white space communication

Propagation of EM Waves in Atmosphere - In an Earth environment, electromagnetic waves propagate in ways that depend not only on their own properties but also on those of the environment itself. Since the various methods of propagation depend largely on frequency therefore the complete electromagne..

One desirable feature of radio transmission is that it should be carried without wires (i.e.,) radiated into space. At audio frequencies, radiation is not practicable because the efficiency of radiation is poor. However, efficient radiation of electrical energy is possible at high freque..

Communication Satellites - Communication satellites are normally geostationary satellites. They have devices called transponder which receive signals from an earth station and transmit them in different directions. The signals in the form of electromagnetic radiation are transmi..

AIDS - AIDS is a fatal disease in which the immune system of the body is affected. Acquired Immuno Deficiency Syndrome which is the medical expansion for AIDS was first detected in June 1981 in USA. The disease is caused by a retrovirus - HIV (human immuno deficiency virus). Immune response is prod..

In this, a member of the colony stimulates or informs the other members by showing certain visual acts like i) Worker honeybee informs the other workers of the colony about the direction and distance of food source by its dancing movements (also referred as waggle dance). iii) Sex of an indivi..

Space Launching Vehicles - To place a satellite into orbit it needs to be accelerated in several stages. The required acceleration is produced by firing rockets at various stages of flight. These rockets are fitted into a system called 'launch vehicle' which carries the satellite. By firi..

; complete bending down takes place, as illustrated in the below figur..

Let us now discuss the basic principles of wireless radio communications. We shall mainly concentrate on the principle of amplitude modulation and demodulation. The simplest scheme of wireless communication would be to convert the speech or music to be transmitted to electric si..

If several satellites are spaced around the same orbit in space, the tracks of the satellites will be different due to Earth's rotation about its own axis. But if, for example, four satellites are placed into different orbits with their ascending modes displaced successively by..

The radio horizon for space waves is about four-thirds as far as the optical horizon. This beneficial effect is caused by the varying density of the atmosphere, and because of diffraction around the curvature of the Earth. The radio horizon of an antenna is given, with good approximation,..