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What are the principal frequencies at the output of a mixer?

The two inputs, their sum and their difference.

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  1. The two inputs plus their sum and difference ✔
  2. Two and four times the input frequency
  3. The square root of the product of the inputs

Why: A mixer multiplies two signals, which creates sum and difference frequencies. The original inputs also leak through. Filters pick the one you want.

Huh, didn't know that: Mixer input levels that are too high generate spurious mixer products (E7E09).

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References

Answer: The two inputs plus their sum and difference. A mixer multiplies two signals, which creates sum and difference frequencies. The original inputs also leak through. Filters pick the one you want.

  1. NCVEC 2024-2028 Amateur Extra Question Pool, E7E08 (4th errata, Feb. 4, 2026) www.ncvec.org/downloads/2024-2028%20Extra%20Class%20Question%20Pool%20and%20Syllabus%20Public%20Release%20with%204th%20Errata%20Feb%204%202026.pdf
    C. The two input frequencies along with their sum and difference frequencies
    Checked 2026-10-11.
  2. NCVEC 2024-2028 Amateur Extra Question Pool, E7E09 (4th errata, Feb. 4, 2026) www.ncvec.org/downloads/2024-2028%20Extra%20Class%20Question%20Pool%20and%20Syllabus%20Public%20Release%20with%204th%20Errata%20Feb%204%202026.pdf
    A. Spurious mixer products are generated
    Checked 2026-10-11.

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