Radio Wave PropagationRadio Telephony — DGCA CPL practice questions
Question 1 of 16
An NDB relies mainly on which propagation path?
All 16 questions — Radio Wave Propagation
Radio Telephony · DGCA CPL. The correct option is marked on each.
Q1. An NDB relies mainly on which propagation path?
- A.Ground (surface) wave✓
- B.Sky wave
- C.Space wave
- D.Satellite
Why: NDB (LF/MF) uses the ground wave that follows the Earth's curvature.
Q2. Ground-wave range is greatest over:
- A.Dry desert
- B.Sea water (high conductivity)✓
- C.Mountains
- D.Forest
Why: Higher surface conductivity (sea) gives much greater ground-wave range.
Q3. Long-range HF communication is achieved by:
- A.Ground wave
- B.Sky wave refracted by the ionosphere✓
- C.Line-of-sight space wave
- D.Direct wave only
Why: HF sky waves refract off the ionosphere to travel thousands of miles.
Q4. Which ionospheric layer absorbs lower HF frequencies by day?
- A.D layer✓
- B.E layer
- C.F1 layer
- D.F2 layer
Why: layer. The D layer forms by day and absorbs lower frequencies; it disappears at night.
Q5. For HF, the best night-time frequency compared with daytime is generally:
- A.Higher
- B.Lower✓
- C.The same
- D.Zero
Why: The D layer disappears at night, so a lower frequency works best — "day high, night low."
Q6. A frequency above the MUF will:
- A.Be absorbed by the D layer
- B.Pass through the ionosphere into space✓
- C.Follow the ground
- D.Always reflect
Why: Above the Maximum Usable Frequency the wave is no longer refracted back — it escapes to space.
Q7. The optimum working frequency (OWF) is typically about:
- A.50% of the MUF
- B.85% of the MUF✓
- C.110% of the MUF
- D.Equal to the LUF
Why: The OWF is set around 85% of the MUF so variation doesn't push it above the MUF.
Q8. The silent ring between ground-wave coverage and the first returning sky wave is the:
- A.Skip distance
- B.Dead space (skip zone)✓
- C.Radio horizon
- D.Fading zone
Why: ead space (skip zone). Dead space is the gap where neither ground nor sky wave is received.
Q9. Skip distance generally increases when:
- A.Frequency is lowered
- B.Frequency is raised toward the MUF / at night✓
- C.Power is reduced
- D.The antenna is shortened
Why: Higher frequency and a weaker (night) ionosphere lengthen the skip distance.
Q10. The line-of-sight range from 10,000 ft is approximately:
- A.12 NM
- B.123 NM✓
- C.1230 NM
- D.40 NM
Why: d ≈ 1.23 × √10,000 = 1.23 × 100 = 123 NM.
Q11. VHF reception is lost behind a hill on approach. This is:
- A.Sky-wave fading
- B.Skip distance
- C.Ground shadow✓
- D.Absorption by the D layer
Why: Terrain blocking the line-of-sight (space) wave creates a ground shadow.
Q12. Fading on an HF signal is usually caused by:
- A.High transmitter power
- B.Two paths interfering (e.g. ground + sky, or two sky paths)✓
- C.A short antenna
- D.Vertical polarization
Why: Fading is interference between signals arriving by different paths, common on HF.
Q13. The ionosphere's ionisation varies with:
- A.Transmitter power only
- B.Time of day, season and the 11-year solar cycle✓
- C.Antenna length
- D.Aircraft altitude
Why: It is driven by the Sun, so it varies diurnally, seasonally and with the sunspot cycle.
Q14. A sky wave can reach right around the world by:
- A.Following the ground
- B.Multiple hops between the ionosphere and the ground✓
- C.Travelling in a straight line
- D.Using a satellite
Why: Repeated refraction and ground reflection make multiple hops possible.
Q15. The radio horizon is, compared with the visual horizon:
- A.Shorter
- B.Slightly farther (atmospheric refraction)✓
- C.Exactly the same
- D.Half as far
Why: Atmospheric refraction bends the wave slightly, extending the radio horizon a little beyond the visual one.
Q16. Which path does VHF ATC voice use?
- A.Ground wave
- B.Sky wave
- C.Space wave (line-of-sight)✓
- D.All three equally
Why: VHF uses the space wave — line-of-sight, range growing with altitude.