  # CS601 - Data Communication - Lecture Handout 19

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# Conversions

## Analog To Analog Conversion ### Analog To Analog Conversion Methods ### Amplitude Modulation (AM)

• Amplitude of carrier signal is changed according to the amplitude of modulating signal
• Frequency and phase of the carrier remain the same ### AM Bandwidth

Bandwidth of AM signal (modulated signal) = 2 * bandwidth of modulating signal
Significant spectrum of AM audio = 5 KHz
⇒ 10 KHz bandwidth for an AM station ### AM Band Allocation ### Example 5.18

We have an audio signal with a BW of 4 KHz. What is the BW needed, if we modulate the signal using AM?

### Solution:

• AM signal requires twice the BW of original signal
• BW = 2 * 4 KHz = 8 KHz

### Frequency Modulation (FM)

• Frequency of carrier signal is changed according to the amplitude of modulating signal
• Amplitude and Phase of the carrier signal remain constant ### FM Bandwidth

Bandwidth of FM signal (modulated signal) = 10 * bandwidth of modulating signal
Significant spectrum of FM audio = 15 KHz
⇒ Minimum 150 KHz bandwidth

### FM Band ### FM Band Allocation ### Example 5.19

We have an Audio signal with a BW of 4 MHz. What is the BW needed if we modulate the signal using FM?

## Solution:

• BW = 10 * 4 MHz = 40 MHz
• Phase modulation (PM)
• Simpler hardware requirements
• Phase is modulated with the amplitude
• Amplitude & Frequency of the carrier signal remain constant

## Summary

• Analog-to Analog Conversion
• Frequency Shift Keying (FSK)
• Phase Shift Keying (PSK)