Quarter Wave Vertical Antenna Calculator
Enter the operating frequency in MHz to size a quarter-wave vertical or ground-plane radiator. The tool returns the element length in feet, metres and inches.
How to use the quarter wave vertical calculator
- Enter your operating frequency in megahertz, for example 146 for the 2 metre band.
- Read the radiator length in feet, metres and inches.
- Cut the element a little long, then trim while checking SWR for the lowest dip.
Examples
20 metre vertical at 14.2 MHz
frequencyMhz = 14.2
length = 16.48 ft (5.02 m, 197.75 in)
2 metre vertical at 146 MHz
frequencyMhz = 146
length = 1.60 ft (19.23 in)
Frequently asked questions
What is the quarter-wave vertical formula?
The radiator length of a quarter-wave vertical in feet is 234 divided by the frequency in MHz. Multiply feet by 0.3048 for metres or by 12 for inches.
Why is a quarter-wave the same length as one dipole leg?
A quarter-wave vertical is electrically one half of a dipole, with the ground or radials acting as the missing half. So its length matches a single dipole leg, which is also 234 divided by the frequency.
Do I need radials for a ground-plane antenna?
Yes. A vertical works against a ground plane, so it needs radials or an earth connection to act as the return. Four or more quarter-wave radials are common for a ground-plane build.
Should I cut the element exactly to the calculated length?
Cut it slightly long and trim. Mounting height, radial angle and the element diameter all shift resonance, so trimming to the lowest SWR beats cutting exactly and ending up short.
Does this calculator work for VHF and UHF?
Yes. The 234 formula holds across HF, VHF and UHF. Enter the frequency in MHz, such as 146 for 2 metres or 446 for 70 centimetres.
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