In any communications system, the information to be transmitted must first of all be converted into an electrical quantity which is which is time varying, that is a current or voltage is necessary to represent the signal. In some cases, such as simple telephone link, the waveform of the signal is transmitted directly to the receiving point as a varying current flowing in wires; in other cases, particularly in radio transmission, the signal is used to change or modulate the output of a high frequency generator. The modulation process is defined as the modification of the information according to the signal wave. So the transmission of the information takes place through the modulated wave with high frequency. It is known as the carrier wave, and after modulation it becomes modulated wave. The important types of modulation are amplitude modulation and frequency modulation. In these modulation process, amplitude is varying and frequency is kept constant, it is referred as amplitude modulated wave. Whereas, amplitude kept constant and frequency is varying, it is frequency modulated wave. These modulation process isn’t depend on the circuits which produce the wave forms The communication is defined as the sending and receiving information in the form of electric signals It is started with telegraphy and now it is reached in radio communication. The radio communication is done using the triode tubes. It leads to the invention of transistor, semiconductors devices and integrated circuits More recently, the use of satellites and fiber optics has made communications even more widespread, with an increasing emphasis on computer and other data communications. A modern communications system is first concerned with the sorting, processing and sometimes storing of information before it is transmission. The actual transmission then follows, with further processing and the filtering of noise. Finally we have reception, which may include processing steps such as decoding, storage and interpretation .