30may16: Alfa calibration scans, rotation
Compare to may14 results after
Compare to may15 results after
Alfa was reinstalled in the dome on
13may16 after being worked on in the lab. Spider scans (heiles
scans) were taken with alfa on 30may16 using beams0..6
This data was taken with model18A and with the tiedowns
- The alfa rotation angle was set to 0 degrees.
- The wapps took data with 100 MHz bw centered at 1440 MHz. The
100 MHz rf filter were used .
- The program cycled through the various beams. Beam 0 was
sampled more often than the others to get a better measure of
the pointing offsets.
Calibration run results:
The plots show the
calibration results (.ps) (.pdf):
- I removed 2 patterns where the tiedowns had lost tension.
- Page 1: the az/za coverage. Colors specify the beam that was
- Page 2: gain,Tsys,SEFD, avgBeam width. This used the standard
cal values. Colors show the different beams
- Page 3: coma, 1st side lobe height, beam efficiency (main
beam) and (main beam + first side lobe).
- Page 4: Pointing error (all beams)
- Page 5: Pointing error (beam0).
- beam0 mean offsets will increase the rms of all beams.
Fitting for rotation angle error:
Part of the pointing error could come from the
alfa rotation angle being off. To test for this :
Plots showing the pointing error vs rotation
angle offset (.ps) (.pdf):
- Compute the change in the pointing error if the alfa rotation
error was off by -5 to +5 degrees in .1 degree steps. Do this
for each beam separately.
- For each of the .1 degree steps recompute what the pointing
error would have been for each measured position.
- Plot the rms error and mean error for these newly computed
series. Do this separately for beam 0 (which is not affected by
rotation) and the other beams.
- Top: rms pointing error vs rotation angle offset.
- For each offset (-5 to .5 in .1 degree steps) the rms
pointing error was recomputed
- + beam 0, * beams 1,2,3,4,5,6
- Black is the
total rms (rmsAz, rmsZa added in quadrature)
- Red: Az rms pointing
- Green: Za rms pointing
- The total rms minimizes at a rotation offset of 1.3 degrees.
It is about 3 asecs less than the value with no rotation
offset (what is currently being used).
- Bottom: mean pointing error vs rotation angle offset
- Black tot Mean error. az and za added in quadrature.
- green: mean za error,
- red : mean az error.
- We probably need to redo with the beam0 offsets removed.
- There aren't as many points as the may15 run so differences
may be from the smaller numbers.
- The gain,sefd, cals look ok
- Tsys for beam 0 is a little higher then may15 (31 vs 29k)
- sefd for beam 0 is also a little higher than may15.. so it
is probably a true change in Tsys and not a cal problem.
- sefd is : beam0:2.8 jy , outer beams about 3.4Jy (this is a
bit higher than may14..)
- pointing errors:
- rotating by + 1.3 degrees reduces the non beam 0 rms from 13
to 9 asecs.
- in may15,may14 we got 1.1 deg rotation correction. The
difference is probably the small number of measurements made
- Pointing Notes:
- we only did 58 measurements (all beams included).
- there was not an even distribution of north, south sources.
- The pointing errors look similar to the last 2 measurements