[evlatests] P-band flux density ratios -- early results

[Rick Perley]

    The data Frazer took yesterday morning is of quite nice quality 
(other than a couple of antennas) -- certainly good enough to compare 
ratios to the ~20 years of 'flux density' data.  I did a 'quick and 
dirty' calibration of the flux densities of the four 'standard' sources 
he included in his test run. 

    To do this, I extracted a narrow subband of width 16 MHz, centered 
near 325 MHz.   Following bandpass calibration (absolute, not 
normalized), I derived the flux densities of 3C48, 3C138, and 3C196, 
using 3C147 as the reference -- using only 'GETJY' on the antenna gain 
solutions.  The stability of the gains was, overall, very impressive!  
Only a few antenna-IFs showed temporal variances more than a few 
percent.  Using a subset of the most stable antennas, I generated the 
following ratios to 3C196.   Shown below are the 'flux density' ratios, 
at 327.5 MHz, over the many years since the original P-band system went 
up. 

Ratio                Now      89     92      95      99      00      01  
    03      04      06      07      08
--------------------------------------------------------------------------------------------------------------------
3C48/3C196    .924     .926   .930   .925   .935   .928   .954   .919   
.944   .943   .948   .934

3C138/3C196  .352     .421  .405   .390    .397   .398   .395   .382  
.385    .367   .370   .350

3C147/3C196 1.137  1.150 1.163 1.151 1.149 1.149 1.152 1.154 1.170 1.165 
1.167 1.168
----------------------------------------------------------------------------------------------------------------------

    These are, I think, quite nice results.  3C147 seems a little low 
now compared to what we did in the past.  3C138 shows pretty clear 
evidence of a declining flux density -- this is not surprising as it is 
a known variable source.  3C48 seems fairly stable. 

    A brief look at Cas A and Cyg A show the 'LCP' side (horizontal or 
vertical?) gives quite good values, but the 'RCP' side (vertical or 
horizontal?) shows much greater variances.  I'll do some poking around 
to find which antennas are responsible ...