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What is the frequency above which a low-pass filter's output power is less than half the input power?

The cutoff frequency.

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  1. Notch frequency
  2. Cutoff frequency ✔
  3. Neper frequency

Why: A low-pass filter passes low frequencies. The cutoff frequency is where its output power has fallen to half the input power. A notch filter blocks a narrow band, and neper is a unit, not a filter frequency.

Huh, didn't know that: A band-pass filter's bandwidth is measured between its upper and lower half-power frequencies.

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References

Answer: Cutoff frequency. A low-pass filter passes low frequencies. The cutoff frequency is where its output power has fallen to half the input power. A notch filter blocks a narrow band, and neper is a unit, not a filter frequency.

  1. NCVEC 2023-2027 General Class Pool and Syllabus (6th Errata, Feb 4 2026) ncvec.org/downloads/General%20Class%20Pool%20and%20Syllabus%202023-2027%20Public%20Release%20with%206th%20Errata%20Feb%204%202026.pdf
    Cutoff frequency
    Checked 2026-10-11.

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