ISO/TC 211 Multi-Lingual Glossary of Terms (MLGT)

Note 1 to entry: This includes two terms: the noise coming from the environment attenuated by the antenna Ohmic efficiency and the thermal noise added by the antenna Ohmic losses. In the Rayleigh-Jeans approximation, the following formula applies:${\displaystyle T_{\text{A},\text{out}}\left({\Omega }_0\right)={\eta }_{\Omega }{T}_{\text{A}}\left({\Omega }_0\right)+\left(1-{\eta }_{\Omega }\right)T_{\text{p}}}$ where ${\displaystyle T_{\text{A}}}$ is the antenna apeture temperature; ${\displaystyle T_{\text{p}}}$ is the physical temperature of the antenna; ${\displaystyle {\Omega }_0}$ is the Ohmic loss; ${\displaystyle {\eta }_{\Omega }}$ is the Ohmic efficiency of the antenna.

Note 2 to entry: The antenna output temperature (${\displaystyle T_{A,out}}$ ) is related to the input noise temperature of the receiver as shown in the following formula: ${\displaystyle T_{\text{rec},\text{in}}=\frac{\text{h}\nu }{{\text{e}}^{\text{h}\nu /\text{k}{T}_{A,\text{out}}}-1}}$ where ${\displaystyle T_{\text{rec},\text{in}}}$ is the input noise temperature of the receiver; ${\displaystyle \text{h}}$ is the Plank's constant (${\displaystyle 6.62607\times {10}^{-34}\text{J}\cdot \text{s}}$ ); ${\displaystyle \nu }$ is the frequency in Hz; ${\displaystyle \text{k}}$ is the Boltzmann's constant (${\displaystyle 1.38064852\times {10}^{-23}\text{J}/\text{K}}$ ); ${\displaystyle \text{e}}$ is the base of natural logarithm.