Difference between Sky wave vs LOS wave vs Ground wave

On earth there are two methods of propagation viz. ground wave and sky wave. In the free space, propagation occurs in the straight line or Line of Sight wave. Following section compares Sky wave vs LOS wave vs Ground wave and provides difference between Sky wave, LOS wave and Ground wave.

Ground wave

Ground wave propagation

Ground wave exists between below 2 MHz 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 transmit power is sufficient and hence maximum range of about 5000 miles can be achieved. Optimum antenna size is about λ/2. As the distance from transmitter increases received signal strength decreses and follows exponential curve.

They are also known as surface waves. They are used up to maximum frequency range.
Example: AM radio

Sky wave

Sky wave propagation

Sky wave exists between 2 MHz to 30 MHz and covers ELF, SLF, ULF, VLF, 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, signals can travel number of hops, back and forth. The example of this type is SW radio.

During night 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 the earth surface. It travels with an angle. It travels smaller distances. There are less skip zones with no reception.

LOS wave

Line of sight (LOS) wave propagation

LOS wave exist from above 30 MHz and covers VHF, UHF, SHF, and EHF frequency bands. LOS wave travels in straight line. propagation follows laws of free space. Both transmitting antenna and receiving antenna must be within LOS (Line of Sight). Examples are satellite communication and ground communication.

In the VHF band, LOS signal will be affected by reflection of various objects on the earth.

Refer advantages and disadvantages of Ground wave and Sky wave >> for more information.

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