The satellites are out tonight; setting up a private ground station. Donald F. Biresch.
Millions of people use cable TV to watch films, cultural events, professional sports, and distant television stations. For most of us, one or two pay services, a Superstation, and maybe MTV is about as exotic as we'll ever get. A few people are using private ground stations to receive the same services in addition to signals from other sources, sent through geosynchronous satellites. They are called geosynchronous because they revolve at the same rate as the Earth, appearing to stay in one location. Lock onto one satellite and the signals are available for your viewing.
What extras can you pick up? Some network programs are fed to affiliates earlier than the scheduled airtime. News organizations use satellite communications to transmit and receive news reports from distant locations, so it is possible to pick up a late-breaking news story before airtime. Suppose your favorite football team blacks out home games; with a satellite dish, you can watch the game. The legal aspects of tuning into signals are unclear, and viewing for private, home use is thought to be safe, but check current FCC regulations regarding the iunterception of private signals to be sure.
Satellite dishes and the connecting equipment are expensive, with costs running in the thousands of dollars. After installing a satellite dish, connecting it to decoders and tuning equipment, you must find out where the satellites are. This is often the most difficult part of hooking up with a "bird."
Guides as to the general location of satellites are available, but they give only a general idea of the location of a given satellite. What you need is a way of personalizing the search for the area where you live. Since the values used are constant--azimuth and elevation angles for the satellites, and the location of the receiving station--alll you need to do is make the correct calculations. Why not use your computer to help you? Just enter the proper values, and the correct location of a satellite will be shown. The Gesosynchronous Satellite Locator Program
Geosynchronous Satellite Locator was written for an Atari 800 with one disk drive, Atari Basic, and an optional Epson printer.
The program automatically computes azimuth and elevation angles for geosynchronous satellites. The program will work for any geosynchronous bird as long as its longitude and height above its subpoint are known. Using The Program
All necessary data except the earth station coordinates are included in the program for the satellites currently in orbit in the Clark Belt. The program automatically compensates for the hemisphere in which the earth station is located.
All input is via the keyboard. All angular data are requested in degrees. However, it would be a trivial task to allow input in radians. Distances have been (at the user's option) permitted in miles or kilometers.
Although the program provides for hardcopy, this feature is user selectable at run time. Therefore, a printer is not necessary to use the program.
The program is self prompting, and since it is written in Basic, it is pretty well self documented. The equations used in the program can be found in most books on advanced trigonometry.
A sample printout for my location is included as an example. Both kilometers and miles are demonstrated.
Please note that the geosynchronous satellites are a very special and very simplified subset of the satellite community. This program will not work for orbiting satellites (such as oscar), since these require a moving antenna to maintain contact. The equations for such satellites are considerably more complicated, and their solutions are of little consequence to the average homeowner.
I created this program to simplify the task of establishing a site for my earth station dish.
In using the data derived from this program, it it important to remember that all azimuth angles are true (not magnetic) north. Consult an aviation sectional ch art to determine the variation for your area. Westerly magnetic variation is added, and easterly variation is substracted. If in doubt, any pilot will be able to provide guidance. Generally, here on the East Coast we add westerly location.
With this program, a good quality compass, and an inclinometer (or better yet, a transit), you can accurately determine your window to the Clark Belt satellites. Accurate determination is now even more important since the FCC has approved 2 degree spacing for the geostationary satellites in this belt. Those with 10' or smaller dishes may notice rather severe interference as this new close spacing takes effect. Changes For Other Computers
Since Atari Basic is a subset of most more comprehensive interpreters, the program should be easily adaptable to most home computers. If the trig and inverse trig functions are not available on your machines, series expansions work quite well for the acrccos, arctan, and arccot functions. However, they will slow down execution time considerably.
I have refrained from using the extensive graphics capabilities of the Atari, since these functions would not easily transfer to other micros. The special printer codes used throughout are specifically for the Epson MX80-FT. They will, no doubt, have to be modified for other machines.
For certain satellites an error message may be generated to indicate that the bird is not visible from the earth station. In general, for great circle angles between the ground station and the satellite subpoint (the point on the earth directly below the satellite) which are greater in absolute value than 81.3 degrees the satellite will not be visible.