Why ground wave is use in Amplitude modulation station>?

Question

Why ground wave is use in Amplitude modulation station>

Answer 1

Hi. The AM signals are used in two basic ways. Commercial broadcasts (the "AM" band) and in ham radio. AM CAN bounce off the F1 and F2 layers of the ionosphere, but usually only after sunset. (That's why most AM stations have to cut back their power due to FCC regulations after dark.)

Answer 2

It is nothing to do with the modulation scheme used, it is the frequency.

The atmosphere has a refractive index and the earth has another. Electromagnetic waves will travel along this interface as surface waves (often called ground waves). The earth is conductive, but with a fairly high resistance. This causes a loss which increase with frequency. The MF band suffers relatively low losses and so is suitable fro ground wave transmission. The LF band suffers even lower losses and so is good for long distance communication. As a matter of interest, VLF not only suffers low losses of the surface wave but will also penetrate water to a reasonable depth and can be used to communicate with submarines (provided they are not too deep).

As the frequency is increased, from MF to HF, the ground wave suffers considerable attenuation but the sky wave is effectively refracted by the ionosphere making long distance communication possible at HF.