SWR and Reflected Power Calculator

Standing Wave Ratio (SWR) measures how well matched an antenna system is to the transmission line. A perfect match gives SWR = 1:1. Mismatches create standing waves on the feedline, wasting power.

SWR from impedance: Reflection coefficient: Γ = (Z_load - Z_line) / (Z_load + Z_line) SWR = (1 + |Γ|) / (1 - |Γ|)

Reflected power percentage: P_reflected = |Γ|² × 100%

SWR guidelines for amateur radio:

• SWR 1:1 — Perfect (theoretical)
• SWR up to 1.5:1 — Excellent, essentially no practical loss
• SWR 1.5–2.0:1 — Good, most modern transceivers handle this without protection
• SWR 2.0–3.0:1 — Acceptable, some power loss in feedline
• SWR 3.0–5.0:1 — Poor, significant feedline loss, transmitter may reduce power
• SWR above 5:1 — Bad, antenna needs retuning

Power loss in dB: Return loss (dB) = -20 log₁₀(|Γ|)

Practical notes: Most modern HF transceivers have built-in ATUs (antenna tuning units) that can match loads up to SWR 3:1. Feedline type matters — low-loss ladder line tolerates high SWR much better than coax. High SWR in coax significantly increases feedline heating and signal loss.