Antenna – device for radiation and reception of radio waves. A. Assignor converts the energy of electromagnetic oscillations of high frequency, lumped in the output of the vibrational transmitter circuits, the energy emitted by radio waves. Conversion is based on the fact that, as you know, alternating electric current is a source of electromagnetic waves. This property is an alternating electric current was first established H. Hertz in the 80’s. 19. on the basis of works by J. Maxwell (for details, see emission and reception of radio waves). A. Admission performs the reverse function – transform energy propagating radio waves in the energy concentrated in the input circuits of the vibrational receiver. Shapes, sizes and designs AG diverse and depend on the length of the radiated or received waves and the appointment of A. They are used as a piece of wire, combinations of these segments, reflecting the metal mirrors of various configurations of the cavities with metallic walls, which cut the slit, the helices of metal wires, etc. Basic characteristics and parameters of A. Most of handing the radiation intensity depends on the direction or, as they say, AA has a direction of radiation. A. This property is graphically represented radiation pattern, showing the dependence on the direction of the electric field radiated wave (measured on the big and the same distance from AA). A. The direction of the radiation leads to increased tension of the wave field in the direction of maximum radiation, and thus creates an effect equivalent to the effects produced by an increase in power output. To quantify the equivalent gain in radiated power introduced the concept of directivity factor (CPV), which shows how many times you want to increase the radiation power by replacing this real hypothetical omnidirectional A. A. (isotropic radiator) to electromagnetic field remained unchanged. Not all delivered to the AG the power output. Some power is lost in the wires and insulators A., and A. Environment Programme (ground supporting A. constructions, etc.). The ratio of radiated power is supplied to the whole efficiency of A. The product is called the gain in efficiency of gain (CG) AG A. Admission is also characterized by shape pattern, gain, efficiency and corporate governance. Its radiation pattern shows the dependence of the emf created by AA at the receiver input, from the direction of arrival of the wave. It is assumed that the field strength at the receiving end does not depend on the direction of arrival of the wave. CPV shows how many times an input AV input circuit in the receiver output at the arrival wave from the direction of maximum reception of more than average (in all directions), the values of power, on condition that the field does not depend on the arrival direction of the wave. CPV receiving A. characterizes its spatial selectivity, which determines the possibility of allocating the received signal in the noise produced by radio signals, ranging from different directions and caused by different sources (see radio interference). Under the efficiency of the receiving A. mean efficiency of the same AA when it is used for transmission. KU reception AA is defined as the product of gain on efficiency. Study of pattern, gain and CG of any AA identical in transmission mode and in receive mode. This property is reciprocal processes of transmission and reception allows us to confine the characteristics of AA only in the mode of transmission.
GSM is Short for Global System for Mobile Communications, one of the leading digital cellular systems. GSM uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency. GSM was first introduced in 1991. As of the end of 1997, GSM service was available in more than 100 countries and has become the de facto standard in Europe and Asia.
Considered the most advanced digital cellular technology, GSM networks are leaders in many typically "digital" services including the Short Message Service (SMS), Over the air (OTA) configuration and GSM positioning. Considering its technology and presence both in Americas and the rest of the world, GSM is in a good position for global roaming and many new GSM phones are called "global phones", since they can be used in virtually any country. The SIM card ("Subscriber Identification Module") is also a unique and essential component of GSM phones. Technically, GSM was built based on the TDMA protocol.