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Satellite Finder Online (JavaScript)

Current Version: 1.1 (09/10/2012)

All Content © Copyright 2012, P. LutusMessage Page

The Purpose |  The Application |  The Details

(double-click any word to see its definition)

 
The Purpose

"Satellite Finder Online (JavaScript)" (hereafter SFJ) is a Web-based version of my popular Java application "Satellite Finder". This service provides coordinates to help you locate geostationary satellites, primarily for those installing and pointing satellite dishes. If you are a professional dish installer and you expect to be in the field at the time you need pointing information, you may want to download "Satellite Finder" as well (both services are free).

To use SFJ, in most cases you don't really need to enter any information — the program will use network resources to approximate your location, print a map and set the program's geographical location entry fields. For satellite dish alignment, this approximate position is nearly always more than adequate.

To enter a custom position, for example to create a satellite pointing table for a location other than your own, either zoom and click the map, or type in a geographic position and click "Compute".

There is more complete documentation below the application.

The Application

Use a network-derived approximate location: 

Awaiting network location ...

(your browser may ask your permission
to provide this information)

Or type in a position:

Name Degrees Minutes Hemisphere
Latitude
North South
Longitude
West East
Magnetic declination  

Here are the results (full explanation below):

The Details

NOTE: Because of an abandoned Google service, this page suffered a geolocation outage of several months' duration. It is now (August 2012) fully restored, and should automatically locate most visitors once again.

SFJ solves a problem becoming more important as we become more reliant on satellite communications. Basically, there is now a ring of very expensive jewels circling the earth in a special orbit. Science-fiction writer Arthur C. Clarke first had the idea that a particular altitude would cause a satellite to appear motionless to the revolving earth below. That orbital height, about 22,300 miles, perfectly balances a satellite's orbital velocity with the earth's rotational velocity. This means we can install satellite dishes that point to particular locations in the sky, and the satellites won't drift out of view.

Because all the satellites lie directly over the equator, and because they are all at the same altitude, the mathematics required to produce viewing angles is relatively simple. In fact, the challenges in the design of this page lay more in the area of designing an automated way to locate your computer and printing an orientation map, than in computing satellite pointing angles.

Remember these rules:

  • If you elect to enter a geographical position, remember the entries can be expressed in decimal degrees, or degrees and decimal minutes, as shown in these example entries for 40° 12.5' north:

    • 40 degrees, 12.5 minutes
    • 40.20833 degrees, 0 minutes

    If you choose to make a single decimal degree entry as in the second example above, be sure the minute value is set to zero.

  • Turning now to the data table, the columns are:

    • "Sat Name": The common name of a particular satellite.
    • "Sat Lng": The geographical longitude of the satellite, its position along the geostationary orbit in Earth-centered coordinates. Specifically, a satellite with a listed orbital longitude of -120° would lie directly above Earth's equator at a terrestrial longitude of 120° West.
    • "Az(t)": The true-North azimuthal angle for the satellite at the chosen site. The Azimuth represents a horizontal circle measured in degrees:

      • 0° = North
      • 90° = East
      • 180° = South
      • 270° = West

    • "Az(m)": As above, but for a magnetic North reference rather than True. This number is more useful for a typical field installation where the simplest way to measure azimuth is with a magnetic compass.
    • "El": An elevation angle in degrees, with 0° = horizontal and 90° = vertical. Some satellites will be listed with negative elevation numbers — these represent positions below the local horizon.
    • "Skew:0": This specialized value is only useful for receiver dishes that pick up more than one satellite. These dishes must be rotated around their aiming axis (skewed) to accommodate the relationship between local horizontal and the relative tilt of the geostationary orbit at the chosen location. By convention, a zero skew angle means the dish is level with the horizon, while negative values mean the dish is rotated counterclockwise as viewed from the rear.
    • "Skew:90": This is the same information as "Skew:0" but with 90 degrees added. This is for receiver dish models that have skew scales centered on 90 degrees instead of zero.

  • SFO computes magnetic declination using a special method that is quite accurate, more accurate than needed for satellite dish pointing. Remember when using a magnetic compass in the field that virtually all present dishes are fully or partly ferrous and will spoil the compass reading unless the compass is well removed from the dish itself.
  • The satellite list includes common receiver dish models as well as satellites. These entries produces pointing angles for the most common DiskNetwork and DireTV models.
  • If there are other similar dishes that require special pointing angles, or if there are satellites in common television service that are not in the list above, I would appreciate hearing from interested readers with this kind of information — post to my message page.
  • For readers who need a customized satellite list, I recommend Satellite Finder, my free Java version of this program. It has a plain-text satellite list that is easy to edit for special purposes.
  • For those with Android devices, be sure to check out my Android-based satellite finder — of all the many versions of this program, SatFinderAndroid is the easiest to use in the field and produces the best results, because it acts as a sightning device as welll as a position computer.
 

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