# ITU-R Recommendation P.372-16 — Radio noise > [!abstract] Legend > - 🟢 **Green** (`tip` / `note` / `success`) — informational, definitions, summaries > - 🟡 **Yellow** (`warning`) — CRITICAL: contradictions, methodological gaps > - 🔴 **Red** (`danger` / `error`) — CRITICAL: structural admissions, factual errors > - ⬜ **Grey** (`quote`) — verbatim source text ## Bibliographic Info - **Year:** 2022 - **Author:** International Telecommunication Union, Radiocommunication Sector (ITU-R) - **Title:** Recommendation ITU-R P.372-16: Radio noise - **Publication / Source:** ITU, Geneva. P Series (Radiowave propagation). 104 pages. - **URL / Archive / DOI:** itu.int/rec/R-REC-P.372 - **Accessed:** 2026-05-20 ## Source Summary Recommendation P.372 is the ITU-R reference for radio noise. It tabulates and parametrises the external noise an antenna collects from atmospheric, man-made, and extra-terrestrial sources across the radio spectrum. For the Battle of the Beams analysis the operative part is Part 4, the brightness temperature due to extra-terrestrial sources, which gives a closed-form median noise figure for galactic noise below about 100 MHz. At 31.5 MHz this galactic figure is the dominant external noise term and sets the operative receiver noise floor. > [!tip] Variable definitions > - $F_{am}$ — median external noise figure, dB above the thermal noise floor $kT_0B$ > - $f$ — frequency, MHz > - $foF2$ — F2-layer ordinary-wave critical frequency, MHz ## Key Claims From the Source ### Claim 1 — galactic noise median figure below 100 MHz ![[2022_ITU-R_P372-16_p16_eq13_galactic_noise.png]] > [!quote] Direct quote (Part 4, §4.1, p. 16, equation 13) > "For frequencies up to about 100 MHz, the median noise figure for galactic noise for a vertical antenna, neglecting ionospheric shielding, is given by: > $F_{am} = 52 - 23 \log f$ (dB) > where: $f$: frequency (MHz). The decile deviations of the mean galactic noise power are 2 dB." > [!tip] Summary > Below roughly 100 MHz the galactic background, the broad belt of Milky Way emission, dominates the external noise a vertical antenna collects. P.372 gives its median figure in closed form, $F_{am} = 52 - 23\log f$ dB, with upper and lower decile spreads of 2 dB. At 31.5 MHz this evaluates to about 17.5 dB above the thermal floor, which exceeds a typical receiver noise factor, so galactic noise is the term that fixes the operative noise floor in the BotB link budget. ## Equations and Mathematical Material Galactic noise median figure (P.372-16 Eq. 13, p. 16): $F_{am} = 52 - 23 \log_{10} f \quad \text{(dB)}, \qquad f \text{ in MHz}$ The total operative external-plus-receiver noise figure used in the BotB noise floor is the larger of this galactic figure and the receiver noise factor (see [[1944_Friis_Noise_Figures_Radio_Receivers]]). The thermal reference floor it sits above is $kTB$ (see [[1928_Nyquist_Thermal_Agitation_Electric_Charge]]). ## Figures / Tables / Diagrams Screenshot above: ITU-R P.372-16 p. 16, Part 4 §4.1, showing equation (13) for galactic noise. ## Relevant Quotes See Claim 1. ## Backlinks - [[Knickebein_Propagation_Null]] - [[1928_Nyquist_Thermal_Agitation_Electric_Charge]] - [[1944_Friis_Noise_Figures_Radio_Receivers]] ## Tags #source