The new gain is now 10.5 K/Jy flat out to 15 degrees and then starts dropping because of the za spill over (actually it should start dropping a bit higher in za). The absolute gain value is as certain as the flux and cals. The important change is that the gain is no longer a function of za below za=15. Prior to the move the gain had a linear za dependence all the way down to za=0. This was also seen in the gain curve measurement done for lbw back in sep01 (-.1 K/Jy per deg za see figure 3). The linear dependence was probably being caused by the focus error in the rails (green lines). The 0 to 2" rail error vs za should not affect lbn too much. Adding 3.84" would make the 0 to 2" ramp an appreciable error (this sounds good, but our current model of pitch, roll, and focus does not place the rail ramp at the azimuth of this source !).
Fig 1 top is the gain [K/Jy] before (black) and after (red) the move. This includes rise and set.
Fig 1 bottom is the fractional gain change (new/old)-1.
Fig 2 shows the gain,Tsys,Sefd, and average beam widths before (black) and after (red). Fig 3 has the coma, first sidelobe height, Main beam efficiency, and main beam + 1st sidelobe efficiency. Fig 4 plots the pointing error before (black) and after (red). The bottom plot shows the change in pointing error.
The increase in gain must come from somewhere. Looking at fig 2, the average beam width actually increased a bit after the focus move. On figure 3, the coma parameter has not changed a lot. The only difference seems to be that the first sidelobes after the move have decreased.
The system temperature also looks like it has increased by a bit (although we probably need more measurements to verify this since the weather conditions were not identical on the two days).
The pointing error for azimuth and setting za have change by up to 10 asecs. If we had just moved the horn, you would not expect an az,za dependence to the pointing errors. If the fitting is working differently because the beam shape has changed as a function of az,za then this could explain it. The other possibility is that the before data was taken in intermittent light rain (although we never lost the distomats and tiedown average height tracking). It may be that the moisture may have caused the cables to stretch unevenly. For lband this pointing error is probably not significant.
The other kildal horns should probably also be moved. The cband receiver also shows a linear za dependence with gain. The only question with cband is that the cband focus curve (red line bottom plot) shows that its current focus is close to 1256.35 feet. This is the location where we are currently keeping the average height of the platform. Moving the horn lambda/2. may make things worse.processing: x101/020819/doit.pro, doplot.pro