ITU-R Recommendation Series
ITU-R Recommendations are grouped into lettered series by subject, such as BO (satellite delivery), F (fixed service), M (mobile), P (propagation), S (fixed-satellite) and SM (spectrum management).
What is ITU-R Recommendation Series?
Other series include BS and BT (sound and television broadcasting), RA (radio astronomy), RS (remote sensing), SA (space applications), SF (sharing between fixed-satellite and fixed services), SNG (satellite news gathering), TF (time signals) and V (vocabulary). For example, ITU-R P.525 covers free-space attenuation.