Very Small Aperture Terminal

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VSAT C-band antenna

A Very Small Aperture Terminal ( VSAT ) is a satellite receiver and transmitter with antennas ( aperture ) for satellite-based communication. In contrast to the fixed small aperture terminals of the satellite ground stations, VSAT systems can also be mounted on trucks, containers or ships.

Standards and technology

The diameter of a VSAT parabolic antenna is 50 to 100 times the wavelength. They are small compared to optical systems. Because there the ratio of diameter and wavelength is greater than 1000.

VSAT antennas are smaller than 2 m for the Ka band , 4 m for the Ku band or 8 m for the C band . They are between the high gain antennas, as they are, for. B. be used in the ESTRACK network, and the so-called ultra small aperture terminals for private satellite reception. All mobile antennas are often referred to as VSAT.

The market offers different systems for data transmission. Systems from Hughes , iDirect or Viasat are currently most popular . Viasat is based on the DVB-RCS standard and sends a DVB / MPEG2 signal. With the exception of receivers and transmitters on the satellite antenna, the system components are generally not compatible or, for reasons of competition, cannot be used with other providers. Nevertheless, the structure of a VSAT usually looks very similar.

Components

A VSAT for connecting a computer or network usually consists of the following components

  • Satellite modem : Depending on the provider standard, a modem designed differently to connect the network and the transmitter / receiver unit. The prices move i. d. Usually between 300 and 1500 euros. The modems are mostly sold “commissioned”, ie they only work with the original provider and can only be used if they are activated with other providers.
  • Block Up Converter (BUC): Transmitter unit on the satellite antenna. Usually Ku-band or C-band transmitters are used. The transmission powers are between 1 and 4 watts, higher powers are available, but are not available for VSAT for security reasons. Ku-band systems are on the advance because of the cheaper hardware, but the disadvantage is the bandwidth sharing with other participants (so-called "contention ratio"), which subjects the capacity and thus the bandwidth of your own system to strong fluctuations. However, the providers also offer full bandwidths called “full dedicated”. A distinction is made between inverting and non-inverting BUC: Starting from the baseband, in which the information is located in both the positive and the mirrored, negative frequencies according to system theory , both frequency bands (the positive or the negative) can now be placed in the desired position in the HF Area can be moved (mixed). If this happens with the positive frequencies in the baseband, one speaks of non-inverting operation. If the negative frequencies are mixed at the desired point, then it is the inverting mode, because the amplitude response of the inverted signal is exactly the opposite.
  • Low Noise Converter (LNC): Receiver of the terminal. The technology is very similar to the modules used in television satellites. Usually the LNC is the cheapest component of the system.
  • Antenna : In Europe and North America, parabolic mirrors with a diameter between 0.9 and 1.2 meters are usually sufficient for good signal quality in the Ku band. The upper limit of the antennas used at VSAT is around 4 m. The prices are between 200 and 2000 euros depending on the size and quality. Many providers require certified mirrors, but another antenna often works as well.
  • Transceiver : BUC and LNC can also be accommodated in one unit. This saves the complicated separation of the signal paths, is much easier to set up and is less prone to interference. Due to the different polarization of the signals from different satellites, not every transceiver can be used on every satellite.

Available satellites

A selection of currently popular providers

  • Eutelsat : Eurobird series, AB series, Seasat 2 , W series. Area coverage: Europe, North Africa and Sub-Sahara, Near and Middle East, South America, Southeast Asia.
  • PanAmSat : PAS series. Area coverage: North and South Africa, Europe
  • Other providers: NewSkies , Hellasat
  • ND SatCom
  • Intelsat

Applications of VSAT

Web links