Communications Fundamentals FAQ

Chapter 9 FAQ

1. 9.16.1 What Does a Radio Transmitter Actually Do
   1. What Is a Radio Transmitter?
   2. Why Is a Carrier Needed?
   3. What Are the Main Functions of a Transmitter?
   4. What Is Frequency Translation?
   5. What Is Modulation?
   6. Why Must the Signal Be Amplified?
   7. Why Can't Transmitters Simply Increase Power Indefinitely?
   8. Why Is Frequency Stability So Important?
   9. How Are Stable Frequencies Generated?
   10. Why Must Unwanted Signals Be Suppressed?
   11. What Is Spectral Purity?
   12. Why Is Linearity Important?
   13. What Is Digital Predistortion?
   14. How Have Software-Defined Radios Changed Transmitters?
   15. What Happens Immediately Before Transmission?
   16. Where Are Radio Transmitters Used?
   17. How Have Transmitters Changed Since the Early Days of Radio?
   18. Why Is the Transmitter Only Half of the Communication System?
2. 9.16.2 How Does a Radio Receiver Recover Information from Radio Waves
   1. What Is a Radio Receiver?
   2. Why Is Receiving More Difficult Than Transmitting?
   3. What Happens First?
   4. Why Is the First Amplifier So Important?
   5. What Is Receiver Sensitivity?
   6. What Limits Sensitivity?
   7. What Is Noise Figure?
   8. Why Must Receivers Reject Other Signals?
   9. What Is Selectivity?
   10. Why Is Frequency Conversion Used?
   11. What Is Demodulation?
   12. What Happens After Demodulation?
   13. Why Are Modern Receivers Increasingly Digital?
   14. How Do Receivers Handle Very Strong Signals?
   15. What Is Dynamic Range?
   16. How Do Receivers Cope with Multipath?
   17. Where Are Radio Receivers Used?
   18. How Have Receivers Changed Over Time?
   19. Why Is the Receiver Only Half of the Communication System?
3. 9.16.3 Why Did Radio Receivers Evolve from Crystal Sets to Superheterodyne Receivers
   1. What Were the First Radio Receivers Like?
   2. What Was a Crystal Receiver?
   3. What Were the Limitations of Crystal Receivers?
   4. What Is a Tuned Radio-Frequency (TRF) Receiver?
   5. Why Was the TRF Receiver an Improvement?
   6. Why Did TRF Receivers Become Difficult to Design?
   7. What Was the Regenerative Receiver?
   8. What Were the Disadvantages of Regeneration?
   9. What Is the Heterodyne Principle?
   10. Why Is Frequency Conversion Useful?
   11. Who Invented the Superheterodyne Receiver?
   12. Why Did the Superheterodyne Replace Earlier Designs?
   13. Did Older Receiver Types Disappear Immediately?
   14. How Did Transistors Change Receiver Design?
   15. What Happened After Integrated Circuits?
   16. How Have Digital Technologies Changed Receivers?
   17. What Is a Software-Defined Radio?
   18. Why Is the Evolution Still Continuing?
   19. What Is the Most Important Lesson from This Evolution?
4. 9.16.4 Why Is the Superheterodyne Receiver One of the Most Important Inventions in Communications
