§  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 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]