Ham Radio Tools

SWR ↔ Return Loss

Quick conversion between common mismatch metrics.

From SWR

Return Loss—
Reflection coeff |Γ|—
Reflected power—
Mismatch loss—

From Return Loss

SWR—
|Γ|—
Reflected power—
Mismatch loss—

Why Return Loss matters

SWR is the traditional ham-radio metric, but modern instruments often display Return Loss in decibels. A higher Return Loss number is better (more power is accepted by the antenna). Rough equivalents: SWR 1.5 ≈ 14 dB RL, SWR 2.0 ≈ 9.5 dB RL, SWR 3.0 ≈ 6 dB RL. Most solid-state radios begin to reduce power above SWR 1.5–2.0, so keeping Return Loss above about 10–14 dB is a practical target.

Reflection coefficient |Γ| is the underlying quantity: the fraction of the voltage wave that is reflected. SWR = (1+|Γ|)/(1-|Γ|) and RL = –20 log10|Γ|.

Use the conversion when checking measurements

Standing-wave ratio and return loss describe the same mismatch from different viewpoints. SWR compares the maximum and minimum voltage along a line, while return loss expresses the reflected wave as a logarithmic loss relative to the incident wave. A perfect match has an SWR of 1:1 and an ideal return loss tending toward infinity. As mismatch increases, SWR rises and return loss falls. The conversion is useful when reading equipment specifications because instruments and data sheets do not always use the same metric. Remember that SWR alone does not tell you whether the load is inductive, capacitive or resistive, and a low SWR at the transmitter does not prove that the antenna itself is resonant if a tuner sits between the transmitter and feedline. Use an analyser or other measurement method when the actual impedance is required. The converter is therefore best viewed as a translation tool between two standard mismatch measures.

Assumptions & limitations

Measurement gotchas

Coax LossAntenna TrimmerEnd-Fed / EFHWMagnetic Loop