Sec. 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 Sec. 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 
Sec. 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:

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    (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 Sec. 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 Sec. 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 
Sec. 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     .967
------------------------------------------------------------------------


[28 0 FR 13574 , Dec. 14, 1963, as amended at  49 FR 43962 , Nov. 1, 1984;  56 FR 64868 , Dec. 12, 1991]

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