Why some AM radio stations have to be turned off for a few hours at night

do you hear any AM station on the radio for the night? You may have wondered why stop broadcasting for a few hours at dawn, or why it tunes worse at night. Everything is due to the laws of physics.

The FM radio stations they only have a range of a few kilometers, but a higher bandwidth, so they are mainly used for stream music, because they offer more quality. Instead, AM or modulated frequency They have more reach 162 kilometersbut their quality is worse, and they are usually used for news programmes, debates, interviewsetc.

These powerful waves from radio stations AM radiothey change their way to spread during the nightDue to the ionosphere.

The ionosphere is a layer of the Earth’s atmosphere located between 80 and 600 km high. It’s formed by ionized gasesdue to solar radiation. These ionized gases are ccharged with electricity.

The ionosphere is the layer that protects us from meteors, since they disintegrate when crossing it. It is also responsible for the formation of the northern lights. But, returning to what concerns us, the ionosphere interferes in the transmission of AM radio waves.

Why do some AM stations turn off at night?

During the day the ionosphere barely reflects radio waves. These travel over the earth’s surface, and have the aforementioned range. around the 160 or 170 kmin the case of AM waves.

But during the eveningWhen the sun goes down, the ionosphere it does not receive as much radiation, and its composition changes. Begins to reflect radio waves, behaving like a mirror. They bounce off it and return to Earth. Successive bounces makes the reach of AM waves is multipliedbeing able to cover hundreds of kilometers.

This, which seems good (the AM radio station could be heard further away), is actually not, because these extended waves interfere with each other, if there are different radio stations broadcasting nearby. The result is that the listener would only receive an annoying sound of static.

To avoid this problem, various solutions are adopted. some stations switch to another channel at night, or redirect the antennas, so that they do not interfere with the competition.

Those who cannot do so should lower the emission power at nightthat’s why they are heard worse, or it costs more to tune in.

But there are old or low-budget stations that cannot do this. So the legislation, at least the americanforces their owners to cut the AM radio signal for a few hours.

So now you know… if at night your favorite AM station is cut offor it is difficult for you to tune in… blame it on the ionosphere.