Compare ground wave and sky wave propogation.
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On earth there are two methods of propagation i.e. ground wave and sky wave.

  • In free space propagation occurs in the straight line or line of sight wave.

  • Below let us compare the difference between ground wave and sky wave propagation.

Ground wave propagation:

  • Ground waves exists between below 2MHz and covers ELF, SLF, ULF, VLF, LF and MF frequency bands.

  • The signal exists in proximity to the earth surface, it follows contour of earth and hence it can propagate considerable distances.

  • At lower frequencies, interference occurs due to atmospheric noise only, here trans it power is sufficient and hence maximum range of about 5000 miles can be achieved.

  • Optimum antenna size is about $\lambda$/2 , As the distance from transmitter increases received signal strength decreases and follows exponential curve.

  • They are also known as surface waves.

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Sky wave propagation:

  • Sky wave exists between 2MHz to 30MHz and covers ELF, SLF, ULF, LF, MF and HF frequency bands.

  • It exists in the sky and depends on reflective characteristics of ionosphere layer, the signal reflected from ionized layer of the atmosphere.

  • In this propagation mode, signal can travel number of hops, back and forth, the example of this type is SW radio.

  • During right time, ionosphere layer is closer to the earth surface, it travels at a flatter angle, it travels larger distances there are more skip zones which results into no reception.

  • During the daytime, ionosphere layer is away from earth surface, it travels with an angle it travels smaller distances.

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