Question
What is the effective radiated power (ERP) of a repeater station with 150 watts transmitter power output, 2 dB feed line loss, 2.2 dB duplexer loss, and 7 dBd antenna gain?
Answer Options
- A) 469 watts
- B) 78.7 watts
- C) 420 watts
- D) 286 watts
Correct Answer: D
Explanation
Effective Radiated Power (ERP) is the power actually radiated from the antenna in the direction of its maximum gain, relative to a half-wave dipole. It is calculated by starting with the transmitter power and applying all gains (antenna gain) and losses (feed line and filtering losses) in the system. The antenna gain is given in dBd (decibels relative to a dipole), so the result is ERP in Watts.
First, convert the transmitter power to dBm (if necessary, 150 W \approx 51.76 dBm) or work directly in Watts/dB. Using dB math: Gain dB = Antenna Gain - Feed line Loss - Duplexer Loss = 7 dB - 2 dB - 2.2 dB = +2.8 dB. The ERP is 150 W \times 10^{(2.8/10)} \approx 150 W \times 1.905 \approx 285.8 W. Therefore, the ERP is approximately 286 watts.
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