E9A07

ANTENNAS AND TRANSMISSION LINES · Basic antenna parameters: radiation resistance, gain, beamwidth, efficiency; effective radiated power (ERP) and effective isotropic radiated power (EIRP)

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What is the effective isotropic radiated power (EIRP) of a repeater station with 200 watts transmitter power output, 2 dB feed line loss, 2.8 dB duplexer loss, 1.2 dB circulator loss, and 7 dBi antenna gain?

A159 watts
B252 watts
C632 watts
D63.2 watts

Why Work the whole chain in decibels, then convert once. Losses total 2 + 2.8 + 1.2 = 6 dB, and the antenna adds 7 dBi, so the net gain is +1 dB. A gain of 1 dB is a power ratio of about 1.26, so 200 W x 1.26 = 252 W. Because the antenna gain is given in dBi (referenced to an isotropic radiator), the result is EIRP directly, with no 2.15 dB correction needed.

Watch out The choice near 159 watts is what you get if you treat the net as -1 dB, that is, if you subtract the gain and add the losses backwards; watch the sign of each term.

Add gains, subtract losses in dB first, convert last. dBi in means EIRP out; dBd in means ERP out.

HamSandwich explanation, first draft. The question and answers are the NCVEC text.

E9A07

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