Method of characterizing the performance of a payload of a satellite in orbit and associated IOT system

A method of characterizing a performance of a payload of a satellite in orbit using a test ground station, comprising:

• the test ground station including at least one first radio-frequency amplifier, and a radio-frequency transmit ground antenna with a first input port of the antenna connected to an output of the at least one first radio-frequency amplifier,
• the payload of the satellite including a first receive satellite antenna for uplink, a second transmit satellite antenna for downlink, and a transponder connected between the first receive satellite antenna and the second transmit satellite antenna,
• the transponder including a second radio-frequency input port connected to an output port of the receive satellite antenna, and at least one second amplifier being configured to amplify in an input portion of an uplink transponder or in the whole of transponder signals in a receive frequency band of the transponder, according to a linear amplification mode and with a fixed gain that can be remote-controlled and included in a gain range varying between a first lower gain Gmin and a second higher gain Gmax inclusive,
• the method further comprises a supply step of:
• generating a test thermal noise with the at least one first radio-frequency amplifier at the input of a transmit ground antenna, the test thermal noise having a bandwidth greater than or equal to the receive band of the transponder and a power spectral density of which is adjusted to a test thermal noise reference power spectral density Dref such that a ratio of the spectral density of the test thermal noise, received from the test ground station when the thermal noise spectral density that it transmits is equal to the reference spectral density Dref, and received at the input of the transponder, to a thermal noise floor spectral density generated by the satellite alone internally and natural thermal noise of the Earth at the input of the transponder is greater than or equal to a first threshold Ds1 equal to 10 dB.