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Connecting to the 4m telescope VNC server

  • Connecting from the guest terminal

As the computers in the observer building are connected to the MPIfR internal network, one can simply access the VNC by entering


into a unix terminal and then entering the password. A window should appear with the VNC desktop. This is the telescope control computer "4mteleskop".

  • Connecting from Windows outside the MPIfR network
  • Connecting from Linux outside the MPIfR network
  • Connecting from Mac outside the MPIfR network

Starting the telescope control programs

  1. The clipboard is not shared with the VNC. Thus, it helps if you open the page containing the most important commands through a browser from within the VNC.
  2. Open a terminal on: 4mteleskop
  3. If not already there, go to the directory: /home/operateure/
  4. If you want to specify different folders to save your spectroscopy and continuum data in, you can do so by editing /home/operateure/ through any text editor.
  5. Use the command: ./ This should open all the necessary windows to operate the telescope.
  6. Minimize or resize the windows you don't immediately need so the window with the blue input line is visible. This is from where you can control the telescope.

Preparing the measurement

  • Continuum backend

The continuum backend measures the total flux coming from the telescope over the whole range of Frequencies received. It is usually used to quickly map out where radio sources are. It can be started by entering:

pbebackend('cmdusedchannels 1 1','cmdnumphases 1','cmdmode external','configure')

  • FFTS backend

The Fast Fourier Transformer backend separates the signal from the telescope into its constituent frequencies. This allows the detection of physical processes radiating at distinct frequencies in specific regions of the sky. It can be started by entering:

fitwriter('band1:cmdnumspecchan 8192','band2:cmdnumspecchan 8192','cmdusedsections 1 1','cmdmode int','cmdsynctime 200000','cmdblanktime 2','cmdnumphases 1','configure')

  1. Starting the observation

In both cases the selection of the backend must be followed up by


to actually send the command through the network to the appropriate devices. After this you can start the observation by entering


Observing with the telescope


The telescope can only move within certain limits. These are: 0°-90° Elevation 0°-270° Azimuth Be careful not to let the telescope cross over these limits.


The commands for the telescope have several variables that you change for each command. If you leave out a variable, the control program will use the default value. (Mostly 0.)

Variable Purpose Default Value Unit Other
integration=None, sets the time for collecting radio flux from the specified source None=infinite ms 0 means no data collected
offsetx=(offx,unitoffx), offsety=(offy,unitoffy), sets an offset in az,el to point beside the given coordinates 0, 0, unitoffx and unitoffy in the format 'd' for degrees can be used to fine tune pointing
velaz=None, velel=None, sets the velocity at which the telescope moves along the given axis 'Schleichgang' 'Schleichgang': slow, 'Eilgang': fast, 1: 1°/sec velocity is calculated automatically for crosscans
coorsys = 'J2000.0', specifies in reference to which point in time the coordinates were given 'J2000.0' 'J2000.0' OR 'B1950'
lng = (l, unitl), br = (b, unitb), sets the position of the telescope in galactic coordinates 0, 0, unitl and unitb in the format 'd' for degrees
ra = (rec, unitrec), dec = (decl, unitdec), sets the position of the telescope in equatorial coordinates 0, 0, unitrec and unitdec in the format 'd' for degrees
el = (posel,unitel), az = (posaz,unitaz), sets the position of the telescope in local coordinates 0, 0, unitel and unitaz in the format 'd' for degrees with this option the telescope does not turn with the rotation of the earth
messobjekt, specifies which source to point towards None names looked up in in CDS name resolver
lengthx = (lengthaz,unitlenx), lengthy = (lengthel,unitleny), specifies the distance th telescope should move in az,el during a crossscan 0, 0, unitoffx and unitoffy in the format 'd' for degrees

Observation Commands

  • Point

In order to point the telescope towards a specific heading - for example when shutting it down - you can use the command:

set_position_azel(integration = 0, el = (posel,unitel), offsety = (offy,unitoffy), az = (posaz,unitaz), offsetx = (offx,unitoffx), velaz = None, velel = None)

The correct shutdown position is Elevation: 35, Azimuth: 130,

  • Track

In order to track an object across the sky, you can use the command:

track(messobjekt, integration = None, offsetx = (offx,unitoffx), offsety =(offy,unitoffy))

  • Crosscan

To detect the maximum intensity and precise position of sources, you can use the command:

crossscan(integration,messobjekt = None, az = (posaz,unitaz), el = (posel,unitel), lengthx = (lengthaz,unitlenx), lengthy = (lengthel,unitleny), offsetx = (offx,unitoffx), offsety =(offy,unitoffy))

The speed at which the telescope moves is determined by the integration time given, and the length given for the crossscan. The telescope will move to approximately to "position - 1/2 length" and then sweep over to approximately "position + 1/2 length" over the time frame given. It adds a couple of seconds of movement at the beginning and the end to avoid sudden jolts of the telescope.

  • Calibration

The calibration diode is used to give a reference flux to determine the actual signal strength by comparing the incoming signal to it. For the time being it has to be turned on and off manuall at the start of each scan. This can be done via:




Other commands

  • get_position()
  • get_status()


  • Telescope not moving, not giving out data

This indicates that the telescope control programs froze for some reason and need to be restarted. Close all windows by pressing Ctrl+C or the X button. Restart the telescope control programs via ./

  • Telescope still not moving, optionally giving error messages

If a crossscan was started close to the hardcoded Azimuth endpoints of the telescope, it is possible that the telescope crossed over this endpoint. This means the actuator controls will have to be manually restarted by a technician.

  • Multiple backends online at the same time, don't turn off on restart

This happens occasionally, and while the plotting windows can be a nuisance, the data is unaffected and measurements can continue normally.

  • is not accepting the password

First the validity of the password needs to be checked. If it is still not allowing a connection the wrong password may have been entered too many times, in which case a technician will need to restart the VNC server to reset the lockout.

  • Other Error

If the telescope does not function due to a different error, you should contact a technician.

information_for_astronomers/user_guide/tutorials/4mtelescope.1533561190.txt.gz · Last modified: 2018/08/06 15:13 by cvtoth