Deep Dive: G9C04
The correct answer is B: Gain in dBi is 2.15 dB higher. How antenna gain in dBi compares to gain stated in dBd for the same antenna is that gain in dBi is 2.15 dB higher. dBi is relative to isotropic (theoretical), dBd is relative to dipole. A dipole has 2.15 dBi gain, so dBi = dBd + 2.15. For amateur radio operators, this is important when comparing gain specifications. Understanding this helps when evaluating antennas.
Why Other Answers Are Wrong
Option A: Incorrect. dBi isn't 2.15 dB lower - it's 2.15 dB higher because dBi is relative to isotropic, dBd is relative to dipole. Lower is wrong. Option C: Incorrect. dBd isn't 1.25 dBd lower - the difference is 2.15 dB, and dBd is lower than dBi. 1.25 dBd is wrong. Option D: Incorrect. dBd isn't 1.25 dBd higher - dBd is lower than dBi by 2.15 dB. Higher is wrong.
Exam Tip
dBi vs dBd = dBi is 2.15 dB higher. Think 'd'Bi = 'd'Bd + '2'.15. dBi is relative to isotropic, dBd is relative to dipole. A dipole has 2.15 dBi gain, so dBi = dBd + 2.15. Not lower, not 1.25 dBd - just 2.15 dB higher.
Memory Aid
dBi vs dBd = dBi is 2.15 dB higher. Think 'd'Bi = 'd'Bd + '2'.15. dBi is relative to isotropic, dBd is relative to dipole. dBi = dBd + 2.15. Important conversion factor.
Real-World Example
An antenna has 10 dBd gain. In dBi, that's 10 + 2.15 = 12.15 dBi. dBi is relative to isotropic (theoretical point source), dBd is relative to a dipole. Since a dipole has 2.15 dBi gain, dBi is always 2.15 dB higher than dBd for the same antenna. This is the conversion factor.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G9C
Reference: 2023-2027 Question Pool · G9 - Antennas and Feed Lines
Key Concepts
Verified Content
Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G9C topic.