What is the effective radiated power of a repeater with 75 watts transmitter power output, 5 dB feedline loss, 4 dB duplexer and circulator loss, and 6 dB antenna gain?
• Relationship between transmitter power output (TPO) and effective radiated power (ERP) • How to convert dB gains and losses into a power ratio using 10^(dB/10) • How to combine multiple dB values (add gains, subtract losses) before converting back to watts
• First, combine all the dB values into a single net dB change. Are you ending up with a net gain or a net loss overall? • Once you have the net dB change, how do you convert that dB value into a multiplication factor for the original 75 watts? • After finding the multiplication factor from the net dB, what operation do you perform with the original 75 watts to get ERP, and which answer choice is closest to that result?
• Be sure you add all dB gains and losses with sign, e.g., losses as negative dB, gains as positive dB, before converting to a ratio. • Verify that you used 10^(dB/10) (not 20) because you are dealing with power, not voltage. • After computing ERP, double-check whether the result is larger or smaller than 75 watts and confirm that makes sense given the net dB.
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