know sky and space wave propagation difference , definition , formula , example , compare ?
The transmission of information through space as communication channel is space communication. it means in Space Communication the communication channel is space works. means the information passes through space or we can say the medium in this communication process is works as space.
example – Radio, television and satellite transmissions use space communication. The various modes of space propagation are
(i) ground or surface wave propagation,
(ii) sky wave propagation,
(iii) space wave propagation, and
(iv) satellite communication
Ground or Surface Wave Propagation
The radiowaves which travel along the surface of the earth from the transmitter to the receiver are called ground or surface waves. The transmission of information through radiowaves is called ground or surface wave propagation (or communication). In ground wave transmission, the intensity of the radio signal falls as it travels due to absorption by the ground and also by the gases in the atmosphere. As a result, the signals become weak and after travelling some distance, they die out. Due to this, the ground wave transmission is not suitable for long distance communication.
Sky Wave Propagation
Radiowaves, which are directed towards the sky from a transmitter at a certain location on the earth and are reflected back from the ionosphere towards another location on the earth are called sky waves. The transmission of information through sky waves is called sky wave propagation (or communication). Sky wave transmission is suitable for frequencies in the range 2 MHz to about 20 MHz. Above 30 MHz, the ionosphere does not reflect the waves; they are transmitted through it.
Space Wave Propagation
Radiowaves which travel in the earth’s troposphere (layer of atmosphere closest to earth) from a transmitting antenna (at a transmitting station) to a receiving antenna (at a receiving station) are called space waves. They have frequencies higher than 30 MHz. The transmission of information through space waves is called space wave propagation (or communication). The maximum distance up to which signal from an antenna of height at a TV transmitting station can reach directly is given by
dmax = √2Rht + √2Rhr
where ht = height of transmitting tower, hr = height of receiving tower and R = radius of the earth. This mode of transmission in called Line of Sight (LOS) mode.
question – A transmitting antenna is at the top of a tower of height 64 m and the receiving antenna is at the top of a tower of height 32 m. Calculate the maximum distance between them for satisfactory transmission in LOS mode. Given, radius of earth = 6400 km
answer : dmax = 48.8 km
Satellite Communication The mode of communication in which microwave signals propagate from a transmitter at a certain location on earth to a receiver at another location via a satellite is called satellite communication. The satellite used is a geostationary satellite. For global communication (i.e. to transmit signals to all locations on earth), three geostationary satellites parked 120° apart from each other are used.