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EXPERIMENT NO.8

TITLE: GENERATION OF FM WAVEFORM FOR GIVEN SIGNAL AMPLITUDE & CARRIER FREQUENCY .

THEORY:

FREQUENCY MODULATION

RECEIVER

TRANSMITTER

Basic system: The basic communication system has :-

TRANSMITTER:- The subsystem that takes information signal and processes it prior to transmission. Transmitter modulates information onto carrier signal, amplifies it and broadcasts like radio. It may also be wining system over the signal.

CHANNEL:- Medium which transports modulated signal to receiver. Air acts as channel for broadcasts like radio. It may also be wining system like cable tv or internet.

RECEIVER:- Subsystem that takes in transmitted signal from the channel and processes it to retrieve the information signal. It must be able to disconnect, discriminate signal from other signals which may be using same channel (called tuning), amplify the signal for processing and demodulates (removes carrier) to retrieve information. It also then processes the information for reception (for example: broadcast on loudspeaker).

MODULATION:

Information signal can rarely be transmitted as is. It must be processed in order to use electromagnetic transmission, it must first be converted from audio into an electric signal. Conversion is accomplished by transducer. After conversion, it is used to modulate carrier signal.

A carrier signal is used for two reasons:

· To reduce wavelength for efficient transmission and reception (optimum antenna size is ½ or ¼ of a wavelength). Typical audio for FM is 100 MHz, with wavelength of 3 m, and could use an antenna only 80 cm long.

· To allow simultaneous use of same channel called multiplexing. Each unique signal can be assigned a different carrier frequency (like radio stations) and still share same channel. Phone company actually invented modulated signal to allow phone conversations to be transmitted over common lines.

The process of modulation means to systematically use modulating signal to vary some parameters of carrier signal. Carrier signal is usually just a simple, single frequency sinusoid (varies in time like sine wave).

MATLAB CODE:

Frequency Modulation

fc=input('Enter the carrier frequency in Hz.,fc=');

fm=input('Enter the modulating frequency in Hz.,fm=');

mi=input('Enter the Modulation index,m=');

t=0:0.0001:1;

c=sin(2*pi*fc*t);

m=sin(2*pi*fm*t);

y=sin((2*pi*fc*t)-(mi*m));

subplot(3,1,1);

plot(t,m,'b');

axis([0 1 -1.5 1.5]);

title('Modulating Signal');

xlabel('Time');

ylabel('Amplitude');

subplot(3,1,2);

plot(t,c,'b');

axis([0 1 -2 2]);

title('Carrier Signal');

xlabel('Time');

ylabel('Amplitude');

subplot(3,1,3);

plot(t,y,'b');

axis([0 1 -2 2]);

title('Modulated Signal');

xlabel('Time');

ylabel('Amplitude');

Observations:-

Enter the carrier frequency in Hz.,fc=40

Enter the modulating frequency in Hz., fm=10

Enter the Modulation index, m=2.5

OUTPUT:-

CONCLUSION:

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