What is Radio Communication System ?

Radio communication system means the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic field that pass though the air and vacuum of space . Information is carried by systematically changing (modulating) some property of the radiated such as amplitude, frequency.

Fig.01.

Radio communication furnishes a very useful and interesting application of electronics. There are two types of radio communication, namely,

1. Radio telegraphy.

2. Radio telephony.

1. Radio telegraphy :-

In radio telegraphy , a message is transmitted by means of a telegraphic code that periodically interrupts continuous radio waves.

2. Radio telephony:-

In radio telephony , speech or music is broadcast with the help of radio waves modulated by the speech or the music.

Radio communication was known as wireless since wires are not necessary in the transmission of information , which is done by means of radio waves.

The elements of a radio communication system :-

a telegraphic key or a microphone that controls the radio waves in accordance with the information or the intelligence to be transmitted.
a transmitter to produce radio waves.

a transmitting antenna that radiates the radio waves in some specified direction or in all directions.
a receiving antenna that receive a part of the radiated wave.
a receiver that selects, amplifiers, and detects the desired signal.
a headphone or loudspeaker that converts the detected electrical signal into sound, thus reproducing the information.

RADIO TRANSMITTER :-

In a radio transmitter, a fixed-frequency radio wave , referred to as the carrier wave is generated. The electrical form of the intelligence (e.g., speech or music) to be broadcast is superimposed on the carrier.

In radio telephony , this is accomplished by modulating the amplitude or the frequency of the carrier wave by means of the intelligence.

The resulting wave is carried to the transmitting antenna for radiation.

Fig.02

Amplitude-Modulated Transmitter :-

the basic blocks of an amplitude modulator (AM) radio transmitter. We briefly discuss this block as follows :

RF master oscillator : A crystal -controlled master oscillator is used to operate the transmitter at a desirable fixed radio frequency (RF). The power output of the master oscillator, being not sufficiently large, is amplified in several stages to the desired level.
RF buffer amplifier : This amplifier isolates the master oscillator from the succeeding stages, so that the variations of coupling and antenna loading do not influence the oscillator frequency.
Frequency multipliers : Crystals can't generate very high carrier frequencies. To obtain such frequencies, the frequency multipliers used to multiply the frequency of the master oscillator output signal to the required value.
Audio amplifier : This amplifier is used to amplify the audio signal output of the microphone that converts the speech or the music to be transmitted into equivalent electrical signals.
Modulator : The function of the modulator is to amplitude modulate the RF carrier in accordance with the amplified audio signal.
Intermediate RF amplifier : The output of the modulator is conveyed to this stage for amplification for low-level modulation.
RF Power amplifier : The modulated carrier is fed to this stage for final amplification before being carried to the antenna. For high-level modulation, the modulator output is fed to the final RF amplifier, as indicated by the arrow and it's soon Fig.no.3.
Power supply : A common power supply is used to supply the requisite power to all stages of the transmitter.

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