Updated: Dec 9, 2025 | Source: 2024-2028 Question Pool | Topic: E3C
E3C12E3C

Which of the following is indicated by a sudden rise in radio background noise across a large portion of the HF spectrum?

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Deep Dive: E3C12

The correct answer is B: A coronal mass ejection impact or a solar flare has occurred. Which of the following is indicated by a sudden rise in radio background noise across a large portion of the HF spectrum is a coronal mass ejection impact or a solar flare has occurred. Sudden noise increases indicate solar events. For amateur radio operators, this is important for understanding propagation disruptions. Understanding this helps when experiencing noise increases.

Why Other Answers Are Wrong

Option A: Incorrect. Temperature inversion doesn't cause sudden HF noise rise - solar events do. Temperature inversion isn't the cause. Option C: Incorrect. Transequatorial propagation on 6 meters isn't indicated - solar events are indicated. TEP on 6m isn't the indication. Option D: Incorrect. Long-path propagation on higher HF bands isn't indicated - solar events are indicated. Long-path isn't the indication.

Exam Tip

Sudden HF noise rise = coronal mass ejection impact or solar flare occurred. Think 'S'udden 'N'oise = 'S'olar 'N'oise. Sudden noise increases across HF spectrum indicate solar events. Not temperature inversion, not TEP, not long-path - just solar events.

Memory Aid

Sudden HF noise rise = coronal mass ejection impact or solar flare occurred. Think 'S'udden 'N'oise = 'S'olar event. Sudden noise increases across HF spectrum indicate solar events. Important for understanding propagation disruptions.

Real-World Example

A sudden rise in radio background noise across a large portion of the HF spectrum: It indicates that a coronal mass ejection impact or a solar flare has occurred. These solar events create ionization that increases noise levels. This is the indication - solar events cause sudden noise increases.

Source & Coverage

Question Pool: 2024-2028 Question Pool

Subelement: E3C

Reference: 2024-2028 Question Pool · E3 - Radio Wave Propagation

Key Concepts

Sudden rise in radio background noise Large portion of HF spectrum Coronal mass ejection Solar flare

Verified Content

Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E3C topic.