data communication chapter 05 (2), Slides of Data Communication Systems and Computer Networks

Download data communication chapter 05 (2) and more Slides Data Communication Systems and Computer Networks in PDF only on Docsity!

Chapter 5

Analog Transmission

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5-2 5-2 ANALOGANALOG ANDAND DIGITALDIGITAL

Analog-to-analog conversion is the representation of Analog-to-analog conversion is the representation of analog information by an analog signal. One may ask analog information by an analog signal. One may ask why we need to modulate an analog signal; it is why we need to modulate an analog signal; it is already analog. Modulation is needed if the medium is already analog. Modulation is needed if the medium is bandpass in nature or if only a bandpass channel is bandpass in nature or if only a bandpass channel is available to us. available to us.  (^) Amplitude Modulation  (^) Frequency Modulation  (^) Phase Modulation Topics discussed in this section: Topics discussed in this section:

Amplitude Modulation

 A carrier signal is modulated only in amplitude value  The modulating signal is the envelope of the carrier  The required bandwidth is 2B, where B is the bandwidth of the modulating signal  Since on both sides of the carrier freq. fc, the spectrum is identical, we can discard one half, thus requiring a smaller bandwidth for transmission.

Figure 5.16 Amplitude modulation

Figure 5.17 AM band allocation

Frequency Modulation



The modulating signal changes

the freq. fc of the carrier

signal



The bandwidth for FM is high



It is approx. 10x the signal

frequency

Figure 5.18 Frequency modulation

Figure 5.19 FM band allocation

Figure 5.20 Phase modulation

The total bandwidth required for PM can

be determined from the bandwidth

and maximum amplitude of the

modulating signal:

B

PM

= 2(1 + β)B. )B.

Where  = 2 most often.

Note