What is receiving directivity factor (RDF)?
The correct answer is D: Peak antenna gain compared to average gain over the hemisphere around and above the antenna. Receiving directivity factor (RDF) is peak antenna gain compared to average gain over the hemisphere around and above the antenna. It measures how much the antenna concentrates reception in specific directions.
RDF compares the peak gain (in the best direction) to the average gain over the upper hemisphere (all directions above the horizon). A high RDF means the antenna has strong directivity - it receives well in one direction but poorly in others. This is good for rejecting noise and interference from unwanted directions. RDF is particularly important for receiving antennas on noisy bands (like 160/80 meters) where rejecting noise from most directions is more valuable than high peak gain. RDF quantifies this directional advantage.
Exam Tip
RDF = Peak gain / Average gain over hemisphere. Remember: Receiving directivity factor (RDF) is peak antenna gain compared to average gain over the hemisphere around and above the antenna - it measures directional concentration.
Memory Aid
"**R**DF = **P**eak **G**ain / **A**verage **H**emisphere (think 'RDF = PG/AH')"
Real-World Application
You measure your Beverage antenna's RDF. The peak gain (in the forward direction) is, say, 10 dBi. The average gain over the upper hemisphere (all directions) is maybe 0 dBi. The RDF is 10 dB - this means the antenna concentrates reception 10 dB better in the peak direction than the average. High RDF is good for rejecting noise.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. RDF isn't forward gain compared to reverse gain. That would be front-to-back ratio, not RDF.
Option B: Incorrect. RDF isn't relative directivity compared to isotropic. That would be gain in dBi, not RDF.
Option C: Incorrect. RDF isn't relative directivity compared to a dipole. RDF compares peak gain to average gain over the hemisphere.
题目解析
The correct answer is D: Peak antenna gain compared to average gain over the hemisphere around and above the antenna. Receiving directivity factor (RDF) is peak antenna gain compared to average gain over the hemisphere around and above the antenna. It measures how much the antenna concentrates reception in specific directions. RDF compares the peak gain (in the best direction) to the average gain over the upper hemisphere (all directions above the horizon). A high RDF means the antenna has strong directivity - it receives well in one direction but poorly in others. This is good for rejecting noise and interference from unwanted directions. RDF is particularly important for receiving antennas on noisy bands (like 160/80 meters) where rejecting noise from most directions is more valuable than high peak gain. RDF quantifies this directional advantage.
考试技巧
RDF = Peak gain / Average gain over hemisphere. Remember: Receiving directivity factor (RDF) is peak antenna gain compared to average gain over the hemisphere around and above the antenna - it measures directional concentration.
记忆口诀
**R**DF = **P**eak **G**ain / **A**verage **H**emisphere (think 'RDF = PG/AH')
实际应用示例
You measure your Beverage antenna's RDF. The peak gain (in the forward direction) is, say, 10 dBi. The average gain over the upper hemisphere (all directions) is maybe 0 dBi. The RDF is 10 dB - this means the antenna concentrates reception 10 dB better in the peak direction than the average. High RDF is good for rejecting noise.
错误选项分析
Option A: Incorrect. RDF isn't forward gain compared to reverse gain. That would be front-to-back ratio, not RDF. Option B: Incorrect. RDF isn't relative directivity compared to isotropic. That would be gain in dBi, not RDF. Option C: Incorrect. RDF isn't relative directivity compared to a dipole. RDF compares peak gain to average gain over the hemisphere.
知识点
Receiving directivity factor, RDF, Peak gain, Average gain
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.