G3C – Ionospheric regions; critical angle and frequency; HF scatter; near vertical incidence skywave (NVIS)

- [[G3C01]] (A)
Which ionospheric region is closest to the surface of Earth? #card
	- A. The D region
	- B. The E region
	- C. The F1 region
	- D. The F2 region
- [[G3C02]] (A)
What is meant by the term “critical frequency” at a given incidence angle? #card
	- A. The highest frequency which is refracted back to Earth
	- B. The lowest frequency which is refracted back to Earth
	- C. The frequency at which the signal-to-noise ratio approaches unity
	- D. The frequency at which the signal-to-noise ratio is 6 dB
- [[G3C03]] (C)
Why is skip propagation via the F2 region longer than that via the other ionospheric regions? #card
	- A. Because it is the densest
	- B. Because of the Doppler effect
	- C. Because it is the highest
	- D. Because of temperature inversions
- [[G3C04]] (D)
What does the term “critical angle” mean, as applied to radio wave propagation? #card
	- A. The long path azimuth of a distant station
	- B. The short path azimuth of a distant station
	- C. The lowest takeoff angle that will return a radio wave to Earth under specific ionospheric conditions
	- D. The highest takeoff angle that will return a radio wave to Earth under specific ionospheric conditions
- [[G3C05]] (C)
Why is long-distance communication on the 40-, 60-, 80-, and 160-meter bands more difficult during the day? #card
	- A. The F region absorbs signals at these frequencies during daylight hours
	- B. The F region is unstable during daylight hours
	- C. The D region absorbs signals at these frequencies during daylight hours
	- D. The E region is unstable during daylight hours
- [[G3C06]] (B)
What is a characteristic of HF scatter? #card
	- A. Phone signals have high intelligibility
	- B. Signals have a fluttering sound
	- C. There are very large, sudden swings in signal strength
	- D. Scatter propagation occurs only at night
- [[G3C07]] (D)
What makes HF scatter signals often sound distorted? #card
	- A. The ionospheric region involved is unstable
	- B. Ground waves are absorbing much of the signal
	- C. The E region is not present
	- D. Energy is scattered into the skip zone through several different paths
- [[G3C08]] (A)
Why are HF scatter signals in the skip zone usually weak? #card
	- A. Only a small part of the signal energy is scattered into the skip zone
	- B. Signals are scattered from the magnetosphere, which is not a good reflector
	- C. Propagation is via ground waves, which absorb most of the signal energy
	- D. Propagation is via ducts in the F region, which absorb most of the energy
- [[G3C09]] (B)
What type of propagation allows signals to be heard in the transmitting station’s skip zone? #card
	- A. Faraday rotation
	- B. Scatter
	- C. Chordal hop
	- D. Short-path
- [[G3C10]] (B)
What is near vertical incidence skywave (NVIS) propagation? #card
	- A. Propagation near the MUF
	- B. Short distance MF or HF propagation at high elevation angles
	- C. Long path HF propagation at sunrise and sunset
	- D. Double hop propagation near the LUF
- [[G3C11]] (D)
Which ionospheric region is the most absorbent of signals below 10 MHz during daylight hours? #card
	- A. The F2 region
	- B. The F1 region
	- C. The E region
	- D. The D region