Why does my radio reception improve at night?

[James Boston]

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So you can imagine how ridiculous it was when they were at 500k watts.

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It is rumored that XERF used to power up to 1,000,000 watts on occasion in the 1920's. The KGB listened to it to learn English.

[whiskeytown]

SW radio waves ALSO travel better at night on certain frequencies (and days as I recall) -

here's the thing...two stations both broadcasting at 650AM will create what's described as nasty distortion/static in between them...so that's why so many power down.

In the 1920's, this wasn't an issue, as so few radio stations existed and AM radio waves could bounce a hell of a ways - but as you got more stations, you had to change that.

FM, on the other hand, works totally by line of sight from the tower, technically - (AM uses the whole tower for transmitting, FM uses a transmitter at the TOP of the tower)- so FM radio waves don't bounce and travel a lot less further.

some good trivia for you..

just a guy who owns a SW radio and used to listen before he could pick up the BBC world service online....

oh yah....also a broadcasting major [img]/images/graemlins/wink.gif[/img]
RB

[jar]

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SW radio waves ALSO travel better at night on certain frequencies (and days as I recall) -


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Yeah, the Maximum Usable Frequency, or MUF, for a given propagation path varies based on time of day, season, weather, and solar conditions. The highest frequency available that is still lower than the MUF will give the most efficient propagation.

The MUF is higher during the day than it is at night. Speaking from an Amateur radio perspective, the 40 and 80 meter (7 and 3.5MHz) bands are generally used at night, because the propagation is bad during the day, and solar noise is much stronger than skywave signals. The mid HF bands, 30 and 20 meters (10 and 14MHz) are usually open to somewhere round the clock. The upper bands, 10 and 15 meters (21 and 28MHz) are generally only useful during the day.

Also, the MUF tends to be higher during years of high sunspot activity. We're currently near the bottom of the sunspot cycle. The 10 meter (28MHz) amateur band, which will work round the world with 5 watts to a wet noodle at cycle peaks is near useless for long distances other than brief periods during the day, and at the gray lines.

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FM, on the other hand, works totally by line of sight from the tower, technically - (AM uses the whole tower for transmitting, FM uses a transmitter at the TOP of the tower)- so FM radio waves don't bounce and travel a lot less further.


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Just to keep this clear, the AM/FM distinction is not the reason for this, it's the frequency ranges of the AM and FM broadcast spectrum. The reason for AM using the whole tower is that the wavelengths in the AM BCB are monstrous. 1MHz has a wavelength of 299.79 meters. 100MHz has a wavelength of 2.9979 meters. The antenna on your car is a 1/4 wave "ground plane" antenna for this frequency range (88-108MHz). AM reception uses some trickery, because you clearly couldn't have a 200 foot high antenna on the car.