Subelement J: Antennas— Topic 67: Effective Radiated Power
Question 3-67J2
Element 3 (GROL)What is the effective radiated power of a repeater with 75 watts transmitter power output, 4 dB feedline loss, 3 dB duplexer and circulator loss, and 10 dB antenna gain?
Explanation
Effective Radiated Power (ERP) is the power a transmitting antenna effectively radiates after accounting for all gains and losses in the system. To calculate ERP, combine the system losses and antenna gain in dB, then apply this net effect to the transmitter power output.
First, sum the losses in dB:
Feedline loss = 4 dB
Duplexer and circulator loss = 3 dB
Total system loss = 4 dB + 3 dB = 7 dB
Next, calculate the net gain in dB:
Antenna gain = 10 dB
Net gain = Antenna Gain - Total System Loss = 10 dB - 7 dB = 3 dB
A 3 dB gain represents a doubling of power. Therefore, multiply the transmitter power output by 2:
ERP = Transmitter Power Output * $10^{(Net Gain dB / 10)}$
ERP = 75 watts * $10^{(3 / 10)}$
ERP = 75 watts * 2
ERP = 150 watts.
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