my report in physics

1. 1.3 Elementsof Radio Communication System
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Figure 2.3 shows the elements of a radio communication system. Unlike the telephone transmitter, the microphone used in radio
communication has an electromagnet as main component. The microphone transforms sound waves into electrical signals. These
signals are fed to the modulator. At the same time, an oscillator circuit generates the fixed frequency carrier waves, which are
also fed to the modulator. The modulator puts out the modulated carrier waves.
Figure 2.3 basic elements of a radio communication system
The modulated carrier wave is then sent to the amplifier. The amplifier increases theenergy carried by the wave. The amplified
modulated carrier wave is then sent to thebroadcast antenna. Thechanging current in theantenna generates radio waves that
travel into space.
What is modulatedcarrier wave? Why is modulation necessary? Theelectrical signals bearing the information which
describes sound cannot be transmitted by themselves. They must be carried by theradio waves generated by theoscillator, hence,
the name radio carrier wave. Transfer is done in the modulation process.

2. Modulation is the process by which the carrier wave is changed or varied in relation to theoriginal sound’s loudness and pitch.
Loudness and intensity are related to the amplitude of a wave; pitch is related to frequency. Thus, the two basic ways of
modulating radio waves are amplitude modulation (AM) and frequency modulation (FM).
 Amplitude and Frequency Modulation
A wave’s amplitude is its maximum displacement from equilibrium position. In amplitude modulation, the oscillator emits a
fixed frequency, thecarrier frequency. Theamplitude of the carrier wave is varied according to the intensity (loudness) and
frequency (pitch) of the source wave and thefixed frequency of the source sound wave.
Frequency is thenumber of waves passing a point per unit time. Frequency modulation achieves the same effect as amplitude
modulation. But this time, thecarrier wave has fixed amplitude. Thetransmitted radio waves frequency varies with the sour4ce
sound waves.
Variations in these parameters on thepropagating waves are detected by the receiver, and so thesignal is reconstructed.
Amplitudemodulation is the simpler technique but frequency modulation is less affected by interference and is therefore used
when quality and accuracy of the information are important.
 Bandwidth
The amount of information in a signal determines the maximum frequencies that it contains. This is called thebandwidth of the
signal. Morsecodesent by hand has a comparatively low bandwidth of only a few hertz. To give an acceptable reproduction of
speech, telephonesignal needs bandwidth of about 4000 Hz, while hi-hi music needs about 20000 Hz. Video signals however,
which contain information on the shape, color, and movement in a continuously changing scene often occupy a bandwidth of
more than 5 MHz. In radio transmission, stations are allocated different frequencies so that a receiver can tune into a particular
station and exclude all others. To avoid interference, transmissions frequencies must be spaced apart at least by the bandwidth of
the modulating signal.
We cannot hear radio waves. A receiver intercepts the waves given off by the transmitter and transforms them into audible
sounds.

3.  Receiving Radio Signal
Radio stations broadcast at different frequencies. Theantenna of radio wave receivers, like that of a radio set, picks up all
frequencies. But theradio’s turner circuit selects the frequency received.
The turner circuit of a radio receiver consists of a coil of a wire called an inductor and a variable capacitor. The capacitance of
the capacitor changes when the tuner knob is turned. A certain combination of inductance and capacitance is related to the
frequency of the received signals.
Radio waves from the transmitting antenna of all radio stations reach your radio and set up changing currents in theradio
antenna. When the radio is not properly tuned in, signals from more than one radio stations are received.
A tuner circuits selects thefrequency of the station desired. When the radio is properly tuned in, the frequency of the tuning
circuit resonates and therefore gives preference to the stations frequency. Moving thetuner knob changes theresonant frequency
of the tuner circuit and station heard.
At a certain antenna position, a properly tuned-in radio gives better reception. At this position the antenna is perpendicular to the
direction travel of the transmitted waves. This arises because radio waves are transversewaves.