different types of wave propagation

(a) Ground wave propagation:

The type of propagation in which radio waves propagate from transmitting antenna to receiving antenna following the surface of the earth is called ground wave propagation.

Electromagnetic waves which are vertically polarised can travel by this mode.

The intensity at the signal falls with the distance as radiowaves induce current in the ground over which they pass. As the wave propagate, the corresponding angle of tilt goes on increasing after a certain time the wave dies out.

Frequency at which ground waves travel is upto 1500 KHZ.

c = f.λ

wavelength, λ = 200m

Used for local broadcasting, ship communication etc.

b) Sky wave propagation:

The propagation of Radiowaves from tranmitting antenna to receiving antenna via reflection from the ionosphere is called sky wave propagation.

The ionosphere region consists of ions which extends from a height of 60km to 300 km.

As we go higher in the ionosphere, there is an increase in the free electron density consequently there is decrease in the Refractive Index (μ).

Thus, as radiowave travel up in the ionosphere it travels from denser medium to rarer medium. It continuously bends from its path till it suffers total internal reflection to reach back to the Earth.

c) Space wave propogation:

Space wave propagation can be achieved in the following 2 ways:

1) LOS Communication

2) Satellite Communication

Consider a TV antenna OP of height h. The transmitted signal cannot be received beyond points R1 and R2.

OR1$O{R}_1$ and OR2$O{R}_2$ are maximum distance from the antenna.

let OR1=OR2=d$O{R}_1=O{R}_2=d$

from ΔPCR1$∆PC{R}_1$

CP2=PR21+(CR1)2(R+h)2=PR2+R2InΔPOR,PR21=h2+dr2(R+h)2=h2+dr2+R2R2+2hR+h2=h2+dr2+R2dr=2Rhr−−−−√(for transmission)Similarly,dR=2RhR−−−−−√d=dr+dR