Dipole Calculator
Calculate half-wave dipole antenna length and wavelength for any 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 dipole to resonate.
Calculate Length
Click calculate to get the wavelength and half-wave dipole length. The calculator accounts for end effect (typically 5% shorter).
Build Your Dipole
Each arm of the dipole should be half the calculated length. The total dipole spans the full length end to end.
Formula
λ = c / f
L = (λ / 2) × 0.95
Where:
- λ = Wavelength (m)
- c = Speed of light = 299,792,458 m/s ≈ 3 × 108 m/s
- f = Frequency (Hz)
- L = Half-wave dipole length (m)
- 0.95 = End effect correction factor (typically 5% shorter)
Key Points:
- Half-wave dipole length = wavelength / 2
- End effect makes actual length slightly shorter (typically 5%)
- Each arm = L / 2 (total dipole = L)
- Higher frequency = shorter dipole
- Lower frequency = longer dipole
Example 1:
Frequency = 100 MHz
λ = 299,792,458 / (100 × 106) = 2.998 m
L = (2.998 / 2) × 0.95 = 1.499 × 0.95 = 1.423 m
Each arm = 0.712 m
Example 2:
Frequency = 146.52 MHz (2-meter ham band)
λ = 299,792,458 / (146.52 × 106) = 2.046 m
L = (2.046 / 2) × 0.95 = 0.972 m
Each arm = 0.486 m
About Dipole Calculator
The Dipole Calculator is a free online tool that helps you calculate the length of a half-wave dipole antenna for any frequency. A dipole antenna is one of the simplest and most commonly used antenna types, consisting of two conductive elements (arms) of equal length. The half-wave dipole is resonant at its design frequency and provides good radiation efficiency.
When to Use This Calculator
- Antenna Design: Design dipole antennas for specific frequencies
- Ham Radio: Calculate dipole lengths for amateur radio bands
- Radio Communications: Design antennas for radio transmitters and receivers
- Wireless Systems: Calculate antenna dimensions for wireless communication
- Educational Purposes: Learn about antenna theory and wavelength calculations
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 wavelength and dipole length
- ✅ End Effect Correction: Accounts for typical 5% shortening
- ✅ Free Tool: No registration or payment required
- ✅ Educational: Includes formulas and examples for learning
Common Applications
Amateur Radio: Ham radio operators use dipole antennas for various bands. A 20-meter band (14 MHz) dipole is approximately 10 meters long (5 meters per arm), while a 2-meter band (146 MHz) dipole is about 1 meter long (0.5 meters per arm).
FM Radio: FM broadcast antennas often use dipole arrays. At 100 MHz, a dipole is approximately 1.4 meters long, making it practical for many installations.
WiFi Antennas: 2.4 GHz WiFi uses very short dipoles (about 6 cm per arm), while 5 GHz WiFi uses even shorter dipoles (about 3 cm per arm).
Shortwave Radio: Shortwave broadcasters use dipole antennas for various frequencies. Lower frequencies require longer dipoles, while higher frequencies use shorter ones.
Tips for Accurate Results
- Enter frequency in megahertz (MHz) - the calculator converts to hertz internally
- End effect correction (5%) is typical - actual length may vary slightly
- Each arm should be half the calculated length
- Higher frequencies require shorter dipoles
- Consider wire diameter - thicker wire may need slightly different length
- For best results, fine-tune length after construction using an SWR meter
- Keep dipole elements straight and away from metal objects for best performance
Frequently Asked Questions
What is a half-wave dipole?
A half-wave dipole is an antenna where the total length is approximately half the wavelength of the operating frequency. It consists of two equal-length arms, each a quarter-wavelength long. It's the most common dipole configuration and provides good impedance matching (approximately 73 ohms).
What is end effect?
End effect is the phenomenon where the effective electrical length of an antenna is slightly shorter than its physical length due to capacitance at the ends. This typically makes the antenna about 5% shorter than the theoretical half-wavelength. The calculator accounts for this correction.
Can I use this for full-wave dipoles?
This calculator is for half-wave dipoles. For full-wave dipoles, the length would be approximately equal to the wavelength (not half). However, full-wave dipoles are less commonly used than half-wave dipoles.
What's the impedance of a half-wave dipole?
In free space, a half-wave dipole has an impedance of approximately 73 ohms. In practice, this can vary from 50-75 ohms depending on height above ground, nearby objects, and other factors. Most coaxial cables are 50 or 75 ohms, making dipoles relatively easy to match.
How do I feed a dipole antenna?
Dipoles are typically center-fed, meaning the feedline (coaxial cable) connects to the center point between the two arms. This provides balanced feed and good impedance matching. A balun (balanced-to-unbalanced transformer) may be used when connecting to coaxial cable.