Polarization of Man-Made Noise Near the Earth Interference generated by electrical equipment and automobile ignition systems, when observed close to the Earth's surface, is typically:

Introduction / Context:
Receiving antennas often encounter impulsive man-made noise from power lines, motors, and vehicle ignition. Knowing the usual polarization helps select antenna polarization to reduce interference and improve signal-to-noise ratio.

Given Data / Assumptions:

• Observation is near the Earth where many emitters resemble vertical conductors (e.g., wires, leads, vehicle ignition harnesses).
• Local ground effects favor vertical radiation from such structures.
• Receiving systems can choose polarization.

Concept / Approach:

Short vertical wires and monopole-like structures predominantly radiate vertical polarization. Many sources of man-made interference near ground approximate vertical current elements; thus, their radiation near the surface is largely vertically polarized. Horizontal polarization is less common for these incidental emitters.

Step-by-Step Solution:

Verification / Alternative check:

EM measurements near power lines and vehicle ignition systems consistently show stronger coupling to vertically polarized antennas, validating the practical guidance.

Why Other Options Are Wrong:

Horizontal polarization (A) is not the dominant case for these emitters; “not polarized” (D) ignores the structured geometry; circular (E) is not typical of random switching/ignition noise; option C is incomplete/ambiguous.

Common Pitfalls:

Assuming noise is random in polarization; geometry of conductors sets a preferred polarization.

Final Answer:

vertically polarized