Ham Radio General Class Test Radio Wave Propagation 2 — Questions and Answers
Question 1: What is the primary cause of sky-wave propagation on HF bands?
- Reflection from the ground
- Refraction by the ionosphere (Correct answer)
- Diffraction around obstacles
- Absorption by the troposphere
Correct answer: Refraction by the ionosphere
Sky-wave propagation occurs when HF signals are refracted (bent) back to Earth by the ionized layers of the ionosphere.
Question 2: Which ionospheric layer is primarily responsible for long-distance HF propagation during daylight hours?
- D layer
- E layer
- F1 layer
- F2 layer (Correct answer)
Correct answer: F2 layer
The F2 layer, located at roughly 200-400 km altitude, provides the longest skip distances and is the primary layer for HF DX propagation.
Question 3: What is 'gray line' propagation?
- Propagation caused by industrial interference zones
- Enhanced propagation along the terminator between daylight and darkness (Correct answer)
- Propagation through stratified clouds
- Weak signal propagation through urban areas
Correct answer: Enhanced propagation along the terminator between daylight and darkness
The gray line (terminator) is the boundary between day and night where the D layer is absent but F layer ionization remains, enabling enhanced propagation.
Question 4: What effect does a sudden ionospheric disturbance (SID) have on HF communications?
- It enhances all HF propagation for several hours
- It causes short-skip conditions on 10 meters
- It absorbs HF signals on the sunlit side of Earth, causing a radio blackout (Correct answer)
- It shifts the MUF upward by 20-30 MHz
Correct answer: It absorbs HF signals on the sunlit side of Earth, causing a radio blackout
A SID is caused by a solar X-ray flare that dramatically increases D-layer ionization, absorbing HF signals on the Earth's sunlit side.
Question 5: What is 'transequatorial propagation' (TEP)?
- Propagation only possible below 10 MHz across the equator
- Propagation via F layer ionization across the magnetic equator, often reaching 50 MHz or above (Correct answer)
- Ground-wave propagation along the equator
- Scatter propagation caused by equatorial rain
Correct answer: Propagation via F layer ionization across the magnetic equator, often reaching 50 MHz or above
TEP is a mode where signals propagate via enhanced F layer ionization on both sides of the magnetic equator and can extend into VHF frequencies.
Question 6: How does increasing solar flux affect the Maximum Usable Frequency (MUF)?
- Higher solar flux lowers the MUF by absorbing HF energy
- Higher solar flux raises the MUF by increasing ionospheric ionization (Correct answer)
- Solar flux has no effect on MUF
- Higher solar flux only affects frequencies below 10 MHz
Correct answer: Higher solar flux raises the MUF by increasing ionospheric ionization
Greater solar flux produces more ionization in the F layer, which raises the critical frequency and therefore increases the MUF for a given path.
Question 7: What is 'auroral propagation' and on which bands is it most common?
- Smooth, quiet propagation near the poles on 160 meters
- Distorted, flutter-type signals scattered by the aurora on VHF bands like 6 meters and 2 meters (Correct answer)
- Enhanced skip on 40 meters caused by geomagnetic storms
- Line-of-sight propagation enhanced by northern lights
Correct answer: Distorted, flutter-type signals scattered by the aurora on VHF bands like 6 meters and 2 meters
Auroral propagation occurs when VHF signals scatter off the ionized curtain of the aurora borealis, producing characteristic fluttery, distorted audio.
Ham Radio General Class Test Radio Wave Propagation 2
What is the primary cause of sky-wave propagation on HF bands?