This tool calculates the length of an antenna that is 5/8 wavelengths (λ) in size.
Calculator
Enter the frequency and the tool will calculate the length
Formula
L = (5/8)*(c/f)
where
- c is the speed of light ≈ 3*108 m/s
- f is the frequency in MHz
L is the length of the 5/8 λ antenna
Example Calculation
Let’s calculate the length of a 5/8 wave antenna for 27 MHz, which is a common frequency used for CB radio communications.
Using the calculator, the length is found to be 6.94 meters.
Background
What Is a 5/8 Wave Antenna?
A 5/8 wave antenna is an antenna whose physical length is 5/8 of the wavelength of the frequency it is designed to operate at. The term “5/8 wave” refers to the fact that the antenna is slightly longer than a half-wave antenna, and it is specifically tuned to optimize performance for certain applications. Its design provides a high level of gain and a low takeoff angle of radiation, which improves communication range, especially for long-distance ground communications.
Key Characteristics of a 5/8 Wave Antenna
- Length: The length of the antenna is 5/8 of the wavelength of the frequency it is designed for.
- Radiation Pattern: It has a low-angle radiation pattern, which helps focus the signal along the ground, making it ideal for mobile and long-distance communication.
- Impedance Matching: Often requires a matching network to match the impedance with the transmission line, as the natural impedance of a 5/8 wave antenna is not always a perfect match for the typical 50-ohm coaxial cables used in most communication systems.
How Does a 5/8 Wave Antenna Work?
The 5/8 wave antenna works by utilizing its length and design to produce a lower angle of radiation, which is particularly useful for communicating over long distances, especially in line-of-sight or near-line-of-sight communication. In comparison to a quarter-wave antenna, which radiates in more of a doughnut-shaped pattern, a 5/8 wave antenna compresses the signal closer to the ground, maximizing its reach.
Benefits of the 5/8 Wave Design
- Low Takeoff Angle: The low-angle radiation pattern means the signal travels closer to the ground, reducing skyward loss and improving ground-level communication.
- Increased Gain: The 5/8 wave antenna offers higher gain than a typical quarter-wave antenna, making it more effective for mobile communications where extending range is important.
- Directional Efficiency: It focuses more of the signal power in the horizontal plane, which is beneficial when the goal is to reach distant stations on the horizon rather than upward to the sky.