Critical Hours is that time from sunrise to two hours after sunrise, and from two hours before sunset until sunset, local time. During that time, certain American radio stations may be operating with reduced power as a result of Section 73.187 of the Federal Communications Commission's Rules.
Canadian Restricted Hours 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 data base, the FCC calls them "Canadian Restricted Hours" to 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.
Those radio stations that are required to lower their power during the Critical Hours are required to do so because this is when the propagation of radio waves changes from groundwave to skywave (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 with nearby frequencies.
Famous quotes containing the words critical and/or hours:
“Most critical writing is drivel and half of it is dishonest.... It is a short cut to oblivion, anyway. Thinking in terms of ideas destroys the power to think in terms of emotions and sensations.”
—Raymond Chandler (1888–1959)
“The clock runs down
timeless and still.
The days and nights turn hours to years
and water in a gutter marks the circle of another world
hating, resentful, and afraid
stagnant, and green, and full of slimy things.”
—Margaret Abigail Walker (b. 1915)