Some brief explanations
This is a simulator of the software with which the 1.4 GHz antenna
at DL0SHF in the village of Rönne is controlled and operated
to make radioastronomical measurements. The Radiometer version
measures the radio flux in the continuum in a 1.4 MHz wide band
at 1305 MHz. It permits to make realistic 'observations' of sky
objects in the same way and to produce data with the same quality
as the real instrument. Likewise, the amount of noise is similar,
as are the occurrences of radar signals, birds flying
across the antenna lobe, drift of the electronic noise level,
and noise from the antenna motors. It includes the quiet Sun,
the Moon with its monthly variation of surface temperature and
radio flux, a number of bright radio sources, and an idealized model
for the continuum emission of the Milky Way.
The real instrument has these technical data:
- Diameter of the parabolic dish: 9 m
- Effective diameter of the illuminated dish: 7 m
- Effective area of the illuminated dish: 40 m2
- Antenna gain: 40 dBi
- System temperature of the receiving system: 50 K
- Sensitivity: 69 Jy/K or 14.5 mK/Jy
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.
- 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 grove of trees which provide 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 have additional features ...)
The two text fields to its right 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.
- the Plot: shows the received power in terms of decibels (dB)
relative to the level of the receiver noise (represented by the system
temperature Tsys = 50 K for this instrument) 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
- 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.
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) -- this works OK with Chrome, Firefox, and Edge, but on other browsers
one may find that it works only if the window is not scrolled ...
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. The format is identical to that used by the real
software: each datum is composed of time [UTC], azimuth, elevation, power [dB].
When a large number of data are recorded - for a couple of hours, say -
the browser may have problems showing all the data easily. Therefore,
it might be advisible not to make recordings too long.
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