Conversions
Analog To Analog Conversion
- Representation of Analog information by an Analog signal
- For Example: Radio
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 signalSignificant 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 signalSignificant 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)
- Quadrature Amplitude Modulation (QAM)
Reading Sections
- Section 5.4, “Data Communications and Networking” 4th Edition by Behrouz A. Forouzan