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operations:tsys [2011/03/02 01:22] Jim Lovell created |
operations:tsys [2011/03/08 03:01] Jim Lovell |
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====== Y-Factor and Tsys Measurements ====== | ====== Y-Factor and Tsys Measurements ====== | ||
- | {{:operations:microsoft_word_-_vlbi_log_file.docx.pdf|My PDF file}} | + | |
+ | ===== Calculation ===== | ||
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+ | A [[operations:tsys_method|description of the method used to calculate Tsys and Tcal]] | ||
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+ | ===== Results ===== | ||
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+ | A spreadsheet containing data and calculations is in {{:operations:hb12_tsys.xls|Hb12_Tsys.xls}}. | ||
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+ | The following is a summary of the data so far | ||
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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> | ||
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