J-Pole Antenna Calculator
Calculate J-pole antenna dimensions for your operating frequency
Megahertz (MHz)
How to Use This Calculator
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
Frequently Asked 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.