EMC Question of the Week: December 3, 2018
What effect does increasing the resolution bandwidth of a spectrum analyzer from 9 kHz to 120 kHz generally have on the noise floor?
- no significant effect
- increases it by 11 dB
- increases it by 22 dB
- decreases it by 22 dB
Answer
The correct answer is "b". Increasing the resolution bandwidth from 9 kHz to 120 kHz captures broadband noise in a frequency range that is 13.3 times greater. That's an increase in the noise power of 10 log(13.3) or approximately 11 dB. This will be true no matter what the source of the broadband noise is. On the other hand, changing the resolution bandwidth has no significant effect on the measured amplitude of narrowband signals or noise.
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