In antenna systems, a counterpoise (an elevated or radial ground network) is used under which site condition to provide an effective RF ground return?

Introduction / Context:
A counterpoise is a network of wires or radials used to provide a low-impedance RF return when the Earth does not provide a good ground. It is essential for efficient radiation and matched operation of vertical antennas and coils connected to ground in high-resistivity locations.

Given Data / Assumptions:

• Soil conductivity varies with location; deserts and rocky terrains are high resistivity.
• Question asks where counterpoise is used to compensate for poor natural ground.

Concept / Approach:

In high resistivity soil, ground losses are high; RF currents cannot return efficiently via the Earth, increasing system loss and detuning. A counterpoise creates an artificial ground plane close to the antenna feed, reducing loss and stabilizing impedance.

Step-by-Step Solution:

Verification / Alternative check:

Field practice in AM broadcast and HF installations: counterpoises used where soil is poor; over seawater (low resistivity), natural ground is often excellent and counterpoise may be unnecessary.

Why Other Options Are Wrong:

• Low/medium resistivity soils provide acceptable natural ground; counterpoise is not critical.
• Over sea water: natural ground is already excellent; a counterpoise is rarely required.

Common Pitfalls:

Confusing lightning safety grounding (which always benefits from rods) with RF ground return needs; the counterpoise addresses RF, not just DC.

Final Answer:

High resistivity soil (poor natural ground)