3. COMMUNICATION SYSTEM:The science of communication involving long distance is called Tele communication. Technically speaking the earliest communication system namely line telegraphy invented in eighteenth century. Modern communication consist of following three points:  Spread  Processing  Storage of information

4. A TYPICAL ELECTRONIC COMMUNICATION SYSTEM SOURCE RECEIVER NOISE I|P TRANSD UCER TRANSM -ITTER O\P TRANSD UCER DESTIN- ATION CHANNEL

5. TRANSMITTER :The purpose of a transmitter is to modify the message signal in a form suitable for transmission medium or Simply the channel. This can easily be done through a process known as modulation. MODULATION : It is performed in a transmitter by a circuit called a modulator. A Carrier that has been acted on by an information signal is called a modulated wave. DEMODULATION :is the reverse process of modulation and converts the modulated carrier back to the original information and performed in a receiver.

6. NEED OF MODULATION:  Frequency multiplexing  Practicability of antenna  Narrow banding  Common processing

7. MASTER OSCILLA TIONS RF VOL PWR AMP RF O|P PWR AMP MOD PROCES RF BUFFER AMP MOD PWR AMP MOD FEQ VOL AMP Diagram of high level broadcast transmitter: TRANSMITTING ANTENNA

8. CHANNEL: This is basically a medium,which connects the transmitter to receiver. It may be a coxial wires, Optical fiber and may be a atmosphere. Noise is a major limiting factor in the performance of a Communication system. Noise may be of following categories:  Thermal noise  Intermodulation process  Cross talk  Impulse noise

9. RECEIVER: The main function of this element is to reproduce the original message from the distorted signal. The recovery of the message accomplished by a process known as demodulation which is basically the process,reverse of the modulation. RF AMP AUDIO FREQ AMP LOCAL OSC FREQ MIXER IF AMP DETEC TOR LOUDSPEAKER RECEIVING ANTENNA IF=455KHZ DIAGRAM:

10. MIXING:The mixing process may be defined as a process Of combining two or more signals. In essence there are two ways in which signals can be combined or mixed:  Linear mixing  Non Linear mixing  LINEAR MIXING: It occurs when two or more signals  combine in a linear device, such as passive network or a small signal amplifier. Linear mixing can be explained with the help of two different cases:

11.  SIGNAL INPUT FREQUENCY: Fig(a) shows the amplification of a single input frequency by a linear amplifier. Fig(b) shows the output signal in the time domain. Fig© shows the frequency domain. LINEAR AMP Vin=VaVout=AVa FIG(a)Linear amplification Vout=AVin Vin=Va sinw a t Vout=AVa sinw a t

12. Vin=Va Vout=AVa Fig(B)time domain Fig©frequency domain Va AVa fafb

13.  MULTIPLE INPUT FREQUENCY: Fig(a) shows two input Frequencies combining in a small signal amplifier. Each Input signal is amplified by the gain and mathematically Expressed as : Vout=Avin Vin=Va sin w a t+V b sin w b t Vout=A(Va sin w a t+V b sin w b t) Vout=AVa sinwat+AVb sinwbt Vin=Va Vin=Vb Vout=Ava+AVb FIG(a)Linear amplification fa fb fa

14. Vin=Va Vout=Vb Fig(B)time domain Fig©frequency domain Va AVa fafb AVb Vout=AVa+AVb t t t t t fafb

15. NON LINEAR MIXING:It occurs when two or more Signals are combined in a non linear device such as Diode or large signal amplifier.It is also explained with Different forms:  SIGNAL INPUT FREQUENCY: Fig(a) shows the amplification of a single input frequency by a non linear amplifier. Fig(b) shows the output signal in the time domain. Fig© shows the frequency domain.

16. LINEAR AMP Vin=VaVout=AVa FIG(a)non-Linear amplification fa fb Vin=Va Vout=AVb Fig(B)time domain t t

17. Fig©frequency domain Va AVa fa Vout=Avin+Bvin+CVin Vout=A(Va sin w at)+B(Va sin w at)+C(Va sin w at) 2 2 3 3

18. MULTIPLE-INPUT FREQUENCY:Fig(a) shows two input Frequencies combining in a small signal amplifier. Each Input signal is amplified by the gain and mathematically Expressed as : Vout=A(V1+V2)+B(V1+V2)+- - - - - Vin=A[V1 sinw1t+V2 sinw2t]+b[V1 sinw1t+V2sinW2t]+- - - - - - - - 2 PUTTING THE VALUE OF * I EQUATION I Vo=A[V1 sinw1t+V2 sinw2t]+B[V1 sinw1t+V2sinW2t]+- - - - - - - - 2 3

19. Vin=Va Vin=Vb FIG(a)Linear amplification fa fb fa Vout=A(V1+V2)+B(V1+V2)+- - - - - 2 Vin=Va Vin=Vb Fig(B)time domain Vout=A(Va+Vb)+B(Va+Vb)+- - - t t t 2

20. Fig©frequency domain Va AVa fafb AVb t t fafb