Return Loss
Return loss is the dB expression of the ratio of the power reflected from the antenna to the incident power, and it converts one-to-one with SWR: 1.5:1 SWR corresponds to about 14 dB, 2:1 to about 9.5 dB and 3:1 to 6 dB of return loss. The larger the value, the less the reflection, meaning the better the match.
SWR and return loss give the same information on two different scales. Measuring instruments usually show both; since return loss is in dB, it goes into a link budget calculation more easily.
- Interpretation: values above 10 dB are considered acceptable for most short range device applications, while below 6 dB is considered problematic.
- As a diagnostic tool: note the value measured while the antenna and cable are sound; if a later measurement deviates from that reference, there is a mechanical problem.
- It is frequency dependent: the same antenna can give a good value in the middle of the band and a poor one at the edge.
Reading this value in the field is not possible without a dedicated instrument, but the causes of degradation can be found by eye: a crushed cable, a broken antenna, a loose or oxidised connector. These three checks catch most problems without measuring the return loss.
Context where this term is used: Wireless remote control installation: pairing, relay, safety