📊 VSWR Converter

Understanding VSWR and Related Parameters

VSWR (Voltage Standing Wave Ratio) measures how well a load (antenna) matches the transmission line impedance. A perfect match is 1:1, meaning all power is delivered to the load with no reflections. VSWR is the most common metric used by amateur radio operators because it's easy to measure with an SWR meter.

Return Loss is the preferred metric in professional RF engineering. It expresses how much of the incident signal is reflected back, in decibels. Higher return loss is better — 20 dB means only 1% of power is reflected, while 10 dB means 10% is reflected. The relationship is: RL(dB) = -20 × log10(|Γ|)

Reflection Coefficient (Γ) is the fundamental quantity. It's the ratio of reflected voltage to incident voltage. For a real impedance Z connected to a system of impedance Z0: Γ = (Z - Z0) / (Z + Z0). VSWR is then (1 + |Γ|) / (1 - |Γ|).

Mismatch Loss is the additional power lost due to reflections, beyond the matched transmission line loss. It represents power that never reaches the load because it bounces back and forth, dissipating in the cable. For VSWR 2:1, mismatch loss is about 0.51 dB. For VSWR 3:1, it's about 1.25 dB.

Practical Reference Table

• VSWR 1.0: Perfect match — 0% reflected, ∞ dB return loss, 0 dB mismatch loss
• VSWR 1.5: Good match — 4% reflected, 14.0 dB return loss, 0.18 dB mismatch loss
• VSWR 2.0: Fair match — 11.1% reflected, 9.54 dB return loss, 0.51 dB mismatch loss
• VSWR 3.0: Poor match — 25% reflected, 6.02 dB return loss, 1.25 dB mismatch loss
• VSWR 6.0: Bad match — 51% reflected, 2.92 dB return loss, 3.02 dB mismatch loss
• VSWR 10.0: Very bad — 67% reflected, 1.74 dB return loss, 4.81 dB mismatch loss
• VSWR ∞: Open/short circuit — 100% reflected, 0 dB return loss, ∞ dB mismatch loss

FAQ

What VSWR is acceptable? For HF transmitters, up to 2:1 is generally acceptable. For VHF/UHF, aim for 1.5:1 or better. For receive-only antennas, higher VSWR matters less. Modern solid-state transmitters often fold back power above 2:1 to protect the finals.

Does a tuner reduce VSWR? A tuner at the transmitter makes the transmitter see a good match, but it does NOT reduce feedline losses caused by high SWR. The mismatch loss still exists in the cable. A tuner at the antenna feedpoint is the only way to eliminate mismatch loss.

Why does my antenna show different VSWR on different bands? A dipole is resonant on its fundamental frequency and odd harmonics. On other bands, its impedance is reactive and the VSWR will be high. This is normal and expected.