RCDD Question #325: Real Exam Question with Answer & Explanation

The correct answer is C. 30 dB. This question tests the ability to calculate signal power attenuation expressed in decibels given input and output power values.

Question

If the input signal power to a communication system is 1 W and the output power is 1 mW, the system attenuation is:

Options

A3 dB
B20 dB
C30 dB
D40 dB
E1000 dB

Explanation

This question tests the ability to calculate signal power attenuation expressed in decibels given input and output power values.

Common mistakes.

A. 3 dB represents a power ratio of approximately 2:1, far less than the 1000:1 ratio between 1 W and 1 mW.
B. 20 dB corresponds to a 100:1 power ratio, which would require an output of 10 mW rather than 1 mW.
D. 40 dB corresponds to a 10,000:1 power ratio, which would require an output of 0.1 mW rather than 1 mW.
E. 1000 dB is not a meaningful attenuation value and does not correspond to any realistic communication system loss.

Concept tested. Decibel power attenuation formula calculation

Reference. https://www.itu.int/rec/T-REC-G.100/en

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