Question
What is the function of a sense antenna?
Answer Options
- A) It modifies the pattern of a DF antenna to provide a null in only one direction
- B) It increases the sensitivity of a DF antenna array
- C) It allows DF antennas to receive signals at different vertical angles
- D) It provides diversity reception that cancels multipath signals
Correct Answer: A
Explanation
A directional finding (DF) antenna like a loop typically has a bidirectional pattern (e.g., a figure-eight pattern with nulls at 90° and 270°), making it impossible to determine the signal’s direction without a 180° ambiguity. To resolve this, a separate, omnidirectional antenna is introduced.
A sense antenna (typically a vertical whip with an omnidirectional pattern) is used to modify the pattern of a DF antenna to provide a null in only one direction. By mixing the loop antenna’s signal with the sense antenna’s signal (which has no nulls), the resulting pattern is a unidirectional cardioid (heart shape), allowing the operator to eliminate the 180° ambiguity.
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