Telephone communication

Telephony is important kind of communication. It is transmission of speech over distance by means of electricity. Telephone set includes a transmitter, electric network and receiver. The transmitter or microphone consists of a diaphragm, carbon chamber with carbon granules, insulating spacer and conductor. The electric current passes through the diaphragm and carbon granules. When we speak we produce sound waves which make the diaphragm vibrate. The diaphragm in its turn pushes the carbon granules which makes more or fewer contacts and decreases or increases the resistance. Thus the waves of electric current vary depending on the sounds we produce and pass along the line and finally reach the receiver.

The receiver consists of electromagnetic coils, a steel ma magnet and a diaphragm. A variable current passing through the magnet’s coil makes the diaphragm vibrate. The frequency of these oscillations is the same as that of the transmitter. Therefore, the receiver reproduces the same sounds as are spoken onto the microphone.

The telephone was designed in 1875 by Alexander Bell. Later on the development of the telephone changed the construction, it became more complex. Some elements were used in the circuit to provide better transmission of speech. Further on the development improved the switching system. Now very complex telephone constructions are used and a new kind of telephones appeared.

Radio communication

Radio communication is the transfer of high frequency energy from the transmitter to the receiver without wires.

Radio is a device that transmits and receives signals and programs by means of electromagnetic waves. Since the process of radio communication includes transmission and reception of signals, the necessary components of radio are a transmitter and a receiver.

The transmitter is a device that produces radio-frequency energy. The main parts of a transmitter are high-frequency oscillator including oscillatory circuit and one or two amplifiers.

When we speak into the microphone the resistance varies with the audio frequency. An alternating current is established in the microphone and antenna circuits and the frequency is the same as the audio frequency.

Electric oscillations produced in the antenna of the transmitter may travel in different directions.

In the receiver the high-frequency current is rectified by means of a detector or rectifier and passes through the telephone. It is demodulated and the sounds, produced at the transmitting station are reproduced.

Radio waves are the waves of very high frequency; they travel through space at the speed of light. They differ from other waveforms only in frequency range (a number of vibrations per second).

Mobile Cellular

A mobile phone can make and receive telephone calls to and from the public telephone network which includes other mobiles and fixed-line phones across the world. It does this by connecting to a cellular network owned by a mobile network operator.

Since 1980s mobile telephony has undergone an enormous expansion. The networks have become more powerful and the market has grown. There are lots of different services, such as voice banks and data transmission.

The two main types of technologies in use are analogue and digital. The first systems were analogue ones. Digital systems are more recent, but they are becoming common all over the world. They have several advantages, such as capacity, reliability and security. All mobile phone conversations are safe from eavesdropping. They also offer extra services, especially for business customers. In addition, digital systems have greater flexibility and you can make telephone calls within the countries as roaming is worldwide.

GSM – that is Global system for mobile communication. That is European digital standard which is rapidly spreading in Europe and other parts of the world. The main threat to GSM comes from CDMA, a come division multiple access technology which uses frequencies more economically than tome division system used by GSM. The advantages of CDMA may give it a competitive edge over GSM, especially in markets like the USA where the airways are already crowded. If one system is widely adopted, the regular traveler can have just one mobile phone which he or she uses whilst on the move in a number of countries.