J-pole antenna calculator

About

This calculator works out the dimensions of a J-pole antenna. The J-pole is a popular vertical for the VHF and UHF bands.

A — overall length, B — stub, C — spacing between the conductors, D — where the feeder attaches

Standard frequencies Enter a frequency by hand144 MHz (2 m)440 MHz (70 cm)LPDPMRGMRSFRS Operating frequency MHz Wire diameter mm Units Millimetres (mm)Centimetres (cm)Metres (m) Result Wavelength (λ) см Dimension A см Dimension B см Spacing C см Dimension D см Velocity factor -

Notes:

• Standard frequencies: pick one from the list of common frequencies, or type your own.
• Units: results can be shown in millimetres, centimetres or metres.
• Dimension A — the length of the upper radiating element (3/4 λ).
• Dimension B — the length of the lower element (1/4 λ).
• Distance C — from the feed point down to the bottom end.
• Dimension D — an extra dimension for tuning.
• The shortening factor is worked out automatically from the frequency and the conductor diameter.
• Conductor diameter affects both the shortening factor and the overall dimensions.
• For best results use a conductor 2–6 mm across.
• The antenna can be built from wire, tubing or metal strip.

© 2026 UR3PKI · CyberDev.Space · Content licensed under CC BY-NC-SA 4.0.

How to cite this calculator

UR3PKI. «J-pole antenna calculator». CyberDev.Space. https://cyberdev.space/en/radio/calculators/antennas/jpole (licence CC BY-NC-SA 4.0).

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