Ham Radio Technician Test Radio Wave Propagation & Modulation 2 — Questions and Answers
Question 1: What effect does a temperature inversion in the atmosphere have on VHF radio waves?
- It completely absorbs VHF signals
- It can cause signals to travel much farther than normal (Correct answer)
- It reflects VHF back into space
- It converts VHF to HF frequencies
Correct answer: It can cause signals to travel much farther than normal
Temperature inversions can trap VHF signals near the Earth's surface, allowing them to travel far beyond the normal line-of-sight distance through ducting.
Question 2: Which modulation mode is most commonly used for FM voice transmissions on VHF/UHF amateur bands?
- Single sideband (SSB)
- Amplitude modulation (AM)
- Frequency modulation (FM) (Correct answer)
- Continuous wave (CW)
Correct answer: Frequency modulation (FM)
FM is the standard mode for local VHF/UHF voice repeater operation because it provides good audio quality and rejects noise effectively.
Question 3: What is the term for the lowest frequency that will be refracted back to Earth from the ionosphere at vertical incidence?
- Maximum usable frequency (MUF)
- Critical frequency (Correct answer)
- Skip frequency
- Lowest usable frequency (LUF)
Correct answer: Critical frequency
The critical frequency is the highest frequency that is refracted back to Earth when a signal is transmitted straight up (vertical incidence).
Question 4: Which ionospheric layer is primarily responsible for long-distance HF communication during daytime?
- D layer
- E layer
- F1 layer
- F2 layer (Correct answer)
Correct answer: F2 layer
The F2 layer, found at 200–400 km altitude, is the most important layer for long-distance HF propagation because it persists day and night.
Question 5: What type of propagation allows a 10-meter signal to be received across the country with very low power during high solar activity?
- Ground wave propagation
- Sporadic-E propagation
- F2 ionospheric propagation (Correct answer)
- Tropospheric ducting
Correct answer: F2 ionospheric propagation
During periods of high solar activity, F2 layer ionization is strong enough to refract 10-meter signals back to Earth over very long distances.
Question 6: What is the deviation in an FM signal?
- The rate at which the carrier frequency changes
- The amount the carrier frequency shifts above and below its center frequency (Correct answer)
- The ratio of modulating signal amplitude to carrier amplitude
- The bandwidth occupied by the sidebands
Correct answer: The amount the carrier frequency shifts above and below its center frequency
Deviation is the maximum shift of the carrier frequency above and below the resting center frequency, determined by the amplitude of the modulating audio signal.
Question 7: Which band is most likely to support auroral propagation?
- 160 meters
- 40 meters
- 2 meters (Correct answer)
- 630 meters
Correct answer: 2 meters
Auroral propagation primarily occurs on VHF bands, especially 2 meters (144 MHz), where signals are reflected off the ionized curtain of the aurora borealis.
Ham Radio Technician Test Radio Wave Propagation & Modulation 2
What effect does a temperature inversion in the atmosphere have on VHF radio waves?