Editing Return loss (section)

== Sign ==
As defined above, RL will always be positive, since ''P''<sub>r</sub> can never exceed ''P''<sub>i</sub>. However, return loss has historically been expressed as a negative number, and this convention is still widely found in the literature.<ref name=Bird>Trevor S. Bird, [https://ieeexplore.ieee.org/document/5162049/;jsessionid=2EF091A77801B0C8C3DE98C8B15CD450?arnumber=5162049 "Definition and Misuse of Return Loss"], ''IEEE Antennas & Propagation Magazine'', vol.&nbsp;51, iss.&nbsp;2, pp.&nbsp;166–167, April 2009.</ref> Strictly speaking, if a negative sign is ascribed to RL, the ratio of ''reflected'' to ''incident'' power is implied:
: <math>\text{RL}'(\text{dB}) = 10 \log_{10} \frac{P_\text{r}}{P_\text{i}},</math>
where RL′(dB) is the negative of RL(dB). 

In practice, the sign ascribed to RL is largely immaterial.  If a transmission line includes several discontinuities along its length, the total return loss will be the sum of the RLs caused by each discontinuity, and provided all RLs are given the same sign, no error or ambiguity will result.  Whichever convention is used, it will always be understood that ''P''<sub>r</sub> can never exceed ''P''<sub>i</sub>.