Practical Antenna Planning
A four element Yagi gives useful forward gain without a long boom. It has one reflector, one driven element, and two directors. This calculator turns frequency into wavelength first. Then it scales each element by proven design ratios. The result is a practical starting point for field building.
Element Length Choices
The reflector is usually the longest element. It sits behind the driven element. The driven element is shorter than a half wave dipole because end effects matter. Each director is slightly shorter again. That taper helps current phase and improves forward radiation. Material diameter, clamps, and a conductive boom can change the final trim. Use the correction fields when your build style needs compensation.
Spacing and Boom Layout
Spacing controls gain, pattern, and feed impedance. Wider spacing may raise gain, but it can reduce front to back performance. Tight spacing can improve rejection, yet it may lower impedance. A balanced design is easier to match. This tool shows each position from the reflector. That makes drilling and boom marking simpler.
Matching and Losses
A small Yagi often has a feed impedance below 50 ohms. A gamma match, hairpin match, or quarter wave transformer may be needed. The calculator estimates the resistive match ratio. It also gives a transformer impedance target. Efficiency affects the estimated gain. Losses can come from coax, joints, corrosion, and poor connections.
Using Results Wisely
These numbers are not a final electromagnetic model. They are a design baseline. After cutting, test the antenna with an analyzer. Trim the driven element first. Move matching parts slowly. Keep notes after each change. Nearby metal, mast size, and mounting height can alter readings. For best accuracy, combine this calculator with outdoor testing and simulation software.
Build Checklist
Start with straight tubing and accurate marks. Keep every element square to the boom. Measure from the same reference edge each time. Use stainless hardware where possible. Seal joints against water. Mount the coax so it leaves the driven element at a right angle. Recheck dimensions before soldering. Save the exported file with your analyzer notes. A repeatable record helps when weather, height, or band conditions make tests confusing. It also speeds later repairs and future band retuning work.