lbn gain curves after horn focus moved.


link to gain curve plots

    The lband narrow (lbn) horn was lowered 3.84 inches on 21aug02 to put the phase center in the correct location. This changed the gain as a function of azimuth and za. Calibration scans from 21aug02 to 09sep02 were used to create a new set of gain curves. The final fits were done only as a function of za. This was mainly because of the limited az coverage. I tried fitting to both az and za and it showed a slight improvement in the residuals. With the feed no longer far out on the edge of the focus curve, small changes in focus will no long affect the gain as much as before.

    Gain curves were fit to lbn data  from 01sep01 to 02sep02. There were about 168 points at each of the 4 frequencies. The cal values used were those from 28jan02. The plots show the gain data (black) and the fits (red) for the 4 frequencies: 1300, 1375, 1415, and 1500 Mhz.

    The  largest source of error in the gain curves is probably the cal values (especially at 1300 and 1500 Mhz where the receiver starts to degrade). The  system performance computed from this data set (including the SEFD which is independent of the cals) is also available for inspection.

    The idl routines gainget() or corhgainget() will now return the lbn gain for data after 20aug02 using these fits.. The coefficients can be found in the ascii file  data/gain.datR6 (this is provided in the AO idl distribution for correlator routines). You can also find a copy of it at AO in /home/phil/idl/data/gain.datR6.

processing: x101/lb/sep02/