FunWhy are there radio stations that can only be...
Fun

Why are there radio stations that can only be heard at night?

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The radio signal reaches our receiver in two different ways: waves that travel directly to the radio device and waves directed into space that bounce off the ionosphere – a layer of the atmosphere – and return to the earth's surface. The latter have a greater range than the former, because the direct ones are quickly attenuated by the earth's curvature.

However, in medium wave emissions (OM) the sound propagation is limited to the direct wave during the day, because the ionosphere absorbs the energy of the waves at these frequencies. During the night, especially in winter, the lower layer of the ionosphere disappears and the waves can be reflected in higher layers and, therefore, reach further.

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