Ham Radio 2000/Ham Radio 2000.iso/ham2000/misc/geost/geost.txt

Text File | 1992-06-01 | 22KB | 389 lines

                GEOST 1.2, Geo-Stationary Satellites' position


                           by Giuliano Artico I3LGP




                               C O N T E N T S

  1. Introduction.
   2. Location setting.
   3. Pilot satellites.
   4. Storage of locations.
   5. Output.
   6. Format of the configuration file.
   7. Options on the DOS command line.
   8. How to determine the QTH locator.
   9. Setting of the antenna system.

                                   ********

   1. Introduction.

   The program GEOST is designed as an aid for the installation of antenna
systems for geo-stationary satellites. All such satellites are placed in a
circular orbit above the equator. Their angular velocity is equated to the
angular velocity of the earth, in order to maintain each of them always above
the same point of the earth surface. Therefore, tracking a determined
geo-stationary satellite is a trivial operation, as any observer sees it as a
motionless object in the sky. However, the problem which arises is that of
installing the antenna system in such a way that it is always directed towards
points lying on the orbit of geo-stationary satellites, when it is rotated in
any direction, since in this way it turns out to be easy to have access to
different satellites (section 9).
   The program GEOST supplies the values of azimuth and elevation for three
"pilot" satellites which are denoted by "Western", "Central" and "Eastern"
respectively (see section 3). One should choose those which are more
appropriate for the given location. The idea is to assume as "Central" the
satellite which is more or less positioned on the same meridian circle as the
site of the user. The "Western" and"Eastern" satellites are the extreme ones in
the West and East directions respectively, among the ones seen by the
observation point or, otherwise, among the ones which the user wants to
receive.
   The program also displays the elevation under which the antenna sees the
culminating point of the geo-stationary orbit: this value is generally equal to
the elevation of the central satellite, if its choice has been made in a
reasonable way.
   The last value provided by GEOST is the difference between the direction of
the meridian of the observer and his azimuth bearing for the central satellite:
this allows an easy calibration of the geographic orientation: in fact, the
compass is not accurate enough for our goals. The difference is computed with
respect to the South direction for the points on the boreal (northern)
hemisphere and with respect to the North direction for the points on the
austral (southern) hemisphere.
   The following data are required as input:
  - the position of the observer;
  - the longitude of the western satellite;
  - the longitude of the central satellite;
  - the longitude of the eastern satellite;
  - some optional data dealing with the output on disk or printer.
Observe that the west longitude and the south latitude are assumed to be
negative numbers.
   For the above data, excluding the observer's position, default values are
assumed if necessary.
   For the position of the observer, two different formats are recognized:
  - the Maiden Head Grid Square notation, referred to as QTH locator (see
    section 8);
  - the geographic latitude and longitude.
Three kinds of output are supported:
  - to the screen: this is useful for interactive operations;
  - to a standard ASCII text file;
  - to a printer.
For the second and third option, two types of format may be selected (see
section 5).
   The software GEOST may be configured by storing permanent data(location of
the receiving station, longitude of pilot satellites, parameters for the
printout) in the file GEOST.DAT: if such file does exist and its format is
valid, then the information contained in it are automatically loaded at the
start up.
   These data may be also entered at the DOS prompt, by using the appropriate
options.
   In the case that an interesting location must be examined again later on, it
is possible to store it by means of the appropriate function key.
   Finally, the list of available commands is always present in the lower part
of the screen, while a help screen is shown by typing the character "?"
(question mark) as argument at the DOS prompt after the name of the executable
file GEOST.EXE.

   2. Location setting.

   The position of the receiving station may be entered in two different
formats: the so called "QTH locator" and the geographic latitude and longitude.
The user may adopt the whichever he prefers.
   Three different ways of entering the QTH locator are available:
 1) by editing the suitable line in the configuration file GEOST.DAT (this
    information will be loaded any time the program is run);
 2) with the option /Q at the DOS prompt (the option /Q has priority with
    respect to the locator stored in the configuration file);
 3) within the program, by pressing the Q key. In this case, a further
    stroke of the Enter key produces the request for the observer's
    latitude and longitude.
(Notice that the geographic co-ordinates may be entered only in the last way).
Whenever the location is entered, the program calculates and displays the
following information:
  - the location in both formats;
  - azimuth and elevation for the three pilot satellites (each in a
    different line);
  - the maximum elevation of the antenna;
  - the correction for reaching the direction of the meridian plane
    starting at the direction of the central satellite;
At this point the location may be adjusted interactively by pressing either the
arrow keys for a small shift or the N, W, S, E keys for a big shift in any
direction. The updated information is displayed at once: in this way one can
reach the desired position through successive adjustments.
   A validation check is made on input data: if some error is detected, then
the program prompts for a new input.
   It should be noticed that the QTH locator is less accurate than geographic
co-ordinates: therefore, when the location is defined through the first
notation, an average value is computed for longitude and latitude and a
round-off error may occur.
   About the /Q option and the format of the configuration file, see below.

