To understand how that can happen you need to know that the main way that AM radio signals travel is by ground wave, literally hugging the earth.
32.
The last interference minimum on the ground ( z = 0 ) between the ground wave and the first sky wave is at a horizontal distance of
33.
A : The so-called action program, or planning for digital ground wave broadcasting, could be completed in four to five years, ahead of the scheduled completion in 2010.
34.
HF communications are in the 2-30 MHz band, which provides Beyond Line-Of-Sight ( BLOS ) communication ( HF Sky Wave or HF Ground Wave ) optimized for transmission up to.
35.
The result was a signal that offered a daytime ground wave range of 2, 250 miles, nighttime ground wave of 1, 650 miles and skywaves out to 3, 000 miles.
36.
The result was a signal that offered a daytime ground wave range of 2, 250 miles, nighttime ground wave of 1, 650 miles and skywaves out to 3, 000 miles.
37.
The frequency modulation method exploits the fact that there is a path difference between the ground wave and the reflected wave, meaning they travel different distances from sender to receiver.
38.
In contrast to line-of-sight propagation, at low frequency ( below approximately 3 MHz ) due to diffraction radio waves can travel as ground waves, which follow the contour of the Earth.
39.
At distances that are typically towards the edge of the ground wave coverage area, some sky-wave signal may also be present, especially at night when the D layer attenuation is reduced.
40.
Most broadcast antennas use either ground wave propagation ( a slight refraction towards the ground ) to reach their nearby listeners, and thus want a low angle in the vertical plane.
