About this tool
The standing wave ratio (SWR or VSWR) shows how well an antenna or load is matched to the cable and transmitter. At 1 : 1 all power is accepted; with a poor match part of it travels back as reflected power. The return loss (S11) and the reflection coefficient Γ carry the same information.
The SWR calculator converts between these three quantities and shows the share of reflected power and the mismatch loss. It can also compute the SWR from forward and reflected power as shown by an SWR meter, or from a complex load impedance R + jX at 50 Ω, 75 Ω or a custom line impedance.
The advanced parameters show how a lossy cable makes the SWR measured at the transmitter look better, and how much extra loss the standing wave causes. Find the cable loss itself with the Coax Cable Loss Calculator. Everything is calculated in your browser.
How it works
- Choose your starting point at the top: SWR or return loss, forward and reflected power, or an impedance.
- Enter the values and read SWR, return loss, reflection coefficient, reflected power and mismatch loss.
- Turn on the advanced parameters and enter the cable loss to see the SWR at the transmitter and the total loss.
Frequently asked questions
What is a good SWR?
Below 1.5 : 1 an antenna counts as well matched: only 4 % of the power is reflected and the mismatch loss stays below 0.2 dB. Up to 2 : 1 (11 % reflected, 0.5 dB) is fine for most transmitters, but many transceivers start reducing power around 2 : 1. Above that, check antenna, cable and connectors.
How do I convert SWR to return loss?
First find the reflection coefficient: |Γ| = (SWR − 1) / (SWR + 1). The return loss is then −20·log10(|Γ|). SWR 2 gives |Γ| = 0.333 and 9.54 dB, SWR 1.5 gives 0.2 and 13.98 dB. The other way round, SWR = (1 + |Γ|) / (1 − |Γ|).
How is the SWR calculated from forward and reflected power?
The reflection coefficient is the square root of the ratio of reflected to forward power: |Γ| = √(Pr / Pf). With 100 W forward and 4 W reflected, |Γ| = 0.2 and the SWR is 1.5 : 1. The antenna then receives 96 W (without cable loss).
Why does my SWR meter at the transmitter show a better value than at the antenna?
The cable attenuates the reflected wave twice, on its way to the antenna and back. A cable with 3 dB loss therefore improves the return loss at the transmitter by 6 dB; SWR 3 at the antenna becomes about 1.7 at the transmitter. The power is still lost – in the cable. The advanced parameters calculate both.