VSWR Input Panel
Choose one calculation path and fill the related inputs only.
Example Data Table
Use these sample cases to validate your installation or compare methods.
| Scenario | Input Method | Input Values | Expected VSWR | Return Loss |
|---|---|---|---|---|
| Near matched feeder | Power | Forward 100 W, Reflected 1 W | 1.22 | 20.00 dB |
| Moderate mismatch | Gamma | |Γ| = 0.3333, Forward 100 W | 2.00 | 9.54 dB |
| Good antenna tuning | Return loss | RL = 14 dB, Forward 50 W | 1.50 | 14.00 dB |
| Reactive load example | Impedance | Z0 = 50 Ω, ZL = 60 + j15 Ω | 1.39 | 15.79 dB |
Formula Used
VSWR links the forward wave to the reflected wave on a transmission line. The calculator uses whichever input path you choose and converts that input into reflection coefficient magnitude first.
|Γ| = √(Pref / Pfwd)when forward and reflected power are known.VSWR = (1 + |Γ|) / (1 - |Γ|)for any passive line with|Γ| < 1.Return Loss = -20 log10(|Γ|)in decibels.Mismatch Loss = -10 log10(1 - |Γ|²)in decibels.Reflected Power % = |Γ|² × 100andDelivered Power % = (1 - |Γ|²) × 100.Γ = (ZL - Z0) / (ZL + Z0)when characteristic impedance and complex load impedance are known.
How to Use This Calculator
- Select the calculation method that matches your available test data.
- Enter only the values needed for that method.
- Click Calculate VSWR to generate results.
- Review the results panel above the form for the main ratios, losses, and power split.
- Use the export buttons to save the result summary as CSV or PDF.
- Compare your outcome with the example table to confirm expected behavior.
Frequently Asked Questions
1. What does VSWR tell me?
VSWR shows how well the load matches the transmission line. Lower values mean less reflected energy, better power transfer, and usually improved transmitter and antenna system performance.
2. Is a VSWR of 1.0 always possible?
A perfect 1.0 match is theoretically possible, but real systems usually land slightly above it because cables, connectors, antennas, and instruments introduce small imperfections.
3. How is return loss different from VSWR?
They describe the same mismatch from different viewpoints. VSWR is a ratio on the line, while return loss expresses reflected behavior in decibels.
4. Why does the calculator ask for optional forward power?
Forward power is optional in gamma, return loss, and impedance modes because it helps estimate reflected watts and delivered watts, not the VSWR value itself.
5. Can reactive impedance affect VSWR?
Yes. Reactive load components change the complex reflection coefficient. That changes magnitude and phase, which can increase VSWR even when resistance looks close to the line impedance.
6. What VSWR level is usually acceptable?
Many practical systems accept values up to 2.0, though exact limits depend on transmitter tolerance, cable loss, safety margin, and application sensitivity.
7. Does cable loss change the interpretation?
Yes. Lossy cables can hide reflected energy at the measurement point. A low reading there may still correspond to a worse mismatch at the antenna.
8. When should I use the impedance mode?
Use impedance mode when you know the line impedance and the complex load impedance. It is useful for design review, matching networks, and antenna modeling.