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An octave script (fitter.m) is available for reducing scans made using “ramps” in the HMI controller and the “monochanstart.sh” scripts in ~oper/Agilentu2k/
. The monochanstart.sh script reads from the power sensor and writes it to a file - usually ~oper/Agilentu2k/sensordata.txt. To use the script, start octave and run fitter
from the command line. You will be prompted for a file name and the mjd day and seconds of the scan. The output is the amplitude (in dB), the FWHM and central location (in seconds). To best use this, scans made using a ramp where the nominal position is reached at a defined epoch are recommended as this allows for simple estimation of the pointing offset (fitter central location - ramp epoch)*(ramp rate in degrees/sec). The script is made up of three files - fitter.m, fittererr.m and julday.m and requires the debian packages octave, octave-io and octave-optim to be installed.
17 Feb 2011
Investigation of the elevation offset problem suggests a physical (encoder) cause.
Brett made an inspection of the elevation encoder mount on Feb 16 afternoon. He found that the bolts attaching the aluminium encoder bracket to the antenna were loose and so he tightened them up a little. We’re inclined to see if this has fixed the problem before attempting to remove the encoder and coupling to check the coupling to encoder shaft join.
A pointing check after this showed a 0.05 deg offset
New data show a mean El offset of 0.155 deg, which appears to be a DC offset. No significal cross-El offset seen.
New P7 = 0.1667 + 0.05 = 0.2167
18 Jan 2011
An offset in Elevation has been detected, which appears to have started between Nov 4 and 8 for no known reason.
New data show a mean El offset of 0.155 deg, which appears to be a DC offset. No significal cross-El offset seen.
New P7 = 0.0117 + 0.155 = 0.1667
3 September 2010
After new feed installation, some additional pointing observations were made. There seems to be a global offset, mostly in Elevation that's constant in all tested Az and El coordinates.
Mean offsets are:
cross El = -0.0033
El = 0.0784
DC offsets in Elevation are in P7 and in cross-El is in P1. So parameters to change are:
P1 = -0.0527 -0.0033 = -0.056
P7 = -0.0637 + 0.0784 = 0.0117
Data used for the new solution
Based on observations from 19 March 2010 and the Version 1 input model. i.e note, this is a re-analysis of data taken for Version 2, but only using the new data. The following offsets were measured: hobart_pointing_v2.0.xlsx. The new solution was calculated using a perl script that uses the same fitting method as used for V2 and V1. Solution is
P1 = -0.05271
P2 = -0.40045
P3 = 0.01455
P4 = 0.00099
P5 = -0.00729
P7 = -0.06368
P8 = 0.01494
P9 = -0.00291
Comparison with previous model:
Stats with V2.0 solution
XEl offsets: Mean = -0.010969, RMS = 0.038104
El offsets: Mean = 0.060875, RMS = 0.056499
Stats with new solution
XEl offsets: Mean = 0.001096, RMS = 0.012678
El offsets: Mean = -0.000078, RMS = 0.007121
Scatter plot of offsets (before vs after):
Based on more observations and used for the fringe-check on day 110. There still appear to be significant residuals but the solutions are OK for fringe-checking.
