DATA COMMUNICATIONS &
NETWORKING
LECTURE-12
Course Instructor : Sehrish Rafiq
Department Of Computer Science
University Of...
LECTURE OVERVIEW
 Types of Link/channel
 Low Pass channel
 Band Pass channel
 Analog to analog modulation
 AM
 FM
 ...
LOW PASS CHANNEL
0 f1
Amplitude
Frequency
BAND PASS CHANNEL
f1 f2
Amplitude
Frequency
TYPES OF LINK/CHANNEL
 A channel or link is either low-pass or band-pass.
 Low-Pass Channel
 A low-pass channel has a w...
ANALOG TO ANALOG
MODULATION
 Modulation of an analog signal or analog-to-
analog conversion is the representation of anal...
ANALOG-TO- ANALOG
MODULATION
TYPES OF ANALOG TO ANALOGTYPES OF ANALOG TO ANALOG
MODULATIONMODULATION
 AM
 FM
 PM
AM(AMPLITUDE MODULATION)
 In AM transmission, the carrier signal is
modulated so that its amplitude varies with the
chang...
AM(AMPLITUDE MODULATION)
AM BANDWIDTH
 The band width of an AM Signal is equal to twice
the bandwidth of the modulating signal and
covers a range ...
AM BANDWIDTH
BAND WIDTH NEEDS OF A RADIO
STATION USING AM
 The bandwidth of an audio signal is usually 5
KHz.
 Each AM radio station ...
BAND WIDTH NEEDS OF A RADIO
STATION USING AM
NOTE
 FCC Federal Communications Commission(FCC)
allows 10KHz for each AM station.
Example 1Example 1
We have an audio signal with a bandwidth of 4 KHz.
What is the bandwidth needed if we modulate the sign...
FREQUENCY MODULATION (FM)
 In FM transmission, the frequency of the carrier
signal is modulated to follow the changing
vo...
FREQUENCY MODULATION
BANDWIDTH REQUIREMENTS
FOR FM
 The bandwidth of an FM signal is equal to 10
times the bandwidth of the modulating signal....
FM BANDWIDTH
BAND WIDTH NEEDS OF A RADIO
STATION USING FM
 The bandwidth of an audio signal(speech and
music ) broadcast in stereo is ...
FM BANDWIDTH ALLOCATION
PHASE MODULATION
 In PM transmission, the phase of the carrier
signal is modulated to follow the changing
voltage level(a...
PM SIGNAL
ENOUGH FOR TODAY!!!
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Lecture 12

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Lecture 12

  1. 1. DATA COMMUNICATIONS & NETWORKING LECTURE-12 Course Instructor : Sehrish Rafiq Department Of Computer Science University Of Peshawar
  2. 2. LECTURE OVERVIEW  Types of Link/channel  Low Pass channel  Band Pass channel  Analog to analog modulation  AM  FM  PM
  3. 3. LOW PASS CHANNEL 0 f1 Amplitude Frequency
  4. 4. BAND PASS CHANNEL f1 f2 Amplitude Frequency
  5. 5. TYPES OF LINK/CHANNEL  A channel or link is either low-pass or band-pass.  Low-Pass Channel  A low-pass channel has a width with frequencies between 0 and f.  Band-Pass Channel  A band-pass channel has a bandwidth with frequencies between f1 and f2.
  6. 6. ANALOG TO ANALOG MODULATION  Modulation of an analog signal or analog-to- analog conversion is the representation of analog information by an analog signal.  Modulation is needed if the medium has a band nature or if only band-pass bandwidth is available to us.  E.g. radio station
  7. 7. ANALOG-TO- ANALOG MODULATION
  8. 8. TYPES OF ANALOG TO ANALOGTYPES OF ANALOG TO ANALOG MODULATIONMODULATION  AM  FM  PM
  9. 9. AM(AMPLITUDE MODULATION)  In AM transmission, the carrier signal is modulated so that its amplitude varies with the changing amplitudes of the modulating signal.  The frequency and phase of the carrier remains the same.  Only the amplitude changes to follow variations in the information.  The modulating signal becomes an envelope to the carrier.
  10. 10. AM(AMPLITUDE MODULATION)
  11. 11. AM BANDWIDTH  The band width of an AM Signal is equal to twice the bandwidth of the modulating signal and covers a range centered on the carrier frequency.  BWt = 2 x BWm.
  12. 12. AM BANDWIDTH
  13. 13. BAND WIDTH NEEDS OF A RADIO STATION USING AM  The bandwidth of an audio signal is usually 5 KHz.  Each AM radio station needs a minimum bandwidth of 10KHz.  AM stations are allowed carrier frequencies anywhere between 530 and 1700 KHz(1.7 MHz).  Each station’s carrier frequency must be separated by at least 10 KHz(one AM bandwidth) to avoid interference.
  14. 14. BAND WIDTH NEEDS OF A RADIO STATION USING AM
  15. 15. NOTE  FCC Federal Communications Commission(FCC) allows 10KHz for each AM station.
  16. 16. Example 1Example 1 We have an audio signal with a bandwidth of 4 KHz. What is the bandwidth needed if we modulate the signal using AM? Ignore FCC regulations. SolutionSolution An AM signal requires twice the bandwidth of the original signal: BW = 2 x 4 KHz = 8 KHz
  17. 17. FREQUENCY MODULATION (FM)  In FM transmission, the frequency of the carrier signal is modulated to follow the changing voltage level(amplitude) of the modulating signal.  The peak amplitude and the phase of the carrier signal remains constant.  As the amplitude of the information signal changes, the frequency of the carrier changes correspondingly.
  18. 18. FREQUENCY MODULATION
  19. 19. BANDWIDTH REQUIREMENTS FOR FM  The bandwidth of an FM signal is equal to 10 times the bandwidth of the modulating signal.  Like AM bandwidth, FM also covers a range centered on the carrier frequency.
  20. 20. FM BANDWIDTH
  21. 21. BAND WIDTH NEEDS OF A RADIO STATION USING FM  The bandwidth of an audio signal(speech and music ) broadcast in stereo is almost 15 KHz.  Each FM radio station therefore needs a minimum bandwidth of 150 KHz.  The FCC allows 200 KHz(0.2 MHz) for each station to provide some room for guard bands.  FM stations are allowed carrier frequencies anywhere between 88 and 108 MHz.  FCC requires that in a given area only alternate bandwidth allocations may be used.
  22. 22. FM BANDWIDTH ALLOCATION
  23. 23. PHASE MODULATION  In PM transmission, the phase of the carrier signal is modulated to follow the changing voltage level(amplitude) of the modulating signal.  The peak amplitude and frequency of the carrier signal remain constant.  As the amplitude of the information signal changes, the phase of the carrier changes correspondingly.
  24. 24. PM SIGNAL
  25. 25. ENOUGH FOR TODAY!!!

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