   3. Pilot satellites.

   The program GEOST provides the azimuth and elevation for three satellites
chosen by the user with regard to his particular situation. This feature allows
the highest accuracy since it facilitates detection of any difference between
computed and measured values, by comparing results for the three objects.
   The longitude of each satellite may be input either by editing the
appropriate line in the configuration file or supplying one of the options/W,
/C and /E as parameters on the DOS command line for the western, central and
eastern satellites respectively. The range of longitude for pilot satellites is
from -180 to 180 degrees and is a decimal number. Notice that West longitudes
must be preceded by the sign "-" since they are negative numbers.
   The information about pilot satellites is displayed in a line at the centre
of the screen: the function keys from F1 to F6, pressed together with the Alt
key, may be used to modify these values during the execution, in steps of a
tenth of degree. More precisely,Alt-F1 and Alt-F2 decrease and increase the
longitude of the western satellite; similarly, Alt-F3 and Alt-F4 act on the
central satellite, Alt-F5 and Alt-F6 act on the eastern one.
   If no value is entered for one or more pilot satellites(either by means of
the configuration file or with the external options) then the following default
values are assumed for the missing ones:
   Western = -27.5
   Central = 13.0
   Eastern = 23.5
In any case, notice that these default are defined just as an example: the
configuration file or the external parameters (with a batch file) should always
be used.

   4. Storage of locations.

   It is possible to register permanently on disk some locations which may be
useful in the future.
   The list of stored locations is present at any time on the screen and any of
them may be retrieved simply by pressing the corresponding function key (from
F1 to F10). When the location is loaded, the related calculation is performed
and the new information appear on the screen. From that moment onwards, that
location is the one to which the arrows and N, W, S, E keys apply.
   Conversely, to store the location present on the screen, just press the
appropriate function key together with the Ctrl key.
   Look at the list of stored locations to choose an empty record. In any case,
to overwrite an existing location it is enough to press the corresponding key
combination twice. This procedure guards against the accidental loss of data.
   Finally, observe that the location storage is made by geographic
co-ordinates, which are more accurate than the QTH locator.

   5. Output.

   The results of the calculation made by GEOST are presented on the screen or
may be sent to a printer connected to the parallel port LPT1 or to a file named
GEOST.LOG.
   The data displayed on the screen in any moment are relative to a single
location and may be changed interactively. On the contrary, the information for
the printer or for the log file consist of the values for two possible sets of
locations:
  - the stored locations, discussed in the section 4;
  - the locations contained in a region centered on the location displayed
    on the screen.
To register the data relative to these sets in the log file, one must press the
F key. Similarly to send the output to the printer one has to use the P key.
After pressing one of these keys, the program prompts for the desired set of
locations.
    In the log file or printer output, the values relative to every location
are contained in a separate line. Explanatory headings are put at the top of
every column.
   Due to the second option, the region for which data are computed turns out
to be defined by three parameters which may be entered either through the
configuration file (see section 6) or with suitable options at the DOS prompt.
   The distance between the points of the grid, into which the above mentioned
region is subdivided, is called "Increment" and corresponds to the external
option /I.  The unit of measure is minutes of angle.  Within the program,this
parameter may be adjusted with the "I" key, in steps of 5 minutes, in the range
from 5 to 60 minutes.
   The region can be thought of as a big rectangle whose horizontal size (in
the longitude sense) and vertical size (in the latitude sense) are defined by
the options /H and /V respectively. The unit of measure for these parameters is
the increment amount described above and they may range independently from 1 to
21. These parameters may be changed with the "H" and "V" keys respectively.
   The default values for the above parameters are 15 minutes for the
increment, 9 and 5 for the horizontal and vertical size respectively.
   The region is scanned row by row from North to South and the locations in
every row are listed going from West into East. The character "*" (asterisk)
identifies the first location in every row.
   The total number of locations contained in the defined region is displayed
on the screen and this value supplies an estimation of the number of pages
which would be printed.
   The size in lines of a printed page is defined by the option/L on the DOS
command line or via the configuration file. Within the program, this parameter
can be adjusted with the Alt-F7 and Alt-F8 key combinations.
   The values for horizontal and vertical size are odd numbers and the program
rounds any value for these parameters to the smallest odd number greater than
or equal to the given one.
   When output data are written to the log file, the previously existing data
are not deleted because the new ones are appended at the end of the file. The
operation may be successful only in the case that the first line of the file
contains the validation sentence "GEOST.LOG - Output file": if the file does
not exist, then a new one is generated with the correct heading.
   Notice that if the printer is connected to a port other than LPT1, then the
output must be re-directed to it before running GEOST by means of the DOS
command MODE. For instance, if the port is COM2, use the following command:
C:\>mode lpt1=com2

