Deep Dive: E9A02
The correct answer is D: 286 watts. To calculate Effective Radiated Power (ERP), you account for all gains and losses: ERP = Transmitter Power × (Gain - Losses). Convert dB to ratios: gain = 10^(dB/10), loss subtracts from gain. Given: 150W transmitter, 2 dB feedline loss, 2.2 dB duplexer loss, 7 dBd antenna gain. Net gain = 7 dBd - 2 dB - 2.2 dB = 2.8 dB. Converting: 2.8 dB = 10^(2.8/10) = 1.905 ratio. ERP = 150W × 1.905 = 286W. ERP accounts for transmitter power, feedline losses, duplexer losses, and antenna gain to give the effective power radiated by the antenna.
Why Other Answers Are Wrong
Option A: Incorrect. 469 watts would result from not properly accounting for losses or using incorrect dB conversions. Option B: Incorrect. 78.7 watts would result from subtracting gains instead of properly calculating net gain minus losses. Option C: Incorrect. 420 watts would result from incorrect calculation of the net gain/loss combination.
Exam Tip
ERP = Power × (Gain - Losses). Remember: ERP accounts for transmitter power, feedline loss, duplexer loss, and antenna gain. Net gain = antenna gain - feedline loss - duplexer loss. Convert dB to ratio: 10^(dB/10).
Memory Aid
**E**RP = **P**ower × (**G**ain - **L**osses) (think 'ERP = P×(G-L)', 150W, net +2.8dB = 286W)
Real-World Example
Your repeater has 150W transmitter output. After 2 dB feedline loss and 2.2 dB duplexer loss, you have 7 dBd antenna gain. Net gain = 7 - 2 - 2.2 = 2.8 dB = 1.905×. ERP = 150W × 1.905 = 286W. This is the effective power your antenna radiates, accounting for all losses and gains.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E9A
Reference: FCC Part 97.313
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E9A topic.