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Satellite television antenna must be in direct view of
satellite emitter. This may be difficult to check if nearby
obstacles hide nearly the satellite. This became obvious if the
sun is at the same place as the desired satellite: The dish must
be irradiated by the sun. This is the case twice a year. The moon
may be used more frequently: nearly twice a month.
Azimuthal position of a fixed satellite antenna (elevation/azimuth) can be checked (nearly each day) when the sun azimuth is equal to the satellite azimuth.
Check the satellite position
Use this java applet to find the favorable date. Enter your position, and a satellite as:
|Antenna longitude||0 to 180 degrees||W or E|
|Antenna latitude||0 to 90 degrees||N or S|
|Satellite||0 to 180 degrees||W or E|
And click on " Calculate first date ".The two first
lines of the results give the time at the lowest angular distance
between the sun and the satellite for two successive days for
pass above and under the satellite. The two following lines give
the same data for the moon.
For the sun the step between two days is small: about 0.4 degrees and you can use the following or preceding days.
For the moon the step between two days is large: about 5 degrees so reject the dates with too large errors (the sun or the moon diameter is about a half degree). The last column gives the angular distance between sun and moon in degrees:
|Distances sun-moon||180 degrees||Full moon|
|90 degrees||Half moon|
|low values||Moon is not visible|
This applet may also help you to check the orientation of your dbs dish: It is possible to visualize the parabola focus with the help of small (1 or 2 cm) pieces of mirror fixed to the surface of the antenna. This may be useful if several LNB are added to an antenna. This cannot replace adjustments with the received video signal. The focus verification with the moon is only possible in favorable conditions: at night (when the corresponding sun elevation is lower than -6 or -10 degrees), near full moon, and with low parasitic light
Azimuth 0 to 360 degrees. N 0 or 360., E 90., S 180., W 270. The applet gives the true azimuth. It is possible to use http://www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp to compute the magnetic declination and the magnetic azimuth
Check the antenna azimuth
The lines 5 and 6 of the applet results gives the time when the sun azimuth (or the moon azimuth) is equal to the satellite azimuth: a plumb line shade gives the correct azimuth for your antenna. Do not use this time to check the satellite position: the sun (or the moon) elevation would not be equal to the satellite elevation. For some unusual cases (satellites near the horizon or antenna near the equator) the sun (or the moon) may not reach each day the satellite azimuth and with the button "+ or - 1 day" the date may jump several days (or even months).
Visualize the north south direction (for a rotating polar
Enter a satellite longitude equal to the antenna longitude. The applet gives the time when the sun (or the moon) is south (or north).
Polar angle (for a rotating polar mounted antenna)
The column polar angle gives the angle (degrees E or W) between the meridian plane and a plane defined by the satellite (or the sun or the moon) and the polar axis of the mounting. It is the rotation to be applied to the antenna to receive the satellite (starting from the meridian plane)
Declination (for a rotating polar mounted antenna)
A geostationary satellite is not exactly seen in a direction perpendicular to the polar axis but slightly lower. The angle difference is given in the column declination (+ toward north - toward south). At equator the declination is null
Skew: (Only for vertically or horizontally polarized channels) The vertical polarization plane of a satellite exactly south is also vertical for the antenna. If the received satellite is not south the LNB must be rotated to follow the polarization plane. For a rotating polar-mounted antenna this rotation is intrinsically realized. For a fixed antenna (elevation/azimuth mount) the column "skew" give the rotation (degrees) to be applied to the LNB. Sign + = turn clockwise facing the satellite (northern hemisphere). (+ = counter clockwise for southern latitudes).
The distance between the sun and the satellite is given on the figure (degrees)
Use the stars to check the satellite position
The last line gives the time when the star with a red circle is behind the satellite. The figure gives a map of the stars and the chosen satellite.
An image shows the projection on the celestial sphere (as visible from the antenna position) of the moon, the sun, the chosen satellite, and the satellites geostationary arc. The string "satellites" represents the satellites geostationary arc. It is possible to change the point of view by clicking and dragging the mouse. Try to superpose the W and E points to see when the moon approaches the satellite zone. When you superpose the sphere center and the satellite, the black satellite symbol visualizes the vertical polarization plane . This may help to adjust the skew.
If you want to keep your preferred position in your computer (as cookies) fill this table, click on "store preferred position and satellite as cookies" .
To use this position click on the button in the applet "use
stored preferred manual position"
Try to see in stereo click on " stereo on " Fix a point between the two images far behind the screen. The size may be adjusted to fit your vision.
The times results can be displayed using either of two different methods. The first one use java.util.Date toString() (local) and toGMTString(). The second use java.text.DateFormat with a local or a GMT time zone. The button "util.Date->text.DateFormat" select the displaying method.
Important for Internet Explorer 4 users (including win98
The time given by your java virtual machine may be wrong: Please check this:
There must be no discrepancy between the local time and the GMT time given by the applet: for instance if the local time string is "12h (GMT+02)" the GMT time must be "10h " and not "11h "
Results for the default values (7.2E 43.7N sat 19.2E) sun must be on 10 Oct 10h24 GMT and on 3 Mar 10h49 GMT .(I found error of one hour on GMT in daylight saving time with my original IE4 or win98)
Some details on this anomaly here ..
To suppress the java time anomaly download the last version of the java virtual machine
To display java applets
To display java applets (and the two applets in this page) you must download the java virtual machine at http://java.com.
Satellites info at Lyngemark Satellite Chart.
Jet Propulsion Laboratory gives the sun and moon position (if you want to test the accuracy of the applet).