Very Small Aperture Terminal

A Very Small Aperture Terminal (VSAT ) is a satellite receiver and transmitter with antenna ( aperture ) for satellite communications. Unlike the stationary Small Aperture Terminal satellite ground stations can VSAT systems are also mobile mounted on trucks or containers.

Standards and Technology

The diameter of a VSAT satellite dish is the 50 - to 100 - times the wavelength. Compared with optical systems they are small. Because there is the ratio of diameter and wavelength greater than 1000.

VSAT antennas are less than 2 m for the Ka-band, 4 m for the Ku-band and 8 m for the C-band. They lie between the high-gain antennas, in ESTRACK network as they are used, for example, and the so-called ultra- small aperture terminals for the private satellite channels. Often referred to all mobile antennas as VSAT.

The market offers different systems for data transmission. The most widely used systems currently found by Hughes, iDirect or Viasat. Viasat based on the DVB- RCS standard and sends a DVB/MPEG2-Signal. The system components are not compatible with the exception of receivers and transmitters at the satellite antenna in the rule or be excluded for reasons of competition for use with other providers. Nevertheless, the construction of a VSAT usually looks very similar.

Components

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

• Satellite Modem: A depending on the provider default differently blank modem to connect from the network and transmit / receive unit. The prices typically move between 300 and 1500 euros. The modems are usually " commissioned " sold, ie they only work with the original seller and can be used only by an activation with other providers.
• Block Up Converter ( BUC): transmitter to the satellite antenna. Are normally used Ku-band or C- band transmitter. The transmitting power between 1 and 4 watts, larger capacities are available, but are not available for VSAT for security available. Ku-band systems are due to the cheaper hardware on the rise, but disadvantage is the bandwidth sharing with other participants (called " contention ratio" ), which subjects payloading and thus bandwidth of its own system strong fluctuations. The providers offer but also as "full dedicated" designated at full bandwidth. A distinction is inverting and non-inverting BUC: Starting from the base band in which the information is according to the systems theory, both in the positive and in the mirror, negative frequencies can now both frequency bands ( the positive or negative ) to the desired location in the RF area shifted ( mixed) are. If this happens with the positive frequencies in the baseband, one speaks of the non-inverting operation. If the negative frequencies are mixed to the desired position, it is the inverting operation because the amplitude response of the inverted signal is exactly the opposite.
• Low Noise Converter: receiver (receiver) of the terminal. The technique is very similar to the modules used in television satellites. In general, the LNC is the lowest component of the system.
• Antenna: In Europe and North America usually ranging from parabolic mirrors with diameters from 0.9 to 1.2 meters for a good quality signal in the Ku- band. The upper limit of the antennas used in VSAT is about 4 m. Prices range between 200 and 2000 euros depending on size and quality. Many providers require certified mirror, but often also works another antenna.
• Transceiver: BUC and LNB can also be accommodated in one unit. This saves the complicated separation of the signaling pathways that can be built much more easily and is less susceptible to interference. Because of the different polarization of the signals from different satellites but can not be inserted at each satellite, each transceiver.

Available satellite

A selection of currently popular provider

• Eutelsat: Euro Bird series, AB series, Seasat 2, W - series. Area Covered: Europe, North Africa and Sub -Saharan Africa, Middle East, South America, Southeast Asia.
• PanAmSat PAS series. Area Covered: North and South Africa, Europe
• More suppliers: News gravel, Hellasat
• ND SatCom
• Intelsat

Applications of VSAT

• Internet access
• Voice and fax transmission
• Connections between Local Area Networks
• Internet telephony or VoIP
• Data transmission
• Video conferencing