Pointing and Focus optimization

$ : commands to insert in a shell

> : commands to insert in the operatorInput panel

logo: check the execution on the monitor

The pointing and focus optimization requires the Total Power backend. Set first the parameters of the Total Power, then proceed with the pointing and focus procedures described below.

Total Power setup

> chooseBackend=TotalPower logo Fig.21

Insert the bandwidth (300, 730, 1250 or 2000 MHz) and choose the sample rate (in MHz) :

> setSection=0,*,[bw],*,*,[sampleRate],* logo Fig.13

> setSection=1,*,[bw],*,*,[sampleRate],*

Put the antenna at 45 deg of elevation and attenuate the signal in order to have the counts in the range [750-1100] :

> goTo=*,45d logo Fig.15

> getTpi

> setAttenuation=[sect],[att] with [att] the attenuation from 0 to 15 dB. logo Fig.13

Recorder selection and Calibration tool display

The pointing and focus need the calibration tool client and the selection of the correct recorder.

  1. Choose the recorder :

    > chooseRecorder=MANAGEMENT/CalibrationTool

  2. Check if the calibrationtool client is open. If not, open it in a terminal to display the plots in real time :

    $ calibrationtoolclient MANAGEMENT/CalibrationTool logo Fig.27

Pointing

The pointing optimization depends on the elevation of the sources. It is strongly recommended to perform it before observing a source (calibrators and target of your schedules). If the target you plan to observe is too weak to present a good S/N, select a calibrator bright enough and located close to your target (see the internal report N°27.).

  1. Set the azimuth and elevation offsets to 0 degree.

    > azelOffsets=0d,0d

  2. Choose and track a proper calibrator.

    > track=[name] if the calibrator is in the SRT database (e.g. 3c147 => note c in lower case)

    otherwise > sidereal=[name],[RA],[Dec],[epoch],[sector]

    Important note: the complete list of the sources which are recorded in the SRT database is available on the page

    • RA, Dec: Pay attention to the coordinate formats: - decimal degrees, using a d suffix, for any coordinate (e.g. 30.00d) - sexagesimal degrees, with no suffix, for any coordinate (30:00:00) - hh:mm:ss, with a h suffix, for longitudes only (02:00:00h).
    • epoch: 1950, 2000 or -1, the last one meaning that the provided coordinates are precessed to the observing epoch.
    • sector: to force the cable wrap sector, if needed. Its value can be CW, CCW or neutral. Usually, use neutral.

    e.g. > sidereal=3c84,03:19:48.16h,41:30:42.1,2000,neutral or > sidereal=3c84,49.951d,41.512d,2000,neutral

  3. Set proper parameters according to your beamsize and coordinate frame in order to perform a correct pointing measurement :

    > crossScan=HOR,0.5d,00:00:20

    • HOR or EQ frame: use the same coordinate frame as in the .lis of the schedule otherwise the offsets will be rejected.
    • 0.5d indicates the scan length in degrees (in this example 0.5°)
    • 00:00:20 indicates the duration of the scan (in this example: 20 seconds).

    Important note: in the event of not ideal weather conditions, you have to set a smaller scan length value of about 0.15d.

  4. Look at the calibrationtool client to check the pointing offsets.

    Pointing offsets are generally less than 1/10 of the beamsize (i.e. about < 0.005 deg in C-band and < 0.00125 deg in K-band). They can also be slighty larger than these values, in particular in K-band.

  5. If you want to reject the measured offsets :

    > azelOffsets=0d,0d

    and repeat the pointing scan procedure.

Focus

  1. Choose and track a proper calibrator.

    > track=[name] if the calibrator is in the SRT database (e.g. 3c147 => note c in lower case)

    otherwise > sidereal=[name],[RA],[Dec],[epoch],[sector]

    Important note: the complete list of the sources which are recorded in the SRT database is available on the page

    • RA, Dec: Pay attention to the coordinate formats: - decimal degrees, using a d suffix, for any coordinate (e.g. 30.00d) - sexagesimal degrees, with no suffix, for any coordinate (30:00:00) - hh:mm:ss, with a h suffix, for longitudes only (02:00:00h).
    • epoch: 1950, 2000 or -1, the last one meaning that the provided coordinates are precessed to the observing epoch.
    • sector: to force the cable wrap sector, if needed. Its value can be CW, CCW or neutral. Usually, use neutral.

    e.g. > sidereal=3c84,03:19:48.16h,41:30:42.1,2000,neutral or > sidereal=3c84,49.951d,41.512d,2000,neutral

  2. Cancel the previous focus position with:

    > clearServoOffsets

  3. Set proper parameters according to your beamsize :

    > focusScan=150,00:01:00

    The first number should be three times the wavelength of observation in mm (e.g. in C-Band 3*5cm = 150mm). In the case of K-Band observations this value should be set to 60mm.

  4. Look at the calibrationtool client to check the focus measurements. logo Fig.28

    The focus is correct if you see a Gaussian with an offset lower than a few tenth of mm with respect to the zero.

  5. If you want to reject the updated focus position with:

    > clearServoOffsets

    and repeat the focus scan procedure.