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SESK: Stuff Everyone Should Know · sesk.info/hame-velocity-factor-dielectric

Which factor has the biggest effect on the velocity factor of a transmission line?

The insulating dielectric material.

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  1. The characteristic impedance
  2. The transmission line length
  3. The insulating dielectric material ✔

Why: Waves slow down in the plastic or foam between the conductors. Solid polyethylene gives a lower velocity factor than foam or air.

Huh, didn't know that: Foam dielectric coax has lower loss per unit length than solid dielectric coax of the same size (E9F08).

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What do you say when your rigid coax order is late and the company refuses to renegotiate? We are taking a hard-line stance.
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References

Answer: The insulating dielectric material. Waves slow down in the plastic or foam between the conductors. Solid polyethylene gives a lower velocity factor than foam or air.

  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
    C. The insulating dielectric material
    Checked 2026-10-11.

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