Deep Dive: E9H03
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.
Why Other Answers 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.
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 Example
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.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E9H
Reference: FCC Part 97.3
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E9H topic.