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:

   (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  K[500]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 K[1000]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 K^500 K^1000
   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]