ANALOG AND DIGITAL COMMUNICATION SYSTEMS

  MULTIPLEXING TECHNIQUES :- Define multiplexing ? need for multiplexing ? Types of multiplexing techniques ? Block diagram of FDM ? Block diagram of TDM ? Applications of TDM,FDM? Advantages & Disadvantages  of TDM ? Advantages & Disadvantages  of FDM ? Compare FDM,TDM ? NEED for MODEM ? Define modem ?different types of modem ? Draw block diagram of DSL ? Draw block diagram of ADSL ? Draw band diagram for ADSL ?

  TRANSMITTERS AND RECEIVERS Specifications of AM transmitters ? Specifications of FM transmitters ? Differences between AM low level & AM high level transmitters ? Block diagram of AM low level transmitter ? Block diagram of AM high level transmitter ? Block diagram of Arm strong FM transmitter *(indirect method) ? Define sensitivity, selectivity, fidelity ? Block diagram of TRF receiver? Define Heterodyning , Super Heterodyning ? Block diagram of Super heterodyne AM receiver? Need of AVC/AGC ? Draw circuit diagram of demodulation in AM receiver ? Draw circuit diagram of Foster Seely Discriminator ?

 UNIT 3 PREPARATION SHORTS :- Give different types of encoding  formats in digital encoding ? Different types of data transmission techniques ? Advantages and disadvantages of parallel data transmission ? Advantages and disadvantages of serial data transmission ? Short notes on asynchronous transmission? Short notes on synchronous transmission? Need for start and stop bits in asynchronous transmission ? Advantages and disadvantages asynchronous transmission ? Advantages and disadvantages synchronous transmission ? Define bit overhead ,overhead efficiency ? What are error control techniques ? Different types of error detection and control / correction methods? Need for digital modulation ? Define bit rate and baud rate ? Basic types of digital modulation techniques ? Draw the wave forms for ASK , PSK, FSK ? Compare ASK , FSK, PSK? Block diagram of  ask , fsk , psk ?

  DIGITAL COMMUNICATION PRINCIPLES:- Define communication ?classification of communication? Define analog and digital signals Advantages and disadvantages of digital communication over analog communication ? Information capacity of a channel ? Convertion of analog signal to digital signal? Define sampling ? explain sampling theorem? Define nyquist and aliasing effect ? Draw the waveform for PAM,PWM,PPM? Compare PAM , PWM ,PPM? Define sampling ,quantization,encoding ? Draw the block diagram for PCM coding and decoding ? Applications ,advantages,disadvantages of PCM ?

  ANALOG MODULATION TECHNIQUES:- Basic elements of communication system? Applications of different frequencies in spectrum? Define modulation ? need for modulation ? Classification of various modulation techniques? Difference between base band,carrier,modulated signal ? Define AM,FM,PM? Define modulation index ?draw the wave forms for M<1,M=1,M>1 ? Dffects of over modulation? Advantages & dis advantages of FM over AM? Advantages and dis advantages of DSB-SC, SSB-SC? Define pre-emphasis & de-emphasis with circuits diagrams ? Advantages of pre-emphasis and de-emphasis ? Define noise ? effects of noise in communication systems ? Classification of noise ? Define signal to noise ration ,noise figure ,noise temperature ?

  BASIC ELEMENTS OF COMMUNICATION SYSTEM      INFORMATION SOURCE :   It produces message signal which we want to send.   It converts message signal to electrical signal .(it is also called as input transducer)     TRANSMITTER :   It converts the message signal to suitable form of propagating signal over communication channel.   The process of conversion is possible by modulation. And finally sends the signal through the channel.     CHANNEL :   The path for transmitting a signal is called channel.    It is a medium between transmitter and receiver ( wire / wireless ),use for signal transmission.                      NOISE :      The unwanted form of signal energy is known as noise.        It enters the communication system through channel.          RECEIVER :     The main fun...

  Applications of different frequency spectrum?  ELF     EXTREME LOW FREQUENCY VF        VOICE FREQUENCY VLF      VERY LOW FREQUENCY LF         LOW FREQUENCY MF        MEDIUM FREQUENCY HF         HIGH FREQUENCY VHF      VERY HIGH FREQUENCY UHF      ULTRA HIGH FREQUENCY SHF       SUPER HIGH FREQUENCY EHF      EXTREME HIGH FREQUENCY

MODULATION :      THE PROCESS OF CHANGING SOME CHARACTERISTICS OF CARRIER SIGNAL (AMPLITUDE  / FREQUENCY / PHASE)   IN ACCORDANCE WITH THE INSTANTANEOUS AMPLITUDE OF THE MESSAGE SIGNAL IS KNOWN AS MODULATION . NEED FOR MODULATION : I) REDUCE THE HEIGHT OF ANTENNA II) FOR MULTIPLEXING III) FOR EASY RADIATION IV) AVOID MIXING OF SIGNALS V) REDUCTION OF NOISE .

