Lecture 7: Angle Modulation (FM and PM)

Recap of Last Lecture: Amplitude Modulation

• Demodulation of Double Sideband Suppressed Carrier (DSB-SC):
  • Introduced the coherent detector (synchronous detector)
  • Components: Local oscillator, multiplier, low pass filter (blocks high frequency components)
  • Discussed frequency and phase errors in the local oscillator

Introduction to Angle Modulation

• Angle Modulation: Modulation of the frequency or phase of a high frequency carrier by the signal amplitude
  • Frequency Modulation (FM) and Phase Modulation (PM)
  • Instantaneous Frequency: New concept where frequency varies instantaneously rather than being constant

Lecture Schedule and Important Dates

• Lecture 8: Demodulation of FM and PM
  • To be recorded on Wednesday, March 17th, 10:00 AM, available on Thursday
• First Class Test: Wednesday, March 17th, worth 15% of the module, no repeat opportunity
  • Covers Lectures 1-6
• Lectures 7 and 8: Not included in the test, FM topics
• Easter Break: Best time to revise for final exams

Angle Modulation: FM and PM

• AM Variants Discussed: AM, DSB-SC, SSB, VSB
• FM Modulation: Frequency varies (high/low) based on message amplitude
• Noise Susceptibility in Modulation:
  • AM: Amplitude variations add noise, more susceptible
  • FM: Constant amplitude, less affected by noise

Comparison of AM and FM

• FM Advantages:
  • Better signal quality due to less noise susceptibility
  • Effective power usage
• FM Disadvantages:
  • Larger bandwidth
  • Shorter range

Mathematical Representations

• Instantaneous Frequency (f_i(t)): Function of time, includes carrier frequency and modulation effect
• Instantaneous Phase (Φ_i(t)): May be a function of message or its integral
• Frequency Deviation (Δf): Maximum deviation from the carrier frequency
• Modulation Index (β for FM): Ratio of Δf to baseband bandwidth
• PM Representation: Consists of a constant amplitude and a varying phase component

FM/PM Properties

• Power in FM/PM: Constant, does not vary with modulation index
• Voltage Controlled Oscillator (VCO): Output frequency proportional to input amplitude

Summary

• Key Takeaways:
  • Difference between FM and PM
  • Modulation index importance
  • Concept of instantaneous frequency and phase
• Next Lecture: Demodulation of FM/PM (Lecture 8)
• Easter Break: Use time for exam preparation

Administrative Notes

• Test: Ensure availability on March 17th; contact if issues arise
• Progress Check: Complete by Sunday