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How does the energy content of atmospheric noise vary with frequency?

Difficulty: Easy

Correct Answer: decreases as frequency is increased

Explanation:


Introduction / Context:
Atmospheric noise arises due to lightning discharges and other natural processes. It plays a role in determining radio link design, particularly in HF and VHF bands.


Given Data / Assumptions:

  • Noise sources: natural (lightning, cosmic noise).
  • Observed across radio frequencies.


Concept / Approach:
Atmospheric noise power is inversely related to frequency. At lower frequencies, noise is dominant; at higher frequencies, thermal and man-made noise dominate.


Step-by-Step Solution:

At LF/MF (~30 kHz–3 MHz): atmospheric noise dominates.At HF/VHF and above: atmospheric noise decreases rapidly with frequency.Thus, energy content decreases as frequency increases.


Verification / Alternative check:
ITU noise curves (P.372) confirm steep decline of atmospheric noise beyond a few MHz.


Why Other Options Are Wrong:

Independence or increase with frequency contradicts experimental evidence.Temperature has minor effect, not a deciding factor here.


Common Pitfalls:

Confusing atmospheric noise with thermal noise (which is flat).


Final Answer:

decreases as frequency is increased
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