TV signal are electromagnetic wave which can be propagated through space ,it depends upon the wavelength of signal there are three method for propagation of wave take place:-
- Ground wave propogation
- Sky wave propogation
- Space wave propogation
1.Ground wave propogation:-In ground wave propagation waves are vertically polarized. The electromagnetic wave which radiates at 0 or a small angle with ground are guided by conducting surface of the ground along which they are propagated such this type of wave are called ground wave or surface wave propagation.It use below the 2 MHz.
2.Sky wave propogation:-
In this wave propogation the electromagnetic wave signal are transmitted in sky and then signal are reflected by inosphere by total internal reflection and get to the receiving antenna.
There are different types of layer are introduced in this propogation system which is given below:-
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere and ionosphere
- Exosphere
- Magnetosphere
Inosphere exist or contain three type of layer D, E, F layer.
D layer :- 60 km to 80 km
E layer:- 100 km to 120 km
F layer:- 250 km to 350 km
During night layer D Vanished. Due to ionization the radio waves are reflected as the increasing ionization provides decreasing refractive index. So wave travel from denser medium to rarer medium and hence bends away from the normal . In this process total internal reflection takes place and electromagnetic waves are reflected back towards.
It use 3 MHz to 30 MHz for propogation of wave.
3.Space wave propogation:-
In this mode the propagation of electromagnetic wave the energy travel in the space direct from the transmitting antenna to receiving antenna . It neither using any conducting surface not the ionosphere. In this mode the loss of energy is only due to spreading of the energy and antenna characteristic. Therefore this is the only mode available for the TV wave which uses VHF and higher band.
It use 30 MHz to 300 MHz for propogation of wave.
0 Comments