Status of EVN Amplitude Calibration 
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Session 3/2010
---------------

The following table shows the median absolute amplitude error for EVN stations in the last session of 2010 (Oct/Nov). These results were derived from the pipeline amplitude self-calibration results of all the EVN experiments including NME experiments. Note that Ur, Sh, Nt, and Jb1 were out. The number in brackets after each entry is the number of experiments that were used to determine the median error for that entry.

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Station     18 cm        5 cm       {1.3 cm }
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Jb          0.09(11)                {4.31(3)}
Ef          0.04(9)     0.03(4)     {0.09(4)} 
Mc          0.13(11)*   0.06(4)     {0.12(4)}
On          0.21(10)*   0.15(4)     {0.34(4)}
Tr          0.08(10)    0.04(4)     
Wb          0.03(11)    0.10(4) 
Ys                      0.03(4)     {0.11(4)}  
Hh          0.03(3)
Bd          0.06(8)    
Sv          0.09(6)
Zc          0.27(7)*
Mh                                  {0.37(2)}
Ro                                  {0.08(1)}
==============================================


Note that Ur, Sh, Nt, and Jb1 were out and Jb2 C-band receiver was broken after N10M2. The blank entries indicates insufficient data. The numbers above are the median absolute error in the antenna gain amplitude (as calculated from pipeline amplitude self calibration). A value above 0.1 indicates a significant error which should be investigated. In addition to the absolute errors summarized here, the EVN pipeline provides details on every experiment processed at JIVE including the sign and time variability of the errors. In each experiment, the self-calibration results of a bright and compact source were used to get the reliable results.


*On: It was reported that the new broad-band IF system was too sensitive to RFIs and could not work properly. Due to the problem, high Tsys and varying correlation amplitude across subbands were seen in the pipeline results of the 18cm experiments. After the session, the problem has been solved. Bad weather may affect the calibration at 5cm.  
      
*Mc: The results may be related to the bad amplitude calibration of Onsala.     

*Zc: No Tsys data available. 


*QUAZAR stations
Through the pipeline results, we tried the following value: SEFD = 400 Jy for Zc; SEFD = 300 Jy for both Bd and Sv to quickly make antab files. Before making Session 2/2011 antab files, J. Yang has reduced N11L3 and N11C1 data and determined the new SEFDs.  

18cm -- Zc: 300 Jy, Bd: 330 Jy, Sv 360 Jy.
6cm  -- Zc: 400 Jy, Bd: 200 Jy, Sv 250 Jy.


Amplitude calibration at 1.3cm
Bad amplitude calibration is well known for a long time. No Tsys data available from Jb2 although the extracted tpi (total power) data looked OK. Note
that the gain determination of Mc and On may be significantly affected by the bad ampliutde calibration of Jb2 due to their low sensitivity. To get a meaningful number for each station, it is required to have opacity-free gain curve, good weather, a bright and compact calibrator, and to flag out any bad data.   


Jun YANG for the Science Operation and Support Group (JIVE)