Things to check:
Solution (based on all observations to date) used was:
P1 = -0.071
P2 = -0.376
P3 = 0.023
P4 = -0.013
P5 = -0.016
P7 = -0.096
P8 = 0.032
P9 = -0.004
Based on 13 individual observations only, so more work is required and testing of this model is needed. The spreadsheet containing observations and model fits is attached: hobart_pointing_v1.0.xlsx Pointing model coefficients used during the pointing observations:
P1 = -0.36
P2 = 0
P3 = 0
P4 = 0.007
P5 = 0.0082
P6 = 0
P7 = -0.1760
P8 = 0
P9 = 0
Components P4 and P5 are the tilt components in Az and El as provided by Patriot. P1 and P5 are cross-el and El DC offsets (guessed by Jim L). Note P6 is not used so it is effectively a 8 component model. Solutions were obtained with P4 and P5 fixed as well as letting all vary. Of the two, the less constrained model gave the better fit and differences between the old and new model were less, so this has been chosen as Version 1.0. Tests will need to be made to confirm the model is effective and to increase the number of samples on the sky. The Solution is:
P1 = -0.495
P2 = 0.030
P3 = 0.220
P4 = -0.025
P5 = -0.036
P6 = 0
P7 = 0.044
P8 = -0.175
P9 = -0.008
Solutions (offsets from model) before and after:
Following a series of observations resulting in 23 offset measurements on 7 & 8 June 2011, a new model was determined. Model used during observations:
P1 = -0.155 P2 = 0.0 P3 = 0.0 P4 = 0.0 P5 = 0.0 P6 = 0.0 P7 = 0.32 P8 = 0.0 P9 = 0.0
New model:
P1 = -0.0436 P2 = -0.2739 P3 = 0.021 P4 = 0.0124 P5 = -0.0184 P6 = 0.0 P7 = 0.3822 P8 = -0.0193 P9 = -0.0015
No change to encoder offsets in the controller.
This model was loaded on June 8 2011
Stats with old solution XEl offsets: Mean = -0.077, RMS = 0.064 El offsets: Mean = 0.045, RMS = 0.02 Stats with new solution XEl offsets: Mean = 0.0004, RMS = 0.007 El offsets: Mean = 0.0008, RMS = 0.016
Observations on June 8. Further offset of 0.0614 added to El. P7 now 0.7365
Observations on May 23:
El offset = 0.19 xEl offset = 0
No correction applied to model.
Observations on May 25, prior to fringe check:
El offset = 0.215 xEl offset = 0
DC offsets in Elevation are in P7. So parameters to change are:
P7 = 0.4601 + 0.215 = 0.6751
Model updated 25 May 2011, 02:12 UT.
Observations on May 16, following work by Brett and Randall on the 13th (see ops log) showed a new DC offset in El no offset in xEl.
El offset = 0.11
DC offsets in Elevation are in P7. So parameters to change are:
P7 = 0.3501 + 0.11 = 0.4601
Model updated 16 May 2011.
Observations on May 3 and 4 showed a new DC offset in El and a small offset in xEl.
El offset = 0.35 xEl offset = -0.025
DC offsets in Elevation are in P7 and in cross-El is in P1. So parameters to change are:
P1 = 0.0007 -0.025 = -0.0243
P7 = 0.0001 + 0.35 = 0.3501
Model updated 5 May 2011.
Following a series of observations resulting in 50 offset measurements, a new model was determined:
P1 = 0.0007 P2 = 0.0036 P3 = 0.0165 P4 = 0.0110 P5 = -0.0074 P6 = 0.0 P7 = 0.0001 P8 = -0.0580 P9 = 00021
No change to encoder offsets in the controller.
This model was loaded on April 11 2011, 03:30 UT.
Stats with old solution XEl offsets: Mean = 0.010638, RMS = 0.009923 El offsets: Mean = -0.068184, RMS = 0.015451 Stats with new solution XEl offsets: Mean = -0.000139, RMS = 0.009912 El offsets: Mean = -0.000236, RMS = 0.014916
Initial pointing offsets (Stas) were xEL=0.24, El=0.4.
April 6:
Changed P1=0.24
P7 still 0.4
All others kept to 0
Also changed site elevation to 200m from 100m
April 7:
Based on limited pointing data and some follow-up checks, the following model was used:
P1 = -0.0058 P2 = 0.0 P3 = 0.0142 P4 = 0.0114 P5 = -0.0081 P6 = 0.0 P7 = 0.05 P8 = -0.0265 P9 = -0.001
As well as this, encoder offsets were loaded into the controller EL module (20.21) and Az master module (20.21) as follows:
El 20.21 = -50067 (i.e. -5.0067 deg) Az 20.21 = -1141 (i.e. -0.1141 deg)