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SESK: Stuff Everyone Should Know · sesk.info/hame-dbi-to-dbd

An antenna has 6 dB gain over an isotropic radiator. What is its gain over a half-wave dipole?

3.85 dB over a dipole.

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  1. 6.0 dB
  2. 3.85 dB ✔
  3. 8.15 dB

Why: A half-wave dipole already has 2.15 dB gain over isotropic. Subtract that from 6 dBi and you get 3.85 dBd.

Huh, didn't know that: Antenna efficiency is radiation resistance divided by total resistance (E9A09).

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References

Answer: 3.85 dB. A half-wave dipole already has 2.15 dB gain over isotropic. Subtract that from 6 dBi and you get 3.85 dBd.

  1. NCVEC 2024-2028 Amateur Extra Question Pool, 4th Errata (Feb 4, 2026) ncvec.org/downloads/2024-2028%20Extra%20Class%20Question%20Pool%20and%20Syllabus%20Public%20Release%20with%204th%20Errata%20Feb%204%202026.pdf
    A. 3.85 dB
    Checked 2026-10-11.

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