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                            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[min]kHz                     K[min]1000  K[min]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]