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![]() "Matt Beckwith" wrote in message ... The clarity of local AM radio stations is less at night. At night, nearly every AM in the US gets skywave intereference, due to the nature of AM night propagation. Distant signals interfere with what are unobstructed day signals, even if the station has the same power. The only exceptions are clear channel stations, which get a coverage increase due to skywave and being on realtively protected channels. Is there some sort of law that radio stations have to cut their output when it gets dark? Stations, to operate at night (nearly 35% don't) have to protect other stations on the same frequency, sometimes as much as 1000 miles or more away. Because of this, at night they may cut power or directionalize where htey send it to avoid interference, or both. I've noticed that it's the amount of light outside, not the time of day. That is, the lack of clarity occurs whenever it gets dark, not at a certain time each day. The ionesphere makes AM signals skip form just before sunset to just after sunrise. This is why many US stations are daytime only, since they could not run at night without causing interference to others. I always presumed the stations were cutting power to save money, but then why would it be based on light vs dark, rather than on time of day? It's due to the laws of physics. Newer stations protect older ones. And many can not even run at night. |
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