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Calculation of the orientation parameters of a satellite dish. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Antennas. Measurements, adjustment, coordination

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The article proposes an algorithm and a program for calculating the parameters of the elevation and azimuth required to orient the antenna to a geostationary satellite repeater of television programs.

Before installing the antenna, you must select a satellite - the source of the signal, clarify its name and orbital position, select a transmitter with a specific frequency. This information can be found on the Internet, in particular, the author uses the information posted on the site [1].

The ability to calculate the elevation angle and azimuth of the antenna orientation is provided by a number of computer programs, mainly commercial ones, such as Satellite Antenna Alignment, SatHunter, SMW Link, SatMF. But not all programs allow you to calculate the magnetic azimuth, knowing which, you can use such a simple antenna orientation tool as a compass. According to the author, this is one of the easiest ways to install an antenna. But for this it is necessary to know and take into account the local magnetic declination.

Calculations are performed according to the following algorithm:

1 Elevation calculation:

 

where m is the quotient of the radii of the geostationary orbit and the Earth's equator; A - latitude of the place of reception; B is the difference between the longitudes of the receiving place and the sub-satellite point.

This formula gives the value of the geometric elevation angle without taking into account the influence of the Earth's atmosphere. This influence (refraction) is especially strong for small values ​​of the elevation angle.

2. Elevation angle correction for refraction during signal propagation from a satellite In the practice of antenna orientation, it is advisable to take it into account for elevation angles less than 30°:

degrees, the corrected value of the elevation angle.

3. Calculation of the geographical azimuth:

4. Calculation of the magnetic azimuth:

The most difficult is to determine the local magnetic declination. It is known that the geographic and magnetic poles of the Earth do not coincide. The magnetic azimuth of the direction to the geographic north pole is the local magnetic declination. For the entire European part of Russia, the local magnetic declination is positive. You can determine it for a point with specific geographical coordinates, in particular, using the sites [2] and [3]

Based on the foregoing, a program was written in Visual Basic 6.0 to calculate the angle of the installation site and aim the antenna at a specific satellite, as well as to calculate the azimuth of its installation. Also, for the convenience of the user, if it is necessary to clarify the local magnetic declination, the magnetic azimuth of the antenna installation is calculated. The mathematical part, after appropriate revision, was used from the book [4].

Initial data for calculation:

- satellite position in geostationary orbit;
- geographical coordinates of the place of reception;
- local magnetic declination.

The program works like this:

1. Run the executable file of the program Caljnst Ant v1.4-2.exe. The program window shown in the figure appears on the desktop. At the first start of the program, all initial parameters of the calculation are set to zero, and sections of the calculation results are shown in gray font.

Calculation of satellite dish orientation parameters

2. Enter the value of the longitude of the sub-satellite point for a specific satellite (orbital position of the satellite in geostationary orbit).

3. Enter the geographical coordinates of the receiving point (antenna installation site). Coordinates can be determined by the navigator of the GLO-NASS satellite system or another similar one, and in its absence, by a geographical map.

4. If using a compass, you need to know the local magnetic declination. To do this, enable the option to take into account magnetic declination by clicking on the "Take into account magnetic declination" button. Further, when you click on the "Refine" button, the program itself automatically connects via the Internet to the site [2]. transfers to it the coordinates of the place of reception and reads the results of calculations into the corresponding window. To do this, the program uses the functions of the Internet Explorer browser. To control the operation of the program, it is recommended to check the box "Show the process of requesting the magnetic declination". If the program cannot properly interact with the server of the site [2] (for example, if another browser is installed on the computer), then on the site [2] you can manually fill out the form for the Longitude and Latitude values ​​of the receiving place, after which you need to click on the "Compute Declination" button. The site server will calculate the magnetic declination, which is manually transferred to the program window.

5. Press the "Calculate" button, after which the program will calculate the elevation angle and azimuth, the values ​​of which will be displayed in the corresponding windows. For example, the figure shows the program window for calculating the antenna orientation to the Eutelsat W4/W7 satellite (longitude 36°) at the author's place of residence.

The program provides the ability to print the initial data and calculation results on the system printer by clicking the "Print" button, as well as save them to a text file Callnst Ant.txt by clicking the "Save" button. The program creates this file automatically at the first start, and at subsequent starts adds information to its end. The user can view this file in any text editor, such as Notepad, and delete data that is no longer needed.

When restarted, the program displays the previous initial data, which it saves in the Callnst_Ant.ini file. This is very convenient, especially when working in the same area, since its geographic coordinates and magnetic declination only need to be entered once. On subsequent launches of the program, they are automatically displayed in the corresponding windows.

The program contains the help file Call Ant v1.4.2.chm, which can be launched either from the program using the "Help" menu command, or separately from it. This file contains instructions for working with the program and a table of geographical coordinates and magnetic declination values ​​for a number of large cities in Russia.

If the calculated elevation angle is less than zero, then the satellite is not visible from the selected receiving location. This problem is especially pronounced for high latitudes, with the observed part of the geostationary orbit being significantly reduced

In the case when it is difficult to use a compass due to the interfering influence of metal structures, it is possible to determine the direction to the north according to the Sun, as described in article [5].

The operation of the program has been verified for the north latitude and east longitude of the receiving location.

The program can be downloaded from ftp://ftp.radio.ru/pub/2012/05/spant.zip.

Literature

  1. LyngSat - lyngsat.com
  2. NOAA NATIONAL GEOPHYSICAL DATA CENTER.
  3. Magnetic declination calculator.- geomag.nrcan.gc.ca apps mdcal-eng.php
  4. Stevenson D. Satellite TV. Practical guide: Per. from English. - M.: DM K 1 Press, 2001.
  5. Davidenko A. Antenna azimuth indicator on reed switches - Radio, 2008. No. 8 p. 55-57

Author: V. Belyaev

See other articles Section Antennas. Measurements, adjustment, coordination.

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