   6. Format of the configuration file.

   The configuration file allows the personalization of the program GEOST, so
that any user may start the program with the desired values for all parameters.
   The configuration file is a standard ASCII text file which may be edited
with any text editor or word processor. The program GEOST recognizes this file
as valid only if the first line contains the sentence
                       "GEOST.DAT - Configuration file".
   If a line contains a character "#", all the part of that line to the right
of this character is skipped, so that any line may include a comment.
   Every parameter is associated to a key-word which must be put at the
beginning of a line and followed by the corresponding value.
   Parameters should be supplied as in the next example:

GEOST.DAT - Configuration file
QTH-Locator= JN65DR   #Observer's QTH Locator
WesternSat = -27.5    #East longitude of the western satellite
CentralSat = 13.0     #East longitude of the central satellite
EasternSat = 23.5     #East longitude of the eastern satellite
Increment  = 15 #Distance between the locations to be printed
Horizontal = 9  #Horizontal size of the region
Vertical   = 5  #Vertical size of the region
PageLength = 63 #Length of the printed page

   7. Options on the DOS command line.

   All the parameters contained in the configuration file may also be supplied
to GEOST by means of suitable options on the DOS command line when the program
is run.
   Any option consists of a slash "/" followed by a letter: the value of the
associated parameter must be typed immediately to the right of this letter. For
example, to enter the QTH locator JN65HQ, use the option /Qjn65hq(case
insensitive).
   The list of valid options is shown when a "?" character appears as argument
on the DOS command line.
   Valid options are:
  /Qxxxxxx    Observer's QTH Locator
  /W[-]nnn.n  East longitude of the western satellite
  /C[-]nnn.n  East longitude of the central satellite
  /E[-]nnn.n  East longitude of the eastern satellite
  /Inn        Increment, the grid width for the region printout
  /Hnn        Number of locations of the region in the longitude sense
  /Vnn        Number of locations of the region in the latitude sense
  /Lnnn       Printed page length (in lines)

   On the command line one or more options may be entered in any order: if an
option appears twice, then only the first occurrence is assumed.
   Example:  C:\>geost /qio92og/w-31.35 /p60 /i30
sets the location to IO92OG, the longitude of western satellite to 31.35
degrees west, the number of lines per printed page to 60 and the distance
between points of the printout grid to 30 minutes.

