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operations:tsys_method

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+ | ====== Tsys and Tcal calculations based on Y-factor data ====== | ||

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+ | System temperature includes a number of contributions: receiver, atmosphere, CMB, plus antenna effects such as groundspill, surface imperfections etc. It can be measured by comparing observations of the sky and of a known load, | ||

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+ | (T<sub>load</sub> + T<sub>LNA</sub>) / T<sub>sys</sub> = Y | ||

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+ | where the measured Y-factor is given in terms of the difference in measured power (in decibels), | ||

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+ | Y = 10<sup>0.1(P<sub>load</sub>-P<sub>sky</sub>)</sup> | ||

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+ | Typical values are P<sub>load</sub>-P<sub>sky</sub> = 4.5 - 6 and hence Y = 2.8 - 4. | ||

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+ | Hence T<sub>sys</sub> = (T<sub>load</sub> + T<sub>LNA</sub>) / Y | ||

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+ | Load temperature is just the ambient temperature (in Kelvin), and the LNA temperature is assumed to be 45K. | ||

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+ | With the system temperature known, there are two ways of calculating the noise diode (cal) temperature. When measurements of the sky and load are both made with the diode included, | ||

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+ | T<sub>cal</sub> = (T<sub>load</sub> + T<sub>LNA</sub> - Y T<sub>sys</sub>) / (Y-1) | ||

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+ | When the diode in included in the load measurement, but not in the sky-only measurement, | ||

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+ | T<sub>cal,2</sub> = Y T<sub>sys</sub> - T<sub>load</sub> - T<sub>LNA</sub> | ||

/home/www/auscope/opswiki/data/pages/operations/tsys_method.txt · Last modified: 2011/10/26 06:37 (external edit)