Amateur Extra E3C: Space weather and propagation tools
These are the 12 official questions in group E3C of the 2024–2028 Amateur Extra 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.
- E3C01Question 1
What is the cause of short-term radio blackouts?
- ACoronal mass ejections
- BSunspots on the solar equator
- CNorth-oriented interplanetary magnetic field
- DSolar flares Correct
Why: Solar flares cause short-term radio blackouts.
- E3C02Question 2
What is indicated by a rising A-index or K-index?
- AIncreasing disturbance of the geomagnetic field Correct
- BDecreasing disturbance of the geomagnetic field
- CHigher levels of solar UV radiation
- DAn increase in the critical frequency
Why: A rising A or K index means growing geomagnetic disturbance.
- E3C03Question 3
Which of the following signal paths is most likely to experience high levels of absorption when the A-index or K-index is elevated?
- ATransequatorial
- BThrough the auroral oval Correct
- CSporadic-E
- DNVIS
Why: Paths through the auroral oval absorb the most when the indices are high.
- E3C04Question 4
What does the value of Bz (B sub z) represent?
- AGeomagnetic field stability
- BCritical frequency for vertical transmissions
- CNorth-south strength of the interplanetary magnetic field Correct
- DDuration of long-delayed echoes
Why: Bz is the north-south strength of the interplanetary magnetic field.
- E3C05Question 5
What orientation of Bz (B sub z) increases the likelihood that charged particles from the Sun will cause disturbed conditions?
- ASouthward Correct
- BNorthward
- CEastward
- DWestward
Why: A southward Bz makes disturbed conditions more likely.
- E3C06Question 6
How does the VHF/UHF radio horizon compare to the geographic horizon?
- AIt is approximately 15 percent farther Correct
- BIt is approximately 20 percent nearer
- CIt is approximately 50 percent farther
- DThey are approximately the same
Why: The VHF/UHF radio horizon is about 15% farther than the geographic horizon.
- E3C07Question 7
Which of the following indicates the greatest solar flare intensity?
- AClass A
- BClass Z
- CClass M
- DClass X Correct
Why: Class X is the most intense flare class.
- E3C08Question 8
Which of the following is the space-weather term for an extreme geomagnetic storm?
- AB9
- BX5
- CM9
- DG5 Correct
Why: G5 is an extreme geomagnetic storm.
- E3C09Question 9
What type of data is reported by amateur radio propagation reporting networks?
- ASolar flux
- BElectric field intensity
- CMagnetic declination
- DDigital-mode and CW signals Correct
Why: Reporting networks collect digital-mode and CW signal reports.
- E3C10Question 10
What does the 304A solar parameter measure?
- AThe ratio of X-ray flux to radio flux, correlated to sunspot number
- BUV emissions at 304 angstroms, correlated to the solar flux index Correct
- CThe solar wind velocity at an angle of 304 degrees from the solar equator, correlated to geomagnetic storms
- DThe solar emission at 304 GHz, correlated to X-ray flare levels
Why: The 304 Å parameter measures solar UV that tracks the solar flux index.
- E3C11Question 11
What does VOACAP software model?
- AAC voltage and impedance
- BVHF radio propagation
- CHF propagation Correct
- DAC current and impedance
Why: VOACAP models HF propagation.
- E3C12Question 12
Which of the following is indicated by a sudden rise in radio background noise across a large portion of the HF spectrum?
- AA temperature inversion has occurred
- BA coronal mass ejection impact or a solar flare has occurred Correct
- CTransequatorial propagation on 6 meters is likely
- DLong-path propagation on the higher HF bands is likely
Why: A sudden rise in noise across HF points to a CME impact or a solar flare.