   8. How to determine the QTH locator.

   The Maiden Head Grid Square notation or "QTH locator" is well-known to
Amateur Radio Operators. The QTH locator is an abbreviation for the geographic
co-ordinates and it is very useful since, due to its concision, it may be used
to designate quickly any point on the earth's surface, with a satisfactory
accuracy for most purposes.
   The algorithm for determining the QTH locator when the geographic
co-ordinates are given is sketched below. In any case, this calculation is
automatically performed by GEOST, so that this section may be skipped.
   The QTH locator consists of six characters, subdivided into three groups:
two letters from A to R, two figures from 0 to 9 and two letters from A to X.
The first character in any group is related to the longitude, the second one to
the latitude.
   First group: 18 characters are available from A to R, so that 360 degrees of
longitude from -180 to +180 degrees are divided into portions of 20 degrees,
while 180 degrees of latitude from -90 to +90 degrees are divided into portions
of 10 degrees. In this way we have 18*18=324 large pieces of the earth surface.
   Second group: each of the above pieces is subdivided into 10 parts along
both dimensions, so that it contains 100 "squares", with the size of 2 degrees
and 1 degree for the longitude and for the latitude respectively.
   Third group: 24 characters from A to X are used to denote 24*24=576 spots in
any square. The longitudinal (horizontal) size of every spot is 120/24=5
minutes, while its latitudinal (vertical) size is 60/24=2.5 minutes.
   The directions into which the angles are measured go from West to East for
the longitude, starting at the -180th meridian, and from South to North for the
latitude, starting at the -90th parallel (South Pole).
   For instance, suppose we want to calculate the QTH locator for the following
location:
   Longitude:  11 degrees   38 minutes  40 seconds East
   Latitude :  45 degrees   41 minutes   5 seconds North
In view of the last remark, these values are translated as follows:
   Longitude: 11+180=191  38  40
   Latitude : 45+ 90=135  41   5
We begin calculating the first character of the three groups, by using the
longitude value.
   First group:
the integer part of the quotient 191/20 is 9, so we take the 10th letter J.
   Second group:
the remainder of the above quotient is 11. Since the squares have a horizontal
size of 2 degrees, we take the integer part of the quotient 11/2 which is 5.
   Third group:
the remainder of the above quotient is 1. We reduce it to minutes and add the
portion of degree given by minutes and seconds:
   60 + 38 + 40/60 = 98.7
Since every spot has an horizontal size of 5 minutes, we must take the letter
T, which is the 20th one: in fact, 98.7/5=19.7.
   A similar calculation must be made to determine the second character of the
three groups, by operating on the given latitude. We need only use the vertical
sizes of the various portions, which now are 10 degrees, 1 degree and 2.5
minutes respectively.
   First group :  135/10        13   N
   Second group:  135 - 13*10    5   5
   Third group :  41.1          16.4 Q
Therefore the QTH locator we are looking for is JN55TQ.
   One may also perform the converse calculation to determine the geographic
co-ordinates, if the QTH locator is known. Obviously, in this case a rounding
error may occur.
   Notice that the QTH locator cannot be computed for the two poles, since for
such points the geographic longitude is not defined.

   9. Setting of the antenna system.

   To install an antenna system for geo-stationary satellites, it is necessary
to set the following once and for all:
 -  the antenna rotation axis must be parallel to the earth rotation axis;
 -  the elevation must be fixed at the proper value.
When this is done correctly, the antenna may be rotated on its axis and it
always "sees" points of the geo-stationary orbit, which is a circle concentric
with the equator and with a radius of 42234 Km.
   Observe that the peak position of the system along its rotation should
result exactly when the antenna is beaming into a direction parallel with the
plane of the meridian circle.
   To obtain this, the following steps are to be performed, by using
appropriate measuring devices (compass, goniometer):
  - ensure that the basis is perfectly horizontal;
  - with the help of a compass, point the system South: this direction will
    be corrected later on;
  - settle the antenna axis with an inclination equal to the latitude, with
    respect to the horizontal plan: this setting must be as accurate as
    possible and should not be modified in the following;
  - by rotating the system on its axis, bring it to the peak position;
  - look for the strongest signal of the central satellite, by rotating
    only the system base and adjusting the elevation (in this step the
    antenna should not be rotated on its axis);
  - if the resulting azimuth does not coincide with the one provided by
    GEOST, it is necessary to make an adjustment, by rotating only the base
    of the system, for an amount equal to the value called "correction".
The last alignment is due to the deviation of the magnetic South with respect
to the geographic South.
   If the real elevation and the one given by GEOST coincide, then this is the
final position of the system. A little difference occurs, hence a little
correction of the elevation is needed, when the central satellite's longitude
disagrees too much with the observer's longitude.
   If the divergence is too large, then the process is to be repeated with
higher accuracy. A further verification can be done by comparing the values for
the western and eastern satellites.

                                   ********

   GEOST includes the following files:
GEOST.EXE   executable file;
GEOST.TXT   documentation file;
GEOST.DAT   example of configuration file (ASCII text file);
GEOST.SAT   example of file for the storage of locators;
GEOST.LOG   file for data logging;
GEOST.BAS   source code.

Address: Dipartimento di Matematica Pura e Applicata
       : Via Belzoni 7, 35131 Padova, Italy
Phone  : [phone]
E-mail : Internet = [e-mail]    Decnet = 38999::ARTICO