dB rn : A symbol for "decibels above reference noise," a unit measuring noise levels in telecommunications. The usual reference level is -90 dB m, which is equivalent to a power of 1 picowatt (1 pW). For example, 50 dB rn equals -40 dB m
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}