RF Toolkit ยท IEEE Std 181
Calculator VSWR / Return Loss
Enter a value in any unit, the others convert automatically: VSWR, Return Loss (dB), Reflection Coefficient, Mismatch Loss (dB).
Typical Cell Site Thresholds
| VSWR | Return Loss | Mismatch Loss | Status |
|---|---|---|---|
| 1.0 | inf | 0 dB | Perfect |
| 1.2 | 20.83 dB | 0.036 dB | Excellent |
| 1.5 | 13.98 dB | 0.177 dB | Good (site limit) |
| 2.0 | 9.54 dB | 0.512 dB | Alarm |
| 3.0 | 6.02 dB | 1.249 dB | Fault |
Frequently Asked Questions
What is VSWR?
VSWR (Voltage Standing Wave Ratio) measures the impedance match between a transmission line and its load. A value of 1:1 means perfect match (no reflection). A high value means mismatch: part of the power is reflected, does not radiate from the antenna, and can damage the transmitter. Typical acceptable limit for a cell site: VSWR < 1.5:1, alarm at 2:1.
How do you convert VSWR to Return Loss?
Return Loss (dB) = -20 x log10(|reflection coefficient|) = -20 x log10((VSWR - 1) / (VSWR + 1)). VSWR 1.5 corresponds to Return Loss 13.98 dB. VSWR 2 corresponds to 9.54 dB. VSWR 3 corresponds to 6.02 dB. The higher the Return Loss, the better the match.
What is Mismatch Loss?
Mismatch Loss is the fraction of power lost due to reflection: Mismatch Loss (dB) = -10 x log10(1 - |reflection coefficient|^2). For VSWR 2, you lose approximately 0.51 dB. For VSWR 3, approximately 1.25 dB. This is a loss often underestimated by technicians because it adds to cable losses.
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