440 0.560 800 0.400 0.600 810 0.380 0.620 820 0.360 0.640 830 0.340 0.660 840 0.320 0.680 850 0.300 0.700 860 0.280 0.720 870 0.260 0.740 880 0.240 0.760 890 0.220 0.780 900 0.200 0.800 940 0.120 0.880 990 0.020 0.980 (2) Frequencies above 1000 kHz.
f′kHz K′1000 K′1600 1010 0.983 0.017 1020 0.967 0.033 1030 0.950 0.050 1040 0.933 0.067 1050 0.917 0.083 1060 0.900 0.100 1070 0.883 0.117 1080 0.867 0.133 1090 0.850 0.150 1100 0.833 0.167 1110 0.817 0.183 1120 0.800 0.200 1130 0.783 0.217 1140 0.767 0.233 1160 0.733 0.267 1170 0.717 0.283 1180 0.700 0.300 1190 0.683 0.317 1200 0.667 0.333 1210 0.650 0.350 1220 0.633 0.367 1500 0.167 0.833 1510 0.150 0.850 1520 0.133 0.867 1530 0.117 0.883 1540 0.100 0.900 1550 0.083 0.917 1560 0.067 0.933 1570 0.050 0.950 1580 0.033 0.967 [28 FR 13574, Dec. 14, 1963, as amended at 49 FR 43962, Nov. 1, 1984; 56 FR 64868, Dec. 12, 1991]