CLASSIFICATION OF  VARIOUS MODULATION   TECHNIQUES : MODULATION TECHNIQUES

 BASE BAND SIGNAL : The message signal which is coming form an information source is called base band signal it is a low frequency signal it is the output of information source it combines with the carrier to generate modulated signal CARRIER SIGNAL : The signal which is used to carry message signal is called carrier signal it is a high frequency signal it is the output of oscillator it combines with the message to generate modulated signal MODULATED SIGNAL : The output of modulator is called modulated signal it is a high frequency signal it contains both message information and carrier properties it is the output of modulator

  MODULATION :      THE PROCESS OF CHANGING SOME CHARACTERISTICS OF CARRIER SIGNAL  (AMPLITUDE  / FREQUENCY / PHASE)   IN ACCORDANCE WITH THE INSTANTANEOUS AMPLITUDE OF THE MESSAGE SIGNAL IS KNOWN AS  MODULATION . AMPLITUDE MODULATION :- THE PROCESS OF CHANGING AMPLITUDE OF CARRIER SIGNAL  IN ACCORDANCE WITH THE INSTANTANEOUS AMPLITUDE OF THE MESSAGE SIGNAL IS KNOWN AS AMPLITUDE   MODULATION . FREQUENCY MODULATION :- THE PROCESS OF CHANGING FREQUENCY OF CARRIER SIGNAL  IN ACCORDANCE WITH THE INSTANTANEOUS AMPLITUDE OF THE MESSAGE SIGNAL IS KNOWN AS  FREQUENCY   MODULATION . PHASE MODULATION :- THE PROCESS OF CHANGING PHASE OF CARRIER SIGNAL  IN ACCORDANCE WITH THE INSTANTANEOUS AMPLITUDE OF THE MESSAGE SIGNAL IS KNOWN AS  PHASE   MODULATION .

   Modulation index :- It is defined as the ration of maximum amplitude of message signal to  maximum amplitude of carrier signal .                    M= Vm / Vc           M = modulation index           Vm = maximum amplitude of message signal         Vc = maximum amplitude of carrier signal

  Modulation index :- It is defined as the ration of maximum amplitude of message signal to maximum amplitude of carrier signal .                    M= Vm / Vc           M = modulation index           Vm = maximum amplitude of message signal         Vc = maximum amplitude of carrier signal Effects of over modulation? if M>1 it is called as over modulation ,due to this some problems will occurs in transmission . transmission quality will be poor envelop will occur in receiver(negative peak clipped off) excessive bandwidth required instability in carrier voltage,frequency interference with neighboring station signal may occur

 Merits of FM over AM :- high s/n ratio in FM compared to AM . less power required for radiation . by using amplitude limiters we can reduce noise in FM. FM broadcasting used for upper UHF and VHF ranges. In FM if two signals with same frequency received ,it captures strong signal ,and eliminate weak signal In case of FM signal, the adjacent channels are separated by guard bands to reduce interference .  There is no change in FM amplitude , amplitude variation causes more noise . dis advantages :- FM systems are costlier than AM systems . FM involves with complicated circuitry . FM systems have a much wider bandwidth than AM systems . The antennas for FM systems should be kept close for better communication.

ADVANTAGES AND DISADVANTAGES OF DSB-SC : ADVANTAGES OF DSB-SC: It saves more power than AM less bandwidth required compare to AM low power consumption DSB-SC generation is simple compare to AM DISADVANTAGES OF DSB-SC : bandwidth required is same as AM Product detector required for demodulation detection of DSB-SC signal is complex  ADVANTAGES AND DISADVANTAGES OF SSB-SC : ADVANTAGES OF SSB-SC: Less noise in SSB-SC It saves more power than AM & DSB-SC less bandwidth required compare to AM & DSB-SC DISADVANTAGES OF SSB-SC : Complex process of generation and reception IN SSB-SC SSB-SC not used for transmission of good quality of signals