FM/AM range and temperature
Oct 29, 2008 at 11:41 PM Thread Starter Post #1 of 4

odigg

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Is there a relationship between the range of FM/AM transmission/reception and weather? It seems like the reception of my clock radio is worse now that winter is approaching. Is this actually happening or am I just dreaming?

This may not fit into the DIY section, but people there are people here with technical knowledge about this sort of thing.

Thanks.
 
Oct 30, 2008 at 12:31 AM Post #2 of 4

wolf18t

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I know for sure that Amplitude Modulated signals are influenced by clouds. The AM waves bounce on them and travel farther because of this.

As for Frequency Modulated signals they are more influenced by the topography of your region.
 
Oct 30, 2008 at 9:26 AM Post #3 of 4

error401

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This is a complex field, but the simple answer is that yes, weather conditions do have an effect. Not temperature so much as humidity, cloud cover, precipitation etc. AM also performs much differently during the night, and some stations change their antenna & transmitter configuration for day/night operation to 'protect' other stations in different markets from their signal. Some licenses only allow daytime operation. AM travels much further in the night; just turn on an AM radio well after sunset and you should easily be able to pick up signals from 100s of miles away.

Anyway, yes, it's possible. I suspect though that the more likely culprit is cheap components in your clock radio drifting with temperature.
 
Oct 30, 2008 at 10:17 AM Post #4 of 4

Uncle Erik

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Radio propagation has more to do with the state of the F2 layer of the ionosphere. And yes, that does change with the season and time of day. Also depends on what frequency you listen to - some are more likely to be reflected than others.

AM is much more likely to be affected than FM, since it bounces off the atmosphere more. That's why, under certain conditions, you can pick up AM stations hundreds or thousands of miles away. Even moreso for shortwave and other frequencies. This is why you can pick up shortwave all over the world when it's broadcast from just a single place.

Broadcast FM also bounces, but not nearly as much. It depends a lot more on line-of-sight propagation. Pretty much as long as your antenna can "see" the broadcast tower, you're going to get good reception. Things like steel buildings can mess with this, however. A skyscraper can reflect and scatter the radio, so you'll pick up both the intended broadcast and some scatter reflected back off the building.

If you want to improve reception, get an external antenna and put it on your roof. Radio Shack sells a few decent FM models for $30 or so. You might be surprised at how clear and good analog broadcasts can sound with a good antenna. The antenna is every bit as important as the radio itself.
 

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