## How to Calculate the RMS From a Dual-Polarization Measurement When the System Temperatures Differ

9 Apr 2017, 16:02 UTCQuestion: Nowadays, the receiver of radio telescope could receive 2 polarizations (e.g. LC and RC). Then, when we use the telescope to measure the total flux density of a radio source (here, do not measure the polarization of the source), whether we still only use one polarization to do that (?) In this case, suppose the bandwidth of *each polarization* is DeltaV, the radiometer equation would be sigma= Tsys/sqrt(DeltaV*t), Tsys is the system temperature measured in this polarization, and t is the integrated time. But, whether we could use the two polarizations together to measure the total flux density (?) if so, whether the radiometer equation would be sigma= Tsys/sqrt(2*DeltaV*t) ? But the system temperature would be different in the two polarization channels, and how to sum the signals (?) I am very confused of this, thanks for help — Hongmin

Answer: Let me answer your question by answering a more general question… I maintain a web page with a number of radio astronomy tutorials which describe various aspects of radio astronomy measurement and techniques. One of the tutorials is on “The Radiometer Equation for Position Switched Measurements”. This tutorial derives the radiometer equation and provides an example where one ...