J-Pole Antenna Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Electrical results can look precise while a unit, operating mode, or component assumption quietly changes the answer. J-Pole Antenna Calculator keeps the calculation tied to the quantities on this page, so you can trace the displayed long section dimension (a) back to the values you entered rather than treating it as a black-box number.

What this calculator does

The J-Pole Antenna Calculator turns Frequency, Velocity factor into the page’s Long section dimension (A) using the circuit or component relationship below. Where the page shows supporting quantities, they come from the same idealized model so you can cross-check the headline rather than reading one isolated number.

How to use it

Start with the fields that actually drive this result: Frequency, Velocity factor. Keep units consistent with the menus beside the fields and avoid mixing values measured under different conditions. After calculating, change one input at a time if you are comparing scenarios; that makes cause-and-effect much easier to see.

How the calculation works

The antenna dimensions start from wavelength λ = v/f, with propagation velocity adjusted by the entered velocity factor. The page then scales that wavelength into the long section, short section, feed point, and spacing estimates used by its J-pole geometry.

Example

Using the page’s default example (Frequency = 146 MHz; Velocity factor = 0.96), the calculator reports Long section dimension (A) of 1.478429 m. Change one driving input at a time and confirm the result moves in the direction predicted by the equation; that is a quick way to catch a unit or mode mistake.

How to interpret the result

Interpret the Long section dimension (A) as an idealized circuit/component quantity for the exact mode and units entered. Use it to compare designs or check hand calculations, but keep component tolerances, ratings, frequency dependence, and real operating conditions in view before turning the number into a hardware decision.

Limitations and notes

The material selector does not currently change the numerical dimensions by itself; the entered velocity factor is what changes propagation length. Real tuning also depends on conductor diameter, surroundings, feed line, matching, and installation height.