Ch5 1 Data communication and networking by neha g. kurale
- 2. 5-2 ANALOG AND DIGITAL Analog-to-analog conversion is the representation of analog information by an analog signal. One may ask why we need to modulate an analog signal; it is already analog. Modulation is needed if the medium is bandpass in nature or if only a bandpass channel is available to us. Amplitude Modulation Frequency Modulation Phase Modulation Topics discussed in this section:
- 3. Figure 5.15 Types of analog-to-analog modulation
- 4. 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.
- 5. Figure 5.16 Amplitude modulation
- 6. The total bandwidth required for AM can be determined from the bandwidth of the audio signal: BAM = 2B. Note
- 7. Figure 5.17 AM band allocation
- 8. 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
- 9. The total bandwidth required for FM can be determined from the bandwidth of the audio signal: BFM = 2(1 + β)B. Where is usually 4. Note
- 10. Figure 5.18 Frequency modulation
- 11. Figure 5.19 FM band allocation
- 12. Phase Modulation (PM) The modulating signal only changes the phase of the carrier signal. The phase change manifests itself as a frequency change but the instantaneous frequency change is proportional to the derivative of the amplitude. The bandwidth is higher than for AM.
- 13. Figure 5.20 Phase modulation
- 14. The total bandwidth required for PM can be determined from the bandwidth and maximum amplitude of the modulating signal: BPM = 2(1 + β)B. Where = 2 most often. Note