J-Pole Antenna Calculator

Instructions

This calculator determines the approximate dimensions of a J-Pole antenna. A J-Pole is a variation of a half-wavelength dipole, known for its end-fed design.

Input: Enter the desired operating frequency in Megahertz (MHz). For example, for the 2-meter amateur radio band, you would enter 144 (MHz).

Calculation: Click the "Calculate" button. The calculator will determine the required lengths of the radiating element and the matching section (the "J" part) based on the chosen units (imperial or metric).

Units: Use the buttons to toggle between imperial (feet and inches) and metric (meters and centimeters) units for the results.

Formula (Approximation):

Metric:
Radiating Element (meters) = 142.5 / Frequency (MHz)
Matching Section (meters) = Radiating Element / 2

Imperial:
Radiating Element (feet) = 468 / Frequency (MHz)
Matching Section (feet) = Radiating Element / 2

Important Considerations:

• These calculations provide a starting point. The actual resonant frequency can be affected by factors such as the height above ground, the diameter of the wire used, and nearby objects.
• The impedance matching of a J-Pole can be influenced by the spacing between the matching section wires. This calculator does not calculate that spacing. Experimentation might be needed.
• For precise tuning, it is recommended to use an antenna analyzer to measure the Standing Wave Ratio (SWR) and make adjustments to the antenna dimensions as needed.
• Always observe safe practices when working with antennas, especially regarding power levels and heights.