Understanding Single Sideband (SSB)

Introduction

• Objective: Provide a technical introduction to single sideband modulation used in RF communication systems.
• Context: SSB is a special type of amplitude modulation.

Amplitude Modulation (AM) Review

• Creation: Using a mixer with an unmodulated RF carrier and low-frequency modulating signal.
• Time Domain: Modulated RF carrier envelope copies the modulating signal.
• Frequency Domain: Information is in sidebands above and below the carrier.
  • Example: 1000 Hz sine wave creates tones 1000 Hz above and below the carrier.
  • Human speech creates broad, non-uniform sidebands.
• Sidebands: Upper and lower sidebands contain identical information.

Single Sideband Modulation

• Definition: Type of AM where the carrier and one sideband are suppressed.
• Types:
  • Upper Sideband (USB): Suppresses the lower sideband.
  • Lower Sideband (LSB): Suppresses the upper sideband.
• Usage:
  • Mainly for voice transmission; sometimes data.
  • Used primarily at HF, sometimes low VHF.

Advantages of SSB

• Spectral Efficiency: Uses less bandwidth by eliminating half of the signal.
• Power Efficiency: Power focused on one sideband.
• Noise Reduction: Reduced bandwidth decreases received noise.
• Sideband Choice: No inherent advantage; choice usually by convention or agreement.
  • Amateur radio: LSB below 9 MHz, USB above.

Transmission and Reception

• Transmission: Suppresses carrier and one sideband.
• Reception: Requires reinsertion of the carrier using a carrier insertion oscillator (or beat frequency oscillator).
  • Precise frequency reinsertion is crucial for intelligibility.

Variants of SSB

• SSB Suppressed Carrier: Most common.
• SSB Full/Reduced Carrier: Easier reinsertion but less power efficient.
• Independent Sideband: Two sidebands with different information (e.g., early AM stereo).
• Vestigial Sideband: Both sidebands present; one reduced, used in analog TV.

Conclusion

• Benefits of SSB: Less spectrum use, efficient power distribution.
• Challenges: Carrier reinsertion accuracy important for audio quality.
• Variants: Various forms exist to balance ease of reinsertion and power efficiency.
• Applications: From voice and data transmission to specialized broadcast uses.