What is the function of a sense antenna?
The correct answer is A: It modifies the pattern of a DF antenna to provide a null in only one direction. The function of a sense antenna is to modify the pattern of a direction-finding (DF) antenna to provide a null in only one direction. It resolves the bidirectional ambiguity of loop antennas.
A sense antenna is a small omnidirectional antenna (often a short vertical) used with a loop antenna for direction-finding. The loop has bidirectional nulls (two nulls 180 degrees apart). By combining the loop's output with the sense antenna's output in the right phase, you create a cardioid pattern with a single null. This eliminates the ambiguity - you now know which direction the signal is coming from. The sense antenna 'senses' the direction, resolving the bidirectional ambiguity. This is a common technique for improving DF accuracy with loop antennas.
Exam Tip
Sense antenna function = Single null direction. Remember: A sense antenna modifies a DF antenna's pattern to provide a null in only one direction, resolving the bidirectional ambiguity of loop antennas.
Memory Aid
"**S**ense **A**ntenna = **S**ingle **N**ull **D**irection (think 'SA = SND')"
Real-World Application
You're using a loop antenna for direction-finding. The loop has two nulls (bidirectional ambiguity). You add a sense antenna (small vertical) and combine its output with the loop's output. This creates a cardioid pattern with a single null. Now when you find the null, you know exactly which direction the signal is coming from - no ambiguity.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. A sense antenna doesn't increase sensitivity of a DF array. It modifies the pattern to resolve ambiguity, not increase sensitivity.
Option C: Incorrect. A sense antenna doesn't allow receiving at different vertical angles. It's for resolving horizontal direction ambiguity, not elevation.
Option D: Incorrect. A sense antenna doesn't provide diversity reception or cancel multipath. It's specifically for resolving bidirectional null ambiguity in loop antennas.
题目解析
The correct answer is A: It modifies the pattern of a DF antenna to provide a null in only one direction. The function of a sense antenna is to modify the pattern of a direction-finding (DF) antenna to provide a null in only one direction. It resolves the bidirectional ambiguity of loop antennas. A sense antenna is a small omnidirectional antenna (often a short vertical) used with a loop antenna for direction-finding. The loop has bidirectional nulls (two nulls 180 degrees apart). By combining the loop's output with the sense antenna's output in the right phase, you create a cardioid pattern with a single null. This eliminates the ambiguity - you now know which direction the signal is coming from. The sense antenna 'senses' the direction, resolving the bidirectional ambiguity. This is a common technique for improving DF accuracy with loop antennas.
考试技巧
Sense antenna function = Single null direction. Remember: A sense antenna modifies a DF antenna's pattern to provide a null in only one direction, resolving the bidirectional ambiguity of loop antennas.
记忆口诀
**S**ense **A**ntenna = **S**ingle **N**ull **D**irection (think 'SA = SND')
实际应用示例
You're using a loop antenna for direction-finding. The loop has two nulls (bidirectional ambiguity). You add a sense antenna (small vertical) and combine its output with the loop's output. This creates a cardioid pattern with a single null. Now when you find the null, you know exactly which direction the signal is coming from - no ambiguity.
错误选项分析
Option B: Incorrect. A sense antenna doesn't increase sensitivity of a DF array. It modifies the pattern to resolve ambiguity, not increase sensitivity. Option C: Incorrect. A sense antenna doesn't allow receiving at different vertical angles. It's for resolving horizontal direction ambiguity, not elevation. Option D: Incorrect. A sense antenna doesn't provide diversity reception or cancel multipath. It's specifically for resolving bidirectional null ambiguity in loop antennas.
知识点
Sense antenna, Direction-finding, Bidirectional ambiguity, Cardioid pattern
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.