KURT = Kiel's Universal Radio Telescope
Joachim Köppen Kiel Dec.2023


Some brief explanations

This is a simulator of a radio telescope which can work as a single full paraboloid dish or as an interferometer composed of a number of dishes arranged in East-West direction. It can work on any frequency between 100 MHz and 350 GHz. The antenna diameter can be chosen to be any value, but it needs to be larger than 10 wavelengths to behave in a physically correct way. It should also be not much larger than about 1000 wavelength, as then main beam would be narrower than the precision of the position system of 0.01°. As an interferometer, it is supposed to be a local instrument with maximum baselines of a few 100 wavelengths, as the curvature and the size of the Earth are not taken into account.

The characteristics of its receiving system and its positioning system represent the current technology which is freely available rather than involving entail a special and costly development effort. It does not try to model the present limits in sensitivity or resolution of major professional instruments, but it could be found with an amateur installation and thus would be quite imaginable for any small or medium-sized astronomy institute. But as the antenna(s) may be given properties that are mechanically not realisable, one can do things that are impossible to do in reality.

The simulated sky is populated with a realistic but quiet Sun (no solar activity!), a realistic Moon, several major radio sources, a few imagined sources, and a background radiation from the Milky Way and the remnant of the Big Bang. The influence of the Earth atmosphere is modeled by its frequency-dependent absorption and thermal emission, as well as some variability due to local weather. Variations of the noise from the receiving system and from terrestial events may occur in a realistic way, as had been experienced using real instruments at various frequencies.

When not running and operating, the 'instrument' may be used to inspect the sky at different times, and to see the received level from sources, e.g. in preparation for planned measurements.

For further explanations look at the pages Single Dish and Interferometer which describe these operational modes in more detail and show result examples.



Access to the simulator is organized in three pages: Operate, Skyview, and Output. Here is a description of the controls:

Operate: this is the main page, from which all operations are effected, and where all information are displayed.

Before we start observing, we need to select the telescope type and specify some technical data:
The type of the instrument can be:
  • Single dish: an antenna with a paraboloidal reflector. Give the frequency and the diameter of the reflector.
  • E-W adding interferometer with 2 antennas: Give the frequency and the diameter of the single dish, and the separation between the antennas.
  • 2-element E-W correlating interferometer: Give the frequency and the diameter of the dishes, and the separation between the antennas.
    There are two options:
    == correlator cosine output shows the fringes from the real part of the complex visibility.
    == visibility as a function of time, e.g. during a drift scan.
    Also, the current visibility amplitude is plotted in a second graph. Measurements taken at various baselines can be collected. Later, the resulting visibility curve can be displayed and outputted as a table. The maximum baseline for the plot may be entered.
  • E-W interferometer with N-baselines: This correlating instrument consists of the specified number (a power of 2) of antennas which are placed along an E-W line in such a way that the separations between the antennas cover the interval between 0 and the specified maximum separation evenly. Give the frequency and the diameter of the individual dishes.
The second step is to enter the meteorological data of the current weather. This will influence the frequency-dependent absorption of the Earth atmosphere. You may use data from a local weather station, or simply make a reasonable guess. The condition of the sky describes how many clouds are in the sky, which will also affect the atmospheric absorption. Make a rough guess! Having done all that, we may start operations - please note that the technical data (in green fields) of the chosen telescope cannot be altered during operations.
  • Startup: click this to start the operations. If everything starts up properly, the clock will show the current time in UT, and the local sidereal time LST. Also, now all controls can be operated.
    A second click will stop the operations -- however, this would make real sense only with the real instrument, of course.
  • goto Calibrator: clicking this lets the antenna go to the flux calibrator, which is a nearby large building which provides thermal radiation at ambient temperature, like the ground. Thus we look at a source of well-known temperature - about 290 K.
  • goto Park: this lets the antenna go to its parking position.
  • Sun now: a click will display the current position of the Sun in the sky in the fields to the left of the Goto button. Note that this will not move the antenna. If the Sun is below the horizon, the text fields will show a yellow background.
  • Moon now: displays the current position of the Moon. Again, this does not move the antenna.
  • Sun ...: from this list of sky objects one may choose an object, whose present position in the sky is displayed.
  • now: one may choose to pick the object's position at the current moment ("now") or at some later time (e.g. " in 10 min").
  • Go & Track: clicking this commands the antenna to go to the position displayed (left of Goto button), and to track it on its way across the sky. When tracking, this button's text is blue.
    Clicking on it again stops the tracking, and the antenna halts at the last position.
  • current Position: displays the sky position (azimuth, elevation) where the antenna is now pointing at.
  • AzEl: (this button will eventually have additional features ...)
    The two text fields to its right side are used to display the present position of the sky object selected as above, but the user can also enter the position (azimuth, elevation) to which the antenna should go.
  • Goto: clicking this button lets the antenna move to the position given in the text fields to the left.
  • Offs Hor. Vert.: the user may enter any offsets to the current position. Enter your values and hit the 'Enter' key of your keyboard.
    Note that the offsets are in real angles, so that the horizontal offset is Δh = Δa * cos(e) differs from the offset in azimuth!
  • Record: click on this button starts recording all measurements as text on the Output page. Another click will stop recording. Recording data is only possible when the program works in the current time (Now). Note that the Output page starts afresh when the next recording is started.
  • Single measurement: executes a single measurement.
  • Subtract background: in the N-baseline interferometers one may subtract the sky background, which is useful in particular for weak sources.
  • the Plot: usually shows the received power in terms of decibels (dB) relative to the level of the receiver noise or as a function of time.
    Passing the mouse over the plot area will display the time and power at the mouse position.
    The curve is grey when one is not recording, but red when data are recorded
  • Visibility Plot: when recording in interferometer mode, a second plot is shown for the visibility amplitude as a function of the projected baseline.
    Passing the mouse over the plot area will display the relevant data at the mouse position.
    The Reset button permits to clear the plot and reset the table of collected visibilities.
    The log Visi button displays the visibilities in logarithmic or linear fashion.
  • Ymax, Ymin: enter the desired value(s) and hit the 'Enter' key. The plot is refreshed to show it with the new plot limits.
  • Xspan: choose the desired time span to be shown. The plot will always start with the time when the simulator was started or - when small time spans are chosen - at an even number of span intervals later. The simulator has a memory for about one hour.
  • Set: applies the above changes in the plot limits to the plot.

Skyview: shows the situation in the sky above the antenna. The grey area near the horizon shows the ground, two antenna masts, and the small grove of trees in the south-west which serves as the flux calibrator.
Sun and Moon are indicated as yellow and cyan disks, other celestial sources are shown as red dots with their name. The blue curve across the sky is the mid-plane of the Milky Way, with galactic longitudes of 90 and 180° marked as blue circles, and the Galactic centre as a blue dot. A dotted grey curve marks the celestial equator.
When the simulator has been started up, this plot is updated in real time.

  • Now: click this to show current situation.
  • time - 1 hr: click this to show the situation one hour earlier ...
  • time + 1 hr: ... or later
  • Position: a mouse click on the plot then shows the position (azimuth, elevation)

Output: when data are recorded, they are displayed on this page. From here they may be copied and pasted into a text file for further interpretation. First comes a header of comment lines (starting with *) which provide all the technical information of the instrument with which the data are taken. The format of the measurement data is described in a comment line, after which the data lines follow.


| Top of the Page | JavaScript Index | Astropraktikum: Radioastronomie | my HomePage |