Ham Radio Technician Test Radio Wave Propagation & Modulation 4 — Questions and Answers
Question 1: What is the approximate height of the F2 ionospheric layer above Earth's surface?
- 10–15 km
- 50–90 km
- 200–400 km (Correct answer)
- 600–1000 km
Correct answer: 200–400 km
The F2 layer exists at roughly 200–400 km altitude and is the primary layer responsible for long-distance HF sky wave propagation.
Question 2: What causes 'flutter' in signals received via auroral propagation?
- Rapid changes in transmitter power
- The rapid movement and structure of the aurora causing continuously shifting reflection points (Correct answer)
- Interference from multiple repeaters
- Antenna oscillation in high winds
Correct answer: The rapid movement and structure of the aurora causing continuously shifting reflection points
Aurora-reflected signals exhibit a characteristic flutter or warbling sound because the aurora curtain is constantly moving and the ionized region varies rapidly.
Question 3: Which type of modulation encodes information by varying the frequency of the carrier wave?
- Amplitude modulation (AM)
- Frequency modulation (FM) (Correct answer)
- Phase modulation (PM)
- Pulse-width modulation (PWM)
Correct answer: Frequency modulation (FM)
Frequency modulation (FM) varies the carrier frequency in proportion to the instantaneous amplitude of the modulating audio signal.
Question 4: Why is the 10-meter band generally considered a daytime band during low solar activity?
- The band becomes overcrowded at night
- Without adequate F2 ionization, signals are not refracted back to Earth and pass into space (Correct answer)
- Night-time regulations prohibit 10-meter operation
- The band is used by satellite services at night
Correct answer: Without adequate F2 ionization, signals are not refracted back to Earth and pass into space
During low solar activity, the F2 layer may not be ionized enough to refract 10-meter signals back to Earth, especially at night when solar ionization stops.
Question 5: What is the relationship between frequency and wavelength for radio waves?
- They are directly proportional — higher frequency means longer wavelength
- They are inversely proportional — higher frequency means shorter wavelength (Correct answer)
- They are unrelated
- Wavelength increases with frequency above 30 MHz only
Correct answer: They are inversely proportional — higher frequency means shorter wavelength
Wavelength equals the speed of light divided by frequency; as frequency increases, wavelength decreases proportionally.
Question 6: What does 'over-deviation' cause in an FM transmission?
- The carrier disappears
- Splatter into adjacent channels, causing interference to nearby frequencies (Correct answer)
- The signal becomes weaker
- The audio becomes quieter than normal
Correct answer: Splatter into adjacent channels, causing interference to nearby frequencies
Over-deviation occurs when the FM carrier is shifted too far, causing the signal to spread into adjacent frequency channels and interfere with other users.
Question 7: During a solar flare, what often happens to HF communication on the sunlit side of Earth?
- HF signals improve dramatically due to increased ionization
- HF signals are absorbed by intense D layer ionization, causing a radio blackout (Correct answer)
- HF signals are redirected to the dark side of Earth
- Solar flares only affect VHF and higher frequencies
Correct answer: HF signals are absorbed by intense D layer ionization, causing a radio blackout
Solar flares release intense X-ray radiation that dramatically increases D layer ionization, absorbing HF signals and causing sudden ionospheric disturbances (SIDs) or radio blackouts.
Ham Radio Technician Test Radio Wave Propagation & Modulation 4
What is the approximate height of the F2 ionospheric layer above Earth's surface?