How is Two way VSAT satellite internet technology possible ?
Satellite broadcasting is made possible by the fact that communications satellites are fixed in geosynchronous orbit 22,300 miles above the equator, staying in the same position above the ground at all times. This allows two way satellite antenna’s that transmit and receive signals to be aimed at an orbiting satellite and left in a fixed position. Satellite programmers broadcast, or uplink, signals to a satellite which they either own or lease channel space from. The signals are often scrambled, or encrypted, to prevent unauthorized reception before they are retransmitted to a home satellite antenna. The uplinked signals are received by a transponder located on the satellite, a device that receives the signals and transmits them back to the earth after converting them to a frequency that can be received by a ground-based satellite antenna. Typically there are 24 to 32 transponders on each satellite. In order to minimize interference between the satellite transponders, the signals are transmitted with alternately polarized antennas. Each satellite occupies a particular location in orbit, and operates at a particular frequency assigned by the FCC.
Satellite signals and technology
The signals received at the satellite from a ground-based antenna are extremely weak in amplitude – much less than one watt. As a result, they must employ amplifiers that boost the signals to a level that can successfully be processed and retransmitted to the earth. After traveling 22,000 miles to a ground-based antenna, the signals are again very weak and must be amplified. Therefore, satellite “dishes” focus the signals onto the actual antenna. The signals from the antenna are then fed to a “low-noise block,” or LNB, amplifier which amplifies signal and converts them to a lower frequency. The lower the power of the satellite, the larger the antenna required to focus the signals. A C-Band satellite, with power ranging between 10 and 17 watts per transponder, typically has an antenna between 5 and 10 feet in diameter; whereas a high-powered Ku-Band satellite, with a range of 100 to 200 watts per transponder, only requires an antenna 18 inches in diameter. The signals from the antenna are fed to an integrated receiver/decoder (IRD), which converts them to a form that can be tuned by a TV set. Every IRD contains a unique address number, which is activated by a satellite programmer to allow it to receive subscription services. In addition, the IRDs modem port is connected to a telephone line, in order to access pay-per-view ordering services and transmit other data. A single IRD can supply one channel choice to one or more TV sets. In order to view two different programs at the same time on two different TV sets, two IRDs are required—one for each TV, and the antenna must be a dual-LNB type.
What is a VSAT?
A VSAT is a small-sized telecommunications earth station that transmits and receives via satellite. The terminal size is 1.2 to 2.4 meters in diameter. VSAT stands for Very Small Aperture Terminal – its a catchy acronym and as such its been adopted by all and sundry for every type of satellite product from small components of a system to complete systems. Because the term really hinges around the small size of the antenna it has been used to describe both one-way and interactive systems. Specifically, we in the industry, isolate television broadcast receivers because counting these as well would simply distort the numbers in the marketplace, but data, audio and, to some extent, voice systems are included. Generally, these systems operate in the Ku-band and C-band frequencies. As a rule of thumb C-band (which suffers less from rain attenuation, but requires larger antennas) is used in Asia, Africa and Latin America whilst Ku-band (which can use smaller antennas, but suffers from rain fade in a monsoon-like downpour) is used in Europe and North America. Typically, interactive Ku-band antenna sizes range from 75 centimetres to 1.8 metres and C-band from 1.8 metres to 2.4 metres. One way systems can use antennas as small as 45 centimetres.
