49:(at sunset) or vice versa (at sunrise). This can cause radio stations to be picked up much farther away, possibly causing interference with other stations on the same frequency or adjacent frequencies. Usually stations operating under the restrictions of Critical Hours must sign off the air between the end of the evening critical hours and the beginning of the morning critical hours. In effect, permission to operate during critical hours gives daytime-only stations a few more hours in their broadcast day. This is especially important in autumn and winter, when these stations might otherwise need to be off the air during the important morning and afternoon drive times, when AM radio listening is at its highest.
38:
distinguish them from the domestically defined critical hours. Canadian restricted hours is that time from sunrise to one and one-half hours after sunrise, and from one and one-half hours before sunset until sunset, local time. U.S. stations operate with restricted hours because of
Canadian stations, and vice versa.
37:
are similar to critical hours, except that the restriction results from the
January 17, 1984, U.S.-Canadian AM Agreement. Canadian restricted hours are called "critical hours" in the U.S.-Canadian Agreement, but in the AM Engineering database, the FCC calls them "Canadian restricted hours" to
41:
Those radio stations that must lower their power during the critical hours are required to do so because this is when the propagation of radio waves changes from
80:
27:
until sunset, local time. During this time, certain
American radio stations may be operating with reduced power as a result of Section 73.187 of the
58:
113:
28:
143:
88:
87:. FCC Mass Media Bureau, Audio Services Division (United States Government). 1997-04-21. Archived from
8:
117:
137:
42:
46:
20:
24:
23:
to two hours after sunrise, and from two hours before
135:
81:"AM Engineering Data Base for Public Release"
75:
73:
59:Pre-sunrise and post-sunset authorization
70:
136:
116:. National Radio Club. Archived from
19:for radio stations is the time from
111:
13:
14:
155:
29:Federal Communications Commission
105:
1:
64:
7:
52:
10:
160:
35:Canadian restricted hours
85:AM Engineering Data Base
114:"Sunrise & Sunset"
144:Broadcast engineering
151:
129:
128:
126:
125:
109:
103:
102:
100:
99:
93:
77:
159:
158:
154:
153:
152:
150:
149:
148:
134:
133:
132:
123:
121:
112:Edmunds, Russ.
110:
106:
97:
95:
91:
79:
78:
71:
67:
55:
12:
11:
5:
157:
147:
146:
131:
130:
104:
68:
66:
63:
62:
61:
54:
51:
17:Critical hours
9:
6:
4:
3:
2:
156:
145:
142:
141:
139:
120:on 2006-11-04
119:
115:
108:
94:on 2007-09-30
90:
86:
82:
76:
74:
69:
60:
57:
56:
50:
48:
44:
39:
36:
32:
30:
26:
22:
18:
122:. Retrieved
118:the original
107:
96:. Retrieved
89:the original
84:
40:
34:
33:
16:
15:
124:2016-02-24
98:2016-02-24
65:References
43:groundwave
31:'s rules.
138:Category
53:See also
47:skywave
21:sunrise
92:(TEXT)
25:sunset
45:to
140::
83:.
72:^
127:.
101:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.