EMC Question of the Week: September 9, 2019

A 30-dB attenuator reduces the signal voltage by approximately a factor of

1. 3
2. 3.3
3. 30
4. 1000

Answer

The correct answer is "c". Converting from decibels to a voltage ratio, 

${10}^{30/20}=31.6$

or working it in the other direction, 20 log(31.6) = 30 dB. Note that 10 dB is approximately a factor of 3. Even without a calculator, we can readily calculate that 30 dB is 20 dB + 10 dB or a voltage ratio of 10 x 3 = 30.

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