How the Astra System Works

You can see them in any suburban or metropolitan environ; tiny dish shaped growths sprouting from walls, roofs and chimneys like high tech fungi, each pointing to a special spot in the sky. They are satellite dishes, the modern replacement to the ubiquitous TV aerials, and the spot they are pointing at if you are in the UK is 28.2°East in the Clarke Belt, a special segment of the space around our planet set aside for communications satellites.

This particular position is inhabited by several satellites called the Astra group, tasked with providing the populace of the UK and Ireland with digital TV programming and streaming.

While it does provide some services to parts of Africa and the Middle East, its main job is making sure that Britain gets their football games and the finals of the Great British Baking Show.

How a Satellite System Works:

There are two main parts of this kind of system:

  • A transmitter:Located in a satellite or satellites. In this case, the Astra group is stationed in a geostationary orbit suitable for covering the British TV market.
  • A Receiver: In this case, thousands of satellite dishes of varying size, each connected to a converter box which in turn connects to a TV monitor or computer.

TanDEM-X: A New High Resolution Interferometric SAR Mission. TanDEM-X and TerraSAR-X in formation flight.

A Roundabout System:

Satellite systems are designed to overcome the primary limit of a land based broadcasting system; the planet’s horizon, which will eventually block out the signal from even a very tall tower. Combined with interference from buildings, trees, hills, etc., the range of a standard land based transmission is very limited. A signal from a one hundred foot tall tower would begin to be cut off after only 20 kilometers.

Consider a satellite, orbiting at nearly 43,000 Kilometers above the equator as the tallest possible tower available. Nothing should get in the way of that. But first, you need to get the programming up there.

Satellite programming providers assemble the shows and feeds they want here on Earth, and beam them up to the Astra group using massive, focused transmitters. These signals are captured, stored, and streamed back down to Earth at the appropriate times. The delay can be several seconds for live feed to several minutes for pre-recorded programming.

Meanwhile, back on Earth, Satellite TV subscribers are waiting with their dish shaped antennae to receive these signals from space. While there are some unusual designs available, the majority of the satellite dishes use the decades old parabolic dish technology which has served us well since the early Radar installations of World War II.

Basically, the dish part, usually between .5 meters and 1 meter across in urban areas, consists of a curved surface specially designed to reflect the signals from its entire surface to a small receiving antenna suspended above it.

The size of the dish depends on many factors, but the most common are local regulations and available funds. Urban and suburban installations are regulated by local laws as to what size dish can be deployed, while out in the country, larger dishes may be allowed.

Naturally, the larger the dish, the better it works, but also the more it costs, which is another limiting factor.



While the old TV antennas were designed to filter out frequencies from a flood of signals from various towers, the dish needs to focus its attention on the satellite itself. So not only must it be outside the house with no buildings, trees or poles in the way, it must be aimed as closely as possible towards the satellite’s position.

Installation is not beyond the reach of the basic do it yourselfer, but it is an involved process. The basic steps include:

  • Assembling the Satellite Dish: This is much easier with modern modular designs that it was back in the early days.
  • Mounting the Dish: Thiscan be done on a dedicated pole or attached to some part of your structure. Check the basic direction that the dish will point to make sure that no trees, towers, poles or smoke stacks interfere with the beam. (Your instructions will have charts to help with this step.)
  • Initial aiming: You will have directions to:
  • Set the Polarization: The angle that the receiver is away from the line of the horizon
  • Elevation: The angle that the dish pints up or down from true level.,
  • Azimuth: The direction the dish is pointing according to compass readings.
  • Final Aiming: Your installation kit should include a test device, usually audio, that will help you to fine tune you’re aiming to get the strongest signal.

Connect the Cables: This will involve stringing cables and applying connectors to the one or both ends.



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