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operations:tsys [2011/03/02 04:11] Stas Shabala |
operations:tsys [2011/10/26 06:37] |
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- | ====== Y-Factor and Tsys Measurements ====== | ||
- | 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> | ||
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- | Measurements for Feb 28 on the Hobart 12m are given below. | ||
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- | {{:operations:hb12_tsys.xls|Hb12_Tsys.xls}} |