J-Pole Antenna Calculator
Calculate J-Pole antenna dimensions for any frequency band. Get long section, short section, feed point, and spacing in cm with charts and formula breakdowns. Free online antenna design tool for ham radio.
About This Calculator
The J-Pole Antenna Calculator helps amateur radio operators, RF engineers, and antenna enthusiasts design a J-pole antenna for any frequency band. Simply enter your desired operating frequency in MHz and select the antenna material or velocity factor to instantly compute all four critical dimensions: long section (A), short section (B), feed point (C), and spacing (D).
The J-pole antenna (also known as the J antenna) is a popular vertical omnidirectional antenna widely used in amateur radio, maritime communications, and shortwave broadcasting. Its design resembles the letter J, with a half-wave radiator fed by a quarter-wave matching section. The calculator uses the formula wavelength = speed of light / frequency to determine the wavelength, then applies velocity factor corrections based on your chosen material. The long section A = 0.75λ × VF, short section B = (λ/4) × VF, feed point C = (λ/50) × VF, and spacing D = 0.045λ / 2.
Regional Notes
India (IN): The Wireless Planning and Coordination (WPC) wing regulates amateur radio frequencies. J-pole antennas are commonly used on the 2-meter (144-146 MHz) and 70-centimeter (430-440 MHz) bands. Amateur radio operators require a valid license from the WPC.
United States (US): The FCC regulates amateur radio under Part 97. Popular J-pole bands include 2-meter (144-148 MHz), 70-centimeter (420-450 MHz), and 6-meter (50-54 MHz). The National Association for Amateur Radio (ARRL) provides extensive J-pole building resources.
United Kingdom (UK): Ofcom regulates amateur radio under the Wireless Telegraphy Act. Common bands include 2-meter (144-146 MHz) and 70-centimeter (430-440 MHz). The Radio Society of Great Britain (RSGB) offers guidance on antenna construction.
Frequently Asked Questions
What is a J-pole antenna?
A J-pole antenna (also known as J antenna) is a vertical omnidirectional antenna whose shape resembles the letter J. It was invented in 1909 by Hans Beggerow for use in Zeppelin airships. J-pole antennas are widely used in shortwave frequency bands for amateur radio, maritime communications, and international shortwave broadcasting.
How does the J-pole antenna calculator work?
Enter your desired frequency in MHz and select the antenna material or velocity factor. The calculator uses the formula wavelength = c/f and computes four key dimensions: Long section (A = 0.75×λ×VF), short section (B = λ/4×VF), feed point (C = λ/50×VF), and spacing (D = 0.045×λ/2). Results are displayed in centimeters with charts.
What is the velocity factor of a copper J-pole antenna?
Bare copper wire has a velocity factor of approximately 0.96, meaning the signal travels at 96% of the speed of light. The calculator includes presets for common materials including copper, aluminium, balanced feeders, optical fibers, and various dielectrics.
Are J-pole antennas directional?
No, J-pole antennas are not directional. They are omnidirectional antennas where radio power radiates equally in all directions perpendicular to the azimuth axis. The radiation pattern resembles a doughnut shape in three dimensions.
What frequency bands can I use with this calculator?
This calculator works for any frequency band. Simply enter your desired frequency in MHz. Common bands include 2-meter (144-148 MHz), 70-centimeter (430-440 MHz), and HF bands (1.8-30 MHz). The calculator automatically adjusts all four dimensions based on the wavelength.
How do I mount a J-pole antenna?
Use antenna mounting accessories to put the antenna on a chimney or roof. Keep your antenna at least six feet from metal objects. Use a choke balun to prevent RF energy from traveling back down the feed line. Create a drip loop to relieve connector stress. Seal connections with electrical tape. Do not use a ground plane for a J-pole.
Is the J-pole antenna calculator free?
Yes, it is completely free to use with no registration required. You can share your calculation results via URL.