General G3A: The Sun and HF propagation
These are the 14 official questions in group G3A 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.
- G3A01Question 1
How does a higher sunspot number affect HF propagation?
- AHigher sunspot numbers generally indicate a greater probability of good propagation at higher frequencies Correct
- BLower sunspot numbers generally indicate greater probability of sporadic E propagation
- CA zero sunspot number indicates that radio propagation is not possible on any band
- DA zero sunspot number indicates undisturbed conditions
Why: More sunspots ionize the ionosphere more, so the higher HF bands open more often.
- G3A02Question 2
What effect does a sudden ionospheric disturbance have on the daytime ionospheric propagation?
- AIt enhances propagation on all HF frequencies
- BIt disrupts signals on lower frequencies more than those on higher frequencies Correct
- CIt disrupts communications via satellite more than direct communications
- DNone, because only areas on the night side of the Earth are affected
Why: A sudden ionospheric disturbance hits lower frequencies harder than higher ones.
- G3A03Question 3
Approximately how long does it take the increased ultraviolet and X-ray radiation from a solar flare to affect radio propagation on Earth?
- A28 days
- B1 to 2 hours
- C8 minutes Correct
- D20 to 40 hours
Why: Flare radiation travels at the speed of light, about 8 minutes from the Sun.
- G3A04Question 4
Which of the following are the least reliable bands for long-distance communications during periods of low solar activity?
- A80 meters and 160 meters
- B60 meters and 40 meters
- C30 meters and 20 meters
- D15 meters, 12 meters, and 10 meters Correct
Why: With low solar activity, 15, 12 and 10 meters are least reliable for long distance.
- G3A05Question 5
What is the solar flux index?
- AA measure of the highest frequency that is useful for ionospheric propagation between two points on Earth
- BA count of sunspots that is adjusted for solar emissions
- CAnother name for the American sunspot number
- DA measure of solar radiation with a wavelength of 10.7 centimeters Correct
Why: The solar flux index measures solar radio output at 10.7 cm wavelength.
- G3A06Question 6
What is a geomagnetic storm?
- AA sudden drop in the solar flux index
- BA thunderstorm that affects radio propagation
- CRipples in the geomagnetic force
- DA temporary disturbance in Earth’s geomagnetic field Correct
Why: A geomagnetic storm is a temporary disturbance in Earth's magnetic field.
- G3A07Question 7
At what point in the solar cycle does the 20-meter band usually support worldwide propagation during daylight hours?
- AAt the summer solstice
- BOnly at the maximum point
- COnly at the minimum point
- DAt any point Correct
Why: 20 meters usually supports worldwide daylight contacts at any point in the solar cycle.
- G3A08Question 8
How can a geomagnetic storm affect HF propagation?
- AImprove high-latitude HF propagation
- BDegrade ground wave propagation
- CImprove ground wave propagation
- DDegrade high-latitude HF propagation Correct
Why: Geomagnetic storms degrade high-latitude HF paths.
- G3A09Question 9
How can high geomagnetic activity benefit radio communications?
- ACreates auroras that can reflect VHF signals Correct
- BIncreases signal strength for HF signals passing through the polar regions
- CImprove HF long path propagation
- DReduce long delayed echoes
Why: High geomagnetic activity creates auroras that can reflect VHF signals.
- G3A10Question 10
What causes HF propagation conditions to vary periodically in a 26- to 28-day cycle?
- ALong term oscillations in the upper atmosphere
- BCyclic variation in Earth’s radiation belts
- CRotation of the Sun’s surface layers around its axis Correct
- DThe position of the Moon in its orbit
Why: The Sun rotates about every 27 days, bringing active regions back into view.
- G3A11Question 11
How long does it take a coronal mass ejection to affect radio propagation on Earth?
- A28 days
- B14 days
- C4 to 8 minutes
- D15 hours to several days Correct
Why: A coronal mass ejection takes 15 hours to several days to reach Earth.
- G3A12Question 12
What does the K-index measure?
- AThe relative position of sunspots on the surface of the Sun
- BThe short-term stability of Earth’s geomagnetic field Correct
- CThe short-term stability of the Sun’s magnetic field
- DThe solar radio flux at Boulder, Colorado
Why: The K-index measures short-term geomagnetic stability.
- G3A13Question 13
What does the A-index measure?
- AThe relative position of sunspots on the surface of the Sun
- BThe amount of polarization of the Sun’s electric field
- CThe long-term stability of Earth’s geomagnetic field Correct
- DThe solar radio flux at Boulder, Colorado
Why: The A-index measures long-term geomagnetic stability.
- G3A14Question 14
How is long distance radio communication usually affected by the charged particles that reach Earth from solar coronal holes?
- AHF communication is improved
- BHF communication is disturbed Correct
- CVHF/UHF ducting is improved
- DVHF/UHF ducting is disturbed
Why: Particles from coronal holes disturb HF communication.