J-Pole Antenna Calculator
Calculate J-pole antenna dimensions for your operating frequency
Megahertz (MHz)
Instructions
Enter Frequency
Enter the operating frequency in megahertz (MHz). This is the frequency at which you want the J-pole to operate.
Calculate Dimensions
Click calculate to get the quarter-wave and three-quarter-wave section lengths. The calculator accounts for end effect.
Build Your J-Pole
The J-pole consists of a quarter-wave short stub and a three-quarter-wave main element. Total length is approximately one full wavelength.
Formula
λ = c / f
Lquarter = (λ / 4) × 0.95
L3/4 = (3λ / 4) × 0.95
Where:
- λ = Wavelength (m)
- c = Speed of light = 299,792,458 m/s
- f = Frequency (Hz)
- Lquarter = Quarter-wave section length (m)
- L3/4 = Three-quarter-wave section length (m)
- 0.95 = End effect correction factor
Example:
Frequency = 146.52 MHz (2-meter ham band)
λ = 299,792,458 / (146.52 × 106) = 2.046 m
Lquarter = (2.046 / 4) × 0.95 = 0.486 m
L3/4 = (3 × 2.046 / 4) × 0.95 = 1.458 m
About J-Pole Antenna Calculator
The J-Pole Antenna Calculator helps you design J-pole antennas for any frequency. A J-pole antenna is a vertical antenna consisting of a quarter-wave short stub and a three-quarter-wave main radiating element. It's popular among amateur radio operators because it's simple to build, requires no ground plane, and provides good performance.
When to Use This Calculator
- Amateur Radio: Design J-pole antennas for ham radio bands
- VHF/UHF Communications: Calculate dimensions for VHF/UHF frequencies
- Antenna Building: Build your own J-pole antenna
- Educational Purposes: Learn about J-pole antenna design
Why Use Our Calculator?
- Accurate Calculations: Uses speed of light and accounts for end effect
- Easy to Use: Simple interface requiring only frequency
- Dual Output: Shows both quarter-wave and three-quarter-wave sections
- Free Tool: No registration required
- Educational: Includes formulas and examples
Common Applications
2-Meter Ham Band: J-pole antennas are popular for the 2-meter (144-148 MHz) amateur radio band. They're easy to build from copper pipe or aluminum and provide good performance without a ground plane.
70cm Band: J-poles work well for the 70cm (420-450 MHz) band, providing compact vertical antennas for UHF communications.
Tips for Accurate Results
- Enter frequency in megahertz (MHz)
- End effect correction (5%) is typical
- Quarter-wave section is the short stub
- Three-quarter-wave section is the main radiating element
- Fine-tune length after construction using an SWR meter
- Keep antenna vertical for best performance
Common Questions
What is a J-pole antenna?
A J-pole is a vertical antenna consisting of a quarter-wave short stub and a three-quarter-wave main element, forming a J shape. It's an end-fed antenna that doesn't require a ground plane, making it popular for portable and rooftop installations.
Why is it called a J-pole?
The antenna forms a J shape when viewed from the side - the short stub extends horizontally, and the main element extends vertically, creating a J-like appearance.
Does it need a ground plane?
No, J-pole antennas don't require a ground plane, unlike quarter-wave vertical antennas. This makes them easier to install and more portable.
What's the typical impedance?
J-pole antennas typically have an impedance around 50 ohms at the feed point, making them compatible with standard 50-ohm coaxial cable without needing a matching network.