Deep Dive: E9A07
The correct answer is B: 252 watts. To calculate Effective Isotropic Radiated Power (EIRP), account for all gains and losses: EIRP = Transmitter Power × (Gain - Losses). Convert dB to ratios. Note: EIRP uses dBi (gain relative to isotropic), while ERP uses dBd (gain relative to dipole). Given: 200W transmitter, 2 dB feedline loss, 2.8 dB duplexer loss, 1.2 dB circulator loss, 7 dBi antenna gain. Total losses = 2 + 2.8 + 1.2 = 6 dB. Net gain = 7 dBi - 6 dB = 1 dB. Converting: 1 dB = 10^(1/10) = 1.259 ratio. EIRP = 200W × 1.259 = 252W. EIRP is similar to ERP but uses dBi (isotropic reference) instead of dBd (dipole reference).
Why Other Answers Are Wrong
Option A: Incorrect. 159 watts would result from incorrect calculation of the net gain/loss combination. Option C: Incorrect. 632 watts would result from not properly accounting for losses or using incorrect dB conversions. Option D: Incorrect. 63.2 watts would result from subtracting gains instead of properly calculating net gain minus losses.
Exam Tip
EIRP calculation = Account for all losses and gains in dBi. Remember: EIRP = Power × (Gain in dBi - All Losses). With 200W, 7 dBi gain, and 6 dB losses, net = 1 dB = 1.259×, EIRP = 252W.
Memory Aid
**E**IRP = **2**00W × (**7** dBi - **6** dB) = **2**52W (think 'EIRP = 200×(7-6) = 252W')
Real-World Example
Your station has 200W transmitter, 2 dB feedline loss, 2.8 dB duplexer loss, 1.2 dB circulator loss, and 7 dBi antenna gain. Total losses = 6 dB. Net gain = 7 - 6 = 1 dB = 1.259×. EIRP = 200W × 1.259 = 252W. EIRP uses dBi (isotropic reference), while ERP uses dBd (dipole reference).
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.