Sub Element G3: Radio Wave Propagation

Question 1

What is the significance of the sunspot number about HF propagation?

Answer 1

Higher sunspot numbers generally indicate a greater probability of good propagation at higher frequencies

Question 2

What effect does a Sudden Ionospheric Disturbance have on the daytime ionospheric propagation of HF radio waves?

Answer 2

It disrupts signals on lower frequencies more than those on higher frequencies

Question 3

Approximately how long does it take the increased ultraviolet and X-ray radiation from solar flares to affect radio propagation on Earth?

Answer 3

8 minutes

Question 4

Which of the following are least reliable for long-distance communications during periods of low solar activity?

Answer 4

15 meters, 12 meters, and 10 meters

Question 5

What is the solar flux index?

Answer 5

A measure of solar radiation at 10.7 centimeters wavelength

Question 6

What is a geomagnetic storm?

Answer 6

A temporary disturbance in Earth’s magnetosphere

Question 7

At what point in the solar cycle does the 20-meter band usually support worldwide propagation during daylight hours?

Answer 7

At any point in the solar cycle

Question 8

Which of the following effects can a geomagnetic storm have on radio propagation?

Answer 8

Degraded high-latitude HF propagation

Question 9

What benefit can high geomagnetic activity have on radio communications?

Answer 9

Auroras that can reflect VHF signals

Question 10

What causes HF propagation conditions to vary periodically in a roughly 28-day cycle?

Answer 10

The sun’s rotation on its axis

Question 11

How long does it take charged particles from coronal mass ejections to affect radio propagation on Earth?

Answer 11

20 to 40 hours

Question 12

What does the A-index indicate?

Answer 12

The long-term stability of Earth’s geomagnetic field

Question 13

How are radio communications usually affected by the charged particles that reach Earth from solar coronal holes?

Answer 13

HF communications are disturbed

A slightly delayed echo might be heard.

Question 14

What factors affect the MUF?

Answer 14

Path distance and location

Time of day and season

Solar radiation and ionospheric
disturbances

All these choices are correct

Question 15

Which of the following applies when selecting a frequency for lowest attenuation when transmitting on HF?

Answer 15

Select a frequency just below the MUF

Question 16

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?

Answer 16

Listen for signals from an international beacon in the frequency range you plan to use

Question 17

What usually happens to radio waves with frequencies below the MUF and above the LUF when they are sent into the ionosphere?

Answer 17

They are bent back to Earth

Question 18

What usually happens to radio waves with frequencies below the LUF?

Answer 18

They are completely absorbed by the ionosphere

Question 19

What does LUF stand for?

Answer 19

The Lowest Usable Frequency for communications between two points

Question 20

What does MUF stand for?

Answer 20

The Maximum Usable Frequency for communications between two points

Question 21

What is the approximate maximum distance along the Earth’s surface that is normally covered in one hop using the F2 region?

Answer 21

2,500 miles

Question 22

What is the approximate maximum distance along the Earth’s surface that is normally covered in one hop using the E region?

Answer 22

1,200 miles

Question 23

What happens to HF propagation when the LUF exceeds the MUF?

Answer 23

No HF radio frequency will support ordinary skywave communications over the path

Question 24

Which ionospheric layer is closest to the surface of Earth?

Answer 24

The D layer

Question 25

Where on Earth do ionospheric layers reach their maximum height?

Answer 25

Where the sun is overhead

Question 26

Why is the F2 region mainly responsible for the longest distance radio wave propagation?

Answer 26

Because it is the highest ionospheric region

Question 27

What does the term “critical angle” mean, as used in radio wave propagation?

Answer 27

The highest takeoff angle that will return a radio wave to Earth under specific ionospheric conditions

Question 28

Why is long-distance communication on the 40-meter, 60-meter, 80-meter, and 160- meter bands more difficult during the day?

Answer 28

The D layer absorbs signals at these frequencies during daylight hours

Question 29

What is a characteristic of HF scatter?

Answer 29

Signals have a fluttering sound

Question 30

What makes HF scatter signals often sound distorted?

Answer 30

Energy is scattered into the skip zone through several different radio wave paths

Question 31

Why are HF scatter signals in the skip zone usually weak?

Answer 31

Only a small part of the signal energy is scattered into the skip zone

Question 32

What type of propagation allows signals to be heard in the transmitting station’s skip zone?

Answer 32

Scatter

Question 33

What is Near Vertical Incidence Skywave (NVIS) propagation?

Answer 33

Short distance MF or HF propagation using high elevation angles

Question 34

Which ionospheric layer is the most absorbent of long skip signals during daylight hours on frequencies below 10 MHz?

Answer 34

The D layer

Question 35

What does the K-index indicate?

Answer 35

The short-term stability of Earth’s magnetic field