How does antenna gain in dBi compare to gain stated in dBd for the same antenna?
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.
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 Application
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.
Key Concepts
Why Other Options 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.
题目解析
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.
考试技巧
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.
记忆口诀
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.
实际应用示例
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.
错误选项分析
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.
知识点
Antenna gain, dBi, dBd, 2.15 dB difference
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.