SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/hamg-notch-filter

What does the notch filter on many HF transceivers do?

It reduces interference from carriers in the receiver passband.

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  1. It reduces interference from carriers in the receiver passband ✔
  2. It restricts transmitter voice bandwidth
  3. It removes splatter from adjacent signals

Why: A notch filter cuts out a very narrow slice of the receive passband, such as a steady whistle from a carrier. The rest of the signal comes through.

Huh, didn't know that: Using the opposite sideband when receiving CW can also reduce interference.

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You know you're a ham when you start getting all kinds of RFI complaints from your neighbors.
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References

Answer: It reduces interference from carriers in the receiver passband. A notch filter cuts out a very narrow slice of the receive passband, such as a steady whistle from a carrier. The rest of the signal comes through.

  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
    To reduce interference from carriers in the receiver passband
    Checked 2026-10-10.

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