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SESK: Stuff Everyone Should Know · sesk.info/hame-pin-diode-rf-switch

What characteristic of a PIN diode makes it useful as an RF switch?

Low junction capacitance lets a PIN diode switch RF cleanly.

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  1. Extremely high reverse breakdown voltage
  2. Ability to dissipate large amounts of power
  3. Low junction capacitance ✔

Why: When reverse biased, a PIN diode has so little capacitance that RF barely passes. Forward bias lets RF pass, so it works as an RF switch.

Huh, didn't know that: Forward DC bias current controls how much a PIN diode attenuates RF (E6B11).

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What do you say when a broken PIN diode switch takes down the RF amplifier? No PIN, no gain.
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References

Answer: Low junction capacitance. When reverse biased, a PIN diode has so little capacitance that RF barely passes. Forward bias lets RF pass, so it works as an RF switch.

  1. NCVEC 2024-2028 Amateur Extra Question Pool, E6B05 (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
    D. Low junction capacitance
    Checked 2026-10-11.
  2. NCVEC 2024-2028 Amateur Extra Question Pool, E6B11 (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. Forward DC bias current
    Checked 2026-10-11.

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