Amplitude Modulation Variants: DSB, SSB, and VSB

Lecture Overview

Three types of amplitude modulation: DSB, SSB, and VSB
Recap: Demodulation of AM and introduction of amplitude demodulation (envelope detector)
Objective: Discuss the properties, advantages, and disadvantages of DSB, SSB, and VSB variants

Class test on March 17th will cover the first six lectures
Upcoming schedule updates:
- Complete weekly progress check by Sunday
- Bank holiday on May 3rd; sessions moved (Monday's session to Wednesday and vice versa)
Updated schedule on Canvas

Envelope Detector: Diode rectifier, resistor-capacitor low-pass filter
- Performance: Slight distortion acceptable if time constant RC is chosen appropriately
- Type: Non-coherent/asynchronous demodulator
Power Efficiency of AM: Less than 33%, with most power in the carrier

DSB SC (Double Sideband Suppressed Carrier):
- DSB LC (Large Carrier): Standard AM
- DSB SC: No carrier, only sidebands
SSB (Single Sideband):
- Transmits only one sideband (upper or lower)
- No carrier
VSB (Vestigial Sideband):
- One sideband and a part of the other (vestigial)

DSB LC:
- Carrier and double sidebands (upper and lower)
- Bandwidth: Twice the message bandwidth (2*fm)
DSB SC:
- No carrier
- Power Efficiency: 100%
- Modulation: Multiplication of carrier and message
- Bandwidth: Twice the message bandwidth (same as DSB LC)
- Cannot use envelope detector due to phase reversal
SSB:
- Transmits only one sideband (upper or lower)
- Efficiency: Better power efficiency, less noise, less bandwidth
- More complex modulation and demodulation; requires filters (high-pass or low-pass)
VSB:
- One full sideband and part of the other
- Used mainly for analog TV
- Bandwidth: Between that of SSB and DSB
- Allows reduction in total bandwidth used

DSB LC: AM broadcast for voice and music
- Simple, low-cost receivers
- Examples: AM radios, car radios, AM masts
DSB SC: Used where power efficiency is important
- Examples: Air traffic control, remote controls for garage doors, car fobs
SSB: Used for long-distance voice signals, two-way radios (e.g., taxi radios)
VSB: Analog television (audio using FM and video using VSB)
- Example: TV broadcasting where a high message bandwidth is encountered

Spectrum Analyzer Demonstrations: Shows spectral representations of different AM variants
FFT vs Time Domain: Important to understand both time and frequency domain plots
Real-World Interference Example: Case of signal interference with garage door openers and key fobs due to a custom-made device

AM Variants Recap: DSB LC, DSB SC, SSB, and VSB with their respective applications and complexities
Power and Bandwidth Efficiency: Understand critical trade-offs in terms of power, bandwidth, and simplicity/complexity of modulation/demodulation
Upcoming Focus: Next lecture covers demodulation of DSB SC

Class test on March 17th: Review all six lectures
Next Lecture: Focus on DSB SC demodulation techniques and practical applications