[evlatests] Tcal accuries at P-band

[Rick Perley]

     A recent test at P-band observed both Cygnus A and some good 
calibrators (3C48 and 3C380).  The primary goal was to test linearity of 
the system -- results for this will be presented later (but the news is 
very good).

     Here I report on the accuracy of the Tcal values.

     All antennas except ea13 and ea18 had good values of PDif.  If the 
Tcal values are correct, and the efficiencies utilized are correct, the 
visibility data for the calibrators, following application of the 
switched power should equal the known source flux densities.

     For this test, I chose a single subband, at 312 MHz.  (Reason -- 
this subband had the least RFI).   After basic editing, the switched 
powers were applied, and CALIB run on the two calibrators listed above.

     The mean solutions (for 'R' and 'L') were within 5% of 1.0. That's 
the good news.

     The not-so-quite good news is that there is a large scatter. Below 
are the CALIB gains needed to bring the data into alignment with the 
correct flux densities.  Presuming the utilized efficiencies are 
correct, and are the same for every antenna, the error is in the values 
of the Tcals.  The needed correction to the Tcal values is the square of 
the gain factor listed.  Hence, if the gain factor is 1.1, then the Tcal 
value should be increased by 1.21.

Antenna      Gain Factor

1R                     1.08
1L                      1.07
2R                     1.03
2L                      0.87
3R                     1.05
3L                      0.95
4R                     1.02
4L                      0.75
5R                     0.90
5L                      0.86
6R                      0.98
6L                      1.06
7R                     1.02
7L                      0.92
8R                     out
8L                      out
9R                     1.09
9L                      0.84
10R                    1.50
10L                    1.30
11R                    out
11L                     out
12R                    1.23
12L                    1.36
13R               no PDif
13L                no PDif
14R                   0.97
14L                   0.72
15R                   1.20
15L                    0.84
16R                   1.20
16L                    0.95
17R                   0.92
17L                    1.00
18R                   1.04
18L              PDif broken
19R                   1.08
19L                    0.67
20R                   1.10
20L                    1.17
21R                    1.14
21L                    1.03
22R                   0.94
22L                    0.90
23R                    1.05
23L                    1.07
24R                   1.12
24L                     1.13
25R                    1.27
25L                     1.50
26R                    0.90
26L                     0.97
27R                    0.93
27L                     1.05
28R                    0.93
28L                     0.91