Terminology: EIRP, G/T, Input Back-Off, Output Back-Off

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EIRP: Used to indicate the power transmitted from an antenna. EIRP=Power +Antenna Gain, Both EIRP and Power is expressed in dBW and Gain in dBi.
G/T: It is the figure of merit for an earth station and is expressed as dB/K (dB per K).
G/T= Antenna Gain-10*Log (System Noise Temperature) The higher the better-G/T can be raised by using a higher gain antenna or a lower temperature LNA. The earth station G/T determines the received carrier to noise ration. Increasing station G/T will increase the C/N of the received carrier.


Input Back-Off (IPBO): The level of a signal at the input of an amplifier relative to that level at the input that would result in the maximum possible output level. For example, if an input level of -20dBm causes max output and the actual input level is -25dBm, the IPBO is 5dB. Both IPBO and OPBO are commonly used to determine the operating levels in a satellite transponder TWTA.


Output Back-Off (OPBO) The level of a signal at the output of an amplifier relative to the maximum possible output level. For example, if a maximum output level is +40dBm and the measured output level is +34dBm, the OPBO is 6dB. 

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