Dipole Antenna Calculator
Calculate the optimal wire length for your dipole antenna. Supports horizontal dipoles and inverted vee configurations across all amateur radio bands.
What is a Dipole Antenna?
The dipole antenna is one of the most popular and effective antennas in amateur radio. It consists of two equal-length wire elements fed at the center, creating a simple yet highly efficient radiator. The classic “half-wave dipole” is approximately half a wavelength long at the operating frequency.
Horizontal Dipole
The traditional configuration where the antenna is strung horizontally between two supports. Provides excellent DX (long-distance) performance with low-angle radiation. Best results are achieved when installed at least 1/2 wavelength above ground.
Inverted Vee
A popular variant where the feedpoint is at the top of a single support and the wires slope downward. Easier to install than a horizontal dipole and requires less space. The inverted vee provides good omnidirectional coverage, making it ideal for general operating and contesting.
Key Advantages
- Simple construction with minimal materials (wire, insulators, feedline)
- Efficient radiation with good gain (2.15 dBi in free space)
- Self-resonant design requiring no tuner on the design frequency
- Relatively quiet reception compared to vertical antennas
- Versatile - works well for both DX and local communications
- Low cost and easy to repair or modify
Dipole Antenna Length Formula
The classic dipole antenna formula (also known as the 468 formula) calculates the approximate length:
Length (feet) = 468 / Frequency (MHz)Length (meters) = 143 / Frequency (MHz)Each side = Total Length / 2However, the 468 formula is a simplified approximation. Our antenna length calculator applies end-effect corrections based on wire diameter, configuration adjustments for inverted vees (typically 2-5% shorter), and height considerations for more accurate results. For precise tuning, always start 2-3% longer than calculated.
Tuning Your Dipole Antenna
Even with precise calculations, every dipole needs fine-tuning after installation. Here is the recommended process:
- Start Long: Cut the wire 2-3% longer than the calculated length. It is much easier to trim wire than to add length.
- Initial Installation: Install the antenna at the planned height with proper insulators and feedline. Ensure the antenna is as straight and level as possible.
- Measure SWR: Using an antenna analyzer or SWR meter, measure the SWR across your intended operating frequency range. Note the frequency of minimum SWR.
- Adjust Length: If the minimum SWR is below your desired frequency, the antenna is too long - shorten it. If the minimum is above your frequency, the antenna is too short (you will need to lower the operating frequency or use a tuner).
- Trim Carefully: Remove small amounts (5-10cm or 2-4 inches) from each end of the antenna, maintaining symmetry. Shortening the antenna raises the resonant frequency.
- Re-measure and Repeat: After each trim, re-measure the SWR. Continue trimming in small increments until the SWR is 1.5:1 or better at your desired frequency.
- Document Settings: Once tuned, record the final length, height, and SWR measurements for future reference.
Pro Tips:
- Use a 1:1 current balun at the feedpoint to reduce common-mode currents
- Seal all connections and insulators to prevent water ingress
- Allow the antenna to “settle” for a day before final tuning ( wire stretches slightly)
- Keep the feedline away from the antenna elements to avoid coupling
- Tune during dry weather for most consistent results
Related Resources
References:
- 66pacific Dipole Calculator
- M0UKD Dipole Calculator
- ARRL Antenna Book (Chapter on Wire Antennas)
- FCC Part 97 - Amateur Radio Service Regulations (antenna height limits)