   1. What Is a Superheterodyne Receiver?
   2. Why Is It Called "Superheterodyne"?
   3. What Is Frequency Conversion?
   4. What Is the Local Oscillator?
   5. What Is the Intermediate Frequency?
   6. Why Use an Intermediate Frequency?
   7. How Does the Receiver Tune Different Stations?
   8. Why Is This Better Than a TRF Receiver?
   9. What Is Selectivity?
   10. What Is Image Frequency?
   11. How Are Image Signals Rejected?
   12. Why Are Some Receivers Double Conversion?
   13. What Is Triple Conversion?
   14. Why Was the Superheterodyne So Successful?
   15. Were There Any Disadvantages?
   16. Is the Superheterodyne Still Used Today?
   17. How Have Software-Defined Radios Changed the Architecture?
   18. Why Is Armstrong's Invention Still Important?
5. 9.16.5 Why Are Frequency Synthesizers Used Instead of Crystal Oscillators
   1. Why Is Frequency Stability So Important?
   2. What Is a Crystal Oscillator?
   3. Why Can't One Crystal Generate Every Frequency?
   4. What Is a Frequency Synthesizer?
   5. How Does a Frequency Synthesizer Work?
   6. What Is a Phase-Locked Loop?
   7. What Are the Main Parts of a PLL?
   8. What Is a Voltage-Controlled Oscillator?
   9. What Is Direct Digital Synthesis?
   10. How Does DDS Compare with PLL?
   11. What Is Phase Noise?
   12. What Is Frequency Accuracy?
   13. What Is Frequency Stability?
   14. What Is a TCXO?
   15. What Is an OCXO?
   16. What Is a GPS-Disciplined Oscillator?
   17. Where Are Frequency Synthesizers Used?
   18. Why Are Fast Frequency Changes Important?
   19. How Have Synthesizers Changed Radio Design?
   20. Why Are Frequency Synthesizers Important?
6. 9.16.6 What Determines How Sensitive a Radio Receiver Is
   1. What Is Receiver Sensitivity?
   2. Why Is High Sensitivity Important?
   3. What Limits Receiver Sensitivity?
   4. What Is Thermal Noise?
   5. Why Is Thermal Noise Often Expressed as –174 dBm/Hz?
   6. Why Does Bandwidth Affect Noise?
   7. What Is the Noise Floor?
   8. What Is Noise Figure?
   9. Why Is the First Amplifier So Important?
   10. What Is a Low-Noise Amplifier?
   11. Why Are Satellite LNAs Mounted Near the Antenna?
   12. Why Are Some Receivers Cooled?
   13. What Is Signal-to-Noise Ratio?
   14. What Is Dynamic Range?
   15. Why Can Strong Signals Be a Problem?
   16. What Is Receiver Blocking?
   17. What Is Intermodulation?
   18. Can Digital Signal Processing Improve Sensitivity?
   19. Where Is High Receiver Sensitivity Most Important?
   20. Why Is Receiver Sensitivity Important?
7. 9.16.7 Why Must Radio Receivers Reject Unwanted Signals
   1. What Is Receiver Selectivity?
   2. Why Is Selectivity Important?
   3. Isn't Tuning Enough?
   4. What Is a Filter?
   5. Why Are Band-Pass Filters So Important?
   6. What Is Adjacent-Channel Interference?
   7. What Is Co-Channel Interference?
   8. What Is Image Frequency?
   9. How Are Image Frequencies Rejected?
   10. What Is Receiver Blocking?
   11. What Is Desensitization?
   12. What Is Intermodulation?
   13. Why Is the Receiver Front End So Important?
   14. What Is Dynamic Range?
   15. How Does Digital Signal Processing Improve Selectivity?
   16. What Is Adaptive Filtering?
   17. Why Is Narrower Bandwidth Often Better?
   18. Where Is Excellent Selectivity Most Important?
   19. Why Are Modern Receivers Better Than Earlier Designs?
8. 9.16.8 What Is Automatic Gain Control (AGC) and Why Is It Needed
   1. What Is Automatic Gain Control?
   2. Why Is AGC Necessary?
   3. What Does "Gain" Mean?
   4. How Does AGC Work?
   5. Where Is the Signal Measured?
   6. Does AGC Increase Weak Signals?
   7. Can AGC Improve Receiver Sensitivity?
   8. Why Must AGC Reduce Strong Signals?
   9. What Is AGC Attack Time?
   10. What Is Release Time?
   11. Why Not Make AGC Instantaneous?
   12. What Is AGC Pumping?
   13. Is AGC Used in Digital Receivers?
   14. What Is Fast AGC?
   15. What Is Slow AGC?
   16. What Is Squelch?
   17. What Is Carrier Squelch?
   18. What Is Tone Squelch?
   19. Does AGC Work with Modern Modulation?
   20. What Are the Advantages of AGC?
   21. Are There Any Limitations?
   22. Why Is Automatic Gain Control Important?
9. 9.16.9 What Is Software-Defined Radio (SDR), and Why Has It Changed Communications
   1. What Is Software-Defined Radio?
   2. Why Is It Called Software-Defined Radio?
   3. How Does an SDR Differ from a Traditional Radio?
   4. Does an SDR Eliminate All Hardware?
   5. What Is an Analogue-to-Digital Converter?
   6. What Is a Digital-to-Analogue Converter?
   7. What Is Digital Signal Processing?
   8. What Is Digital Down-Conversion?
   9. What Is Digital Up-Conversion?
   10. What Is an FPGA?
   11. What Is a General-Purpose Processor?
   12. Why Is SDR So Flexible?
   13. Can SDR Be Updated?
   14. Where Is SDR Used?
   15. Why Is SDR Important for the Military?
   16. How Has SDR Changed Satellite Communications?
   17. Is SDR Used in Mobile Networks?
   18. Are There Any Disadvantages?
   19. What Is Cognitive Radio?
   20. Will Future Radios Be Entirely Software Defined?
   21. Why Has SDR Been Such a Revolutionary Development?
10. 9.16.10 What Will the Radio Transmitters and Receivers of the Future Look Like
    1. Will Radios Continue to Become More Digital?
    2. What Is Direct RF Sampling?
    3. Why Is Direct RF Sampling Becoming Practical?
    4. What Is Cognitive Radio?
    5. How Does Artificial Intelligence Help?
    6. What Is Machine Learning?
    7. What Is Digital Beamforming?
    8. What Is Massive MIMO?
    9. What Is Integrated Sensing and Communications?
    10. Will Satellites Become More Flexible?
    11. What Is an Intelligent Reflecting Surface?
    12. Will Radios Become More Energy Efficient?
    13. How Will Security Change?
    14. What Is Quantum Communication?
    15. Will 6G Change Radio Design?
    16. Will Hardware Eventually Become Less Important?
    17. What Skills Will Future Communications Engineers Need?
    18. What Is the Future of Radio?