VSWR Calculator
Calculate VSWR, reflection coefficient, return loss and mismatch loss from power readings, load impedance or Γ.
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What this tool does
Calculate VSWR, reflection coefficient, return loss and mismatch loss from power readings, load impedance or Γ. The impedance mode assumes a purely resistive load. Complex loads require magnitude Γ from a network analyser or Smith chart.
How to use the VSWR Calculator
- Enter or select input method.
- Enter or select forward power (w).
- Enter or select reflected power (w).
- Enter or select load resistance (ohms).
- Enter or select line impedance z0 (ohms).
- Enter or select reflection coefficient γ (0 to <1).
- Read the calculated result; change any measurement to compare alternatives.
Formula
Γ from powers: √(Pr/Pf); from impedance: (ZL − Z0)/(ZL + Z0); VSWR = (1 + Γ) ÷ (1 − Γ); return loss = −20·log10(Γ)
- mode
- Input method
- fwd
- Forward power (W)
- refl
- Reflected power (W)
- zload
- Load resistance (ohms)
- z0
- Line impedance Z0 (ohms)
- gammaIn
- Reflection coefficient Γ (0 to <1)
The impedance mode assumes a purely resistive load. Complex loads require magnitude Γ from a network analyser or Smith chart.
Worked example
For vswr calculator, the following measurements illustrate the exact method: Input method: power; Forward power (W): 100; Reflected power (W): 4; Load resistance (ohms): 75; Line impedance Z0 (ohms): 50; Reflection coefficient Γ (0 to <1): 0.2.
Inputs
- Input methodForward & reflected power
- Forward power (W)100
- Reflected power (W)4
- Load resistance (ohms)75
- Line impedance Z0 (ohms)50
- Reflection coefficient Γ (0 to <1)0.2
Result
- VSWR1.5
- Reflection coefficient Γ0.2
- Return loss (dB)13.98
- Reflected power (%)4
- Mismatch loss (dB)0.18
Results explained
- VSWR
- VSWR from the formula above. The impedance mode assumes a purely resistive load. Complex loads require magnitude Γ from a network analyser or Smith chart.
- Reflection coefficient Γ
- Reflection coefficient Γ from the formula above. The impedance mode assumes a purely resistive load. Complex loads require magnitude Γ from a network analyser or Smith chart.
- Return loss (dB)
- Return loss (dB) from the formula above. The impedance mode assumes a purely resistive load. Complex loads require magnitude Γ from a network analyser or Smith chart.
- Reflected power (%)
- Reflected power (%) from the formula above. The impedance mode assumes a purely resistive load. Complex loads require magnitude Γ from a network analyser or Smith chart.
- Mismatch loss (dB)
- Mismatch loss (dB) from the formula above. The impedance mode assumes a purely resistive load. Complex loads require magnitude Γ from a network analyser or Smith chart.
Frequently asked questions
Γ = √(reflected ÷ forward), then VSWR = (1 + Γ) ÷ (1 − Γ). With 100 W forward and 4 W reflected, Γ = 0.2 and VSWR = 1.5.
Below 1.5 is good, 2.0 is a common working limit (about 11% of power reflected), and above 3 most transmitters fold back power or risk damage. Antenna specs and radio manuals state their own limits.
Return loss = −20 × log₁₀(Γ) in dB — how far below the forward signal the reflection sits. Γ = 0.2 gives about 14 dB return loss.
Γ = (ZL − Z0) ÷ (ZL + Z0) for a resistive load. A 75 Ω load on a 50 Ω line gives Γ = 0.2 and VSWR 1.5. Reactive loads need the complex form; this tool uses the resistive magnitude.
Not by itself — a dummy load has perfect VSWR and radiates nothing. VSWR only measures the match; efficiency and pattern are separate questions.