General G3B: MUF, LUF and skip
These are the 12 official questions in group G3B of the 2023–2027 General question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
- G3B01Question 1
What is a characteristic of skywave signals arriving at your location by both short-path and long-path propagation?
- APeriodic fading approximately every 10 seconds
- BSignal strength increased by 3 dB
- CThe signal might be cancelled causing severe attenuation
- DA slightly delayed echo might be heard Correct
Why: Signals arriving by both short and long path can sound like a slight echo.
- G3B02Question 2
What factors affect the MUF?
- APath distance and location
- BTime of day and season
- CSolar radiation and ionospheric disturbances
- DAll these choices are correct Correct
Why: Path distance and direction, time of day and season, and solar activity all affect the MUF. All the choices are correct.
- G3B03Question 3
Which frequency will have the least attenuation for long-distance skip propagation?
- AJust below the MUF Correct
- BJust above the LUF
- CJust below the critical frequency
- DJust above the critical frequency
Why: Just below the MUF has the least attenuation for long-distance skip.
- G3B04Question 4
Which of the following is a way to determine current propagation on a desired band from your station?
- AUse a network of automated receiving stations on the internet to see where your transmissions are being received Correct
- BCheck the A-index
- CSend a series of dots and listen for echoes
- DAll these choices are correct
Why: Automated receiving networks online show where your signal is being heard.
- G3B05Question 5
How does the ionosphere affect radio waves with frequencies below the MUF and above the LUF?
- AThey are refracted back to Earth Correct
- BThey pass through the ionosphere
- CThey are amplified by interaction with the ionosphere
- DThey are refracted and trapped in the ionosphere to circle Earth
Why: Between the LUF and MUF, signals are refracted back to Earth.
- G3B06Question 6
What usually happens to radio waves with frequencies below the LUF?
- AThey are refracted back to Earth
- BThey pass through the ionosphere
- CThey are attenuated before reaching the destination Correct
- DThey are refracted and trapped in the ionosphere to circle Earth
Why: Below the LUF, signals are absorbed before they reach their destination.
- G3B07Question 7
What does LUF stand for?
- AThe Lowest Usable Frequency for communications between two specific points Correct
- BThe Lowest Usable Frequency for communications to any point outside a 100-mile radius
- CThe Lowest Usable Frequency during a 24-hour period
- DThe Lowest Usable Frequency during the past 60 minutes
Why: LUF is the Lowest Usable Frequency between two points.
- G3B08Question 8
What does MUF stand for?
- AThe Minimum Usable Frequency for communications between two points
- BThe Maximum Usable Frequency for communications between two points Correct
- CThe Minimum Usable Frequency during a 24-hour period
- DThe Maximum Usable Frequency during a 24-hour period
Why: MUF is the Maximum Usable Frequency between two points.
- G3B09Question 9
What is the approximate maximum distance along the Earth’s surface normally covered in one hop using the F2 region?
- A180 miles
- B1,200 miles
- C2,500 miles Correct
- D12,000 miles
Why: One F2 hop covers up to about 2,500 miles.
- G3B10Question 10
What is the approximate maximum distance along the Earth’s surface normally covered in one hop using the E region?
- A180 miles
- B1,200 miles Correct
- C2,500 miles
- D12,000 miles
Why: One E-region hop covers up to about 1,200 miles.
- G3B11Question 11
What happens to HF propagation when the LUF exceeds the MUF?
- APropagation via ordinary skywave communications is not possible over that path Correct
- BHF communications over the path are enhanced
- CDouble-hop propagation along the path is more common
- DPropagation over the path on all HF frequencies is enhanced
Why: If the LUF is above the MUF, no frequency works by ordinary skywave on that path.
- G3B12Question 12
Which of the following is typical of the lower HF frequencies during the summer?
- APoor propagation at any time of day
- BWorld-wide propagation during daylight hours
- CHeavy distortion on signals due to photon absorption
- DHigh levels of atmospheric noise or static Correct
Why: Summer brings high atmospheric noise (static) on the lower HF bands.