RCDD · Question #325
If the input signal power to a communication system is 1 W and the output power is 1 mW, the system attenuation is:
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
How the community answered
(54 responses)- A9% (5)
- B2% (1)
- C83% (45)
- D2% (1)
- E4% (2)
Why each option
This question tests the ability to calculate signal power attenuation expressed in decibels given input and output power values.
3 dB represents a power ratio of approximately 2:1, far less than the 1000:1 ratio between 1 W and 1 mW.
20 dB corresponds to a 100:1 power ratio, which would require an output of 10 mW rather than 1 mW.
Attenuation in dB is calculated using the formula 10 * log10(Pin/Pout). With 1 W (1000 mW) input and 1 mW output, the ratio is 1000:1, yielding 10 * log10(1000) = 10 * 3 = 30 dB. This standard power-ratio formula is fundamental to all telecommunications link budget and signal-loss analysis.
40 dB corresponds to a 10,000:1 power ratio, which would require an output of 0.1 mW rather than 1 mW.
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
Source: https://www.itu.int/rec/T-REC-G.100/en
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