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Introduction to RF Radiation Safety / 3 / 3.10

3.10 REVISION QUESTIONS

  1. Write an equation for an amplitude-modulated (AM) wave.
  2. Sketch the time-domain and frequency-domain diagrams for a 10-V, 10-kHz carrier that has been amplitude modulated by a 2-V, 2-kHz waveform.
  3. Write the equation for an AM modulation factor.
  4. Write the equation for a double-sideband suppressed-carrier (DSB) wave and sketch its time-domain and frequency-domain representations.
  5. Draw the time-domain and frequency-domain representations of the upper-sideband (USB) waveform resulting from a 10-V, 10-kHz carrier modulated by a 2-V, 2-kHz waveform. Draw the lower-sideband (LSB) waveform that would result from the same modulation.
  6. List four advantages of SSB over AM and DSB.
  7. List two disadvantages of SSB compared with DSB.
  8. Briefly describe VSB and ISB.
  9. Briefly describe how the amplitude, polarity and frequency of a modulating waveform affect the carrier in FM.
  10. Write the equation for an FM waveform.
  11. Write the equation for the FM frequency deviation, modulation index and deviation ratio.
  12. Write the equation for Carson’s Law for FM bandwidth.
  13. Briefly describe the FM capture effect.
  14. List four advantages of FM over AM.
  15. Name the most significant disadvantage of wideband FM.
  16. Write the equation for PM.
  17. With the aid of time-domain and frequency-domain diagrams, describe ASK, FSK, PSK, QPSK, APSK, and QAM.
  18. Explain why ASK is rarely used in satellite communications and identify its main vulnerability.
  19. Explain how QPSK achieves twice the bit rate of BPSK without increasing bandwidth.
  20. Describe the difference between PSK and DPSK and why DPSK avoids absolute phase ambiguity.
  21. Compare QPSK, 8PSK, and 16PSK in terms of spectral efficiency and noise tolerance.
  22. Define spectral efficiency.
  23. Explain how modulation depth affects the distribution of power between the carrier and sidebands of a conventional AM signal.
  24. Explain why the total transmitted power of an ideal FM signal remains constant even though power moves between the carrier and sidebands.
  25. Distinguish between constant-envelope and variable-envelope modulation, giving two examples of each and explaining why the distinction matters in RF exposure assessment.
  26. Define peak-to-average power ratio and crest factor, and state the relationship between them under fixed far-field conditions.
  27. A transmitter produces 100 W while active and has a duty cycle of 20%. Calculate its time-averaged power. If the on-state RMS electric field at a measurement point is 50 V/m and the field is zero while the transmitter is inactive, calculate the RMS field over the complete averaging interval.
  28. Explain why an RF exposure instrument's bandwidth, detector type, and averaging time must be appropriate for the modulation being measured.