Question
What is the effect of adding a terminating resistor to a rhombic or long-wire antenna?
Answer Options
- A) It reflects the standing waves on the antenna elements back to the transmitter
- B) It changes the radiation pattern from bidirectional to unidirectional
- C) It changes the radiation pattern from horizontal to vertical polarization
- D) It decreases the ground loss
Correct Answer: B
Explanation
An unterminated long wire or rhombic antenna is a standing wave antenna, meaning the signal travels down the wire, hits the open end, and reflects back. This causes the antenna to be bidirectional, radiating effectively off both ends of the wire.
Adding a terminating resistor (usually a non-inductive resistance that matches the antenna’s characteristic impedance, e.g., 600 \Omega) to the far end of the wire absorbs the unradiated power. This absorption prevents the standing wave from forming and eliminates the reflection, forcing the antenna to become a traveling wave antenna. The key effect is that it changes the radiation pattern from bidirectional to unidirectional, concentrating nearly all the energy in one direction.
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