Sub Element G3: Radio Wave Propagation Flashcards
What is the significance of the sunspot number about HF propagation?
Higher sunspot numbers generally indicate a greater probability of good propagation at higher frequencies
What effect does a Sudden Ionospheric Disturbance have on the daytime ionospheric propagation of HF radio waves?
It disrupts signals on lower frequencies more than those on higher frequencies
Approximately how long does it take the increased ultraviolet and X-ray radiation from solar flares to affect radio propagation on Earth?
8 minutes
Which of the following are least reliable for long-distance communications during periods of low solar activity?
15 meters, 12 meters, and 10 meters
What is the solar flux index?
A measure of solar radiation at 10.7 centimeters wavelength
What is a geomagnetic storm?
A temporary disturbance in Earth’s magnetosphere
At what point in the solar cycle does the 20-meter band usually support worldwide propagation during daylight hours?
At any point in the solar cycle
Which of the following effects can a geomagnetic storm have on radio propagation?
Degraded high-latitude HF propagation
What benefit can high geomagnetic activity have on radio communications?
Auroras that can reflect VHF signals
What causes HF propagation conditions to vary periodically in a roughly 28-day cycle?
The sun’s rotation on its axis
How long does it take charged particles from coronal mass ejections to affect radio propagation on Earth?
20 to 40 hours
What does the A-index indicate?
The long-term stability of Earth’s geomagnetic field
How are radio communications usually affected by the charged particles that reach Earth from solar coronal holes?
HF communications are disturbed
A slightly delayed echo might be heard.
What factors affect the MUF?
Path distance and location
Time of day and season
Solar radiation and ionospheric
disturbances
All these choices are correct
Which of the following applies when selecting a frequency for lowest attenuation when transmitting on HF?
Select a frequency just below the MUF
What is a reliable way to determine if the MUF is high enough to support skip propagation between your station and a distant location on frequencies between 14 and 30 MHz?
Listen for signals from an international beacon in the frequency range you plan to use
What usually happens to radio waves with frequencies below the MUF and above the LUF when they are sent into the ionosphere?
They are bent back to Earth
What usually happens to radio waves with frequencies below the LUF?
They are completely absorbed by the ionosphere
What does LUF stand for?
The Lowest Usable Frequency for communications between two points
What does MUF stand for?
The Maximum Usable Frequency for communications between two points
What is the approximate maximum distance along the Earth’s surface that is normally covered in one hop using the F2 region?
2,500 miles
What is the approximate maximum distance along the Earth’s surface that is normally covered in one hop using the E region?
1,200 miles
What happens to HF propagation when the LUF exceeds the MUF?
No HF radio frequency will support ordinary skywave communications over the path
Which ionospheric layer is closest to the surface of Earth?
The D layer
Where on Earth do ionospheric layers reach their maximum height?
Where the sun is overhead
Why is the F2 region mainly responsible for the longest distance radio wave propagation?
Because it is the highest ionospheric region
What does the term “critical angle” mean, as used in radio wave propagation?
The highest takeoff angle that will return a radio wave to Earth under specific ionospheric conditions
Why is long-distance communication on the 40-meter, 60-meter, 80-meter, and 160- meter bands more difficult during the day?
The D layer absorbs signals at these frequencies during daylight hours
What is a characteristic of HF scatter?
Signals have a fluttering sound
What makes HF scatter signals often sound distorted?
Energy is scattered into the skip zone through several different radio wave paths
Why are HF scatter signals in the skip zone usually weak?
Only a small part of the signal energy is scattered into the skip zone
What type of propagation allows signals to be heard in the transmitting station’s skip zone?
Scatter
What is Near Vertical Incidence Skywave (NVIS) propagation?
Short distance MF or HF propagation using high elevation angles
Which ionospheric layer is the most absorbent of long skip signals during daylight hours on frequencies below 10 MHz?
The D layer
What does the K-index indicate?
The short-term stability of Earth’s magnetic field
