Balun Calculator
Calculate balun impedance ratio, turns ratio and common balun type.
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Inputs
Live
Math
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Related
Enter parameters and click Calculate to view results
Formula & Theory
Impedance Ratio = Zout / Zin, Turns Ratio = √(Zout / Zin)This formula is used to calculate antenna parameters for balun calculator.
Overview
The Balun Calculator determines the impedance transformation ratio, physical winding turns ratio, and suggested configuration for RF baluns (BALanced-to-UNbalanced transformers). It helps ham radio operators, RF circuit designers, and antenna engineers properly interface unbalanced coaxial transmission lines (e.g., 50 Ω coax) to balanced antenna loads (such as dipoles, folded dipoles, or long-wire antennas).
Input Guide
Enter Input Impedance, Output Impedance exactly in the units shown by this balun. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Input Impedance — use Ω.
- Output Impedance — use Ω.
Output Guide
The results describe the calculated balun values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The Balun uses Impedance Ratio = Zout / Zin, Turns Ratio = √(Zout / Zin). Supply Input Impedance (Ω), Output Impedance (Ω) in the displayed units, then use the calculated values as the first engineering target for this waveguide & feedline design or analysis.
Design Notes
A balun matches unbalanced coaxial lines to balanced antenna elements while isolating feedline shield currents to eliminate RFI/TVI and radiation pattern distortion. The required winding turns ratio scales as the square root of the impedance ratio: $N_{\text{out}} / N_{\text{in}} = \sqrt{Z_{\text{out}} / Z_{\text{in}}}$. Common topologies include 1:1 Current (Guanella) baluns for dipole choke isolation, 4:1 Voltage/Current baluns for folded dipoles and off-center fed dipoles (OCFD), and 9:1 or 16:1 ununs for end-fed random wire antennas.
Build and Tuning Notes
When winding toroid or binocular core baluns, select appropriate ferrite materials (such as Mix 31, 43, or 61) based on operating frequency range to maintain high choking impedance without core saturation. Validate impedance transformation and return loss across the target band using a Vector Network Analyzer (VNA) or SWR meter attached to a non-inductive dummy load.
Frequently Asked Questions
What is the difference between a Balun and an Unun?
A Balun connects a BALanced line (like a symmetric dipole or ladder line) to an UNbalanced line (like coaxial cable). An Unun connects an UNbalanced line to another UNbalanced line (such as matching 50 Ω coax to an end-fed vertical antenna).
How is the turns ratio calculated from the impedance ratio?
Because impedance scales with the square of the winding turns ($Z \propto N^2$), the turns ratio is the square root of the impedance transformation ratio: $\text{Turns Ratio} = \sqrt{Z_{\text{out}} / Z_{\text{in}}}$. For a 4:1 impedance balun, the turns ratio is $2:1$.
Why is a 1:1 Current Balun recommended at antenna feedpoints?
Even when no impedance transformation is needed ($50\, \Omega$ to $50\, \Omega$), a 1:1 current balun acts as a common-mode RF choke. It prevents RF currents from flowing back down the outside of the coax shield, eliminating stray RF in the shack and preserving antenna radiation patterns.
What is the difference between Guanella and Ruthroff baluns?
Guanella baluns use transmission-line transformers connected in parallel/series to force equal and opposite currents (ideal for broad bandwidth and high common-mode rejection). Ruthroff baluns use conventional autotransformer windings, which are simpler but less effective at high common-mode isolation.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.