pointing/gain changes from tertiary motor installation.

aug 2001

     The tertiary drive motors were installed on 31july01. Turret scans were taken before and after the installation to ensure that the tertiary was positioned correctly. The sband narrow system was used at 2380 Mhz. The tiedowns were tracking the average height of the platform during these measurements. The "before" runs were done on 30july01. The "after" runs were done on 01aug01 and 09aug01. The data was taken between 22 and 7 hours AST. The sources were:

30jul01 plots before motor installed (.ps)  (.pdf)
01/09aug01 plots after the motors were installed (.ps).  (.pdf)
These plots show the measured data for each day:

  • Figure 1 is the Zenith angle pointing error in arc seconds versus za (top) and az (bottom).
  • Figure 2 is the Azimuth angle pointing error in arc seconds (great circle) versus za (top) and az (bottom).
  • Figure 3 is the pointing error plotted versus azimuth and zenith angle. The length of the arrow is proportional to the magnitude of the pointing error (1 tick mark equals 5 arc seconds). The direction of the arrow is the direction of the error.
  • Figure 4 shows the beam squint (pointing error polA - pointing error polB). The plots top to bottom are: squint in za direction versus za, squint in az direction versus za, squint in za direction versus az, and squint in az direction versus az.
  • Figure 5 is the gain in Kelvins/Jansky versus za (top) and azimuth (bottom). The fluxes were taken from chris salter's fits. A cal was fired at the beginning of each strip to convert to kelvins. Since each strip lasted up to 2 hours, the electronic gain of the system will vary with temperature. Using a single cal measurement will cause errors in the gain (probably a few percent).
  • Figure 6 is the System Equivalent Flux Density (SEFD) in Janskies per Tsys. It only relies on the source flux so the electronic gain drift will not affect it.
  • Plots of the change in pointing, gain, and sefd (.ps)  (.pdf)
    These plots show the change in the parameters before and after installation.
  • Figure 1 has the change in zenith angle pointing error (Before - after) in arc seconds versus az (top) and za (bottom).
  • Figure 2 has the change in azimuth pointing error (before - after) in arc seconds versus az (top) and za (bottom).
  • Figure 3 is the % change in gain (gainAfter/gainBefore - 1.)*100. Positive numbers mean the gain has gotten better. The gain for a particular strip can vary since there is only 1 cal measurement per strip. This will cause the ratio of strips between days to also vary.
  • Figure 4 is the % change in SEFD (sefdBefore/sefdAfter-1.)*100. Positive numbers mean the performance has gotten better (the sefd decreased). Changes in this value come from the gain or the system temperature.
  • Figure 5 is Tsys versus az (top), za (bottom) for both periods. * is before change, + is after.
  • The tertiary was positioned to +/- 5 arc seconds from before the motors were installed. We positioned the tertiary to the theoretical position rather than the position prior to the motor installation. We did this by:
    1. Establish the dome centerline coordinate system by shooting the secondary.
    2. Position the theodolite to the theoretical position and then move the tertiary till the targets lined up with the theodolite cross hairs.
    The gain was constant to within +/- 2%. This variation could be attributed to the electrical gain variation since we only took 1 cal per strip.
    The sefd ratio had 6% jumps within individual sources. These jumps were also seen in the Tsys measurements but were not as obvious in the gain. Since the SEFD is independent of the cal,  the electrical gain cancels out (Tsrc/Tsys). The jumps were not seen in the gain ratio so these jumps must have been in the system temperature. Jumps in 12 degree dec sources were also seen at cband (02aug01) (.ps) in the gain and the sefd. Correcting for the pitch/roll/focus still left a step (so this is a bit of a mystery).
    processing: x101/010730/doit.pro, x101/010801/doit.pro
    plotting  : x101/010730/doplot.pro, x101/010801/doplot.pro,x101/010801/pltdif.pro