Biswajit.HD
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Television satellite signals originate from a single 'uplink' facility and are transmitted to a communications satellite orbiting 22,300 miles above the earth's equator. These type orbiting communications satellites are considered to be 'parked' in orbit; though in reality they travel from west to east but appear stationary to an observer on Earth because their speed is the exact speed of the Earth's rotation thus they are termed geostationary satellites. The overwhelmingly common receive frequency of satellite transmissions, for video purposes, are either in the C-band (frequency range from 3.7 to 4.2 gigahertz) or in the Ku-band (10.7 to 11.7 Ghz and 11.7 to 12.75 Ghz). New generation satellites are being built with Ka-band capability (22Ghz) and a very few, older specialty satellites are in the lower frequency S-band. After receiving the signals from earth, the satellite amplifies the signals then rebroadcasts them, or 'downlinks', back to earth in a predetermined beam pattern commonly called a 'footprint'. The calibration of the footprint is in EIRP (effective irradiated power) and its units are in dBw (decibel watts).
The downlinked signal from the satellites, upon reaching the earth, is very weak not only because of the great distance the signal has traveled but also because of the 'spreading' effect of the signal from a point source at the satellite to a regional image at its footprint. To begin the process to receive this signal, in effect, a satellite dish is a passive amplifier in that it 'collects' the weak signals from space, thus the bigger the dish the greater the signal amplication which is why a larger dish is required to receive satellite signals that are weak into your receiving location. A satellite dish collects these weak signals and focuses (reflects) the energy to a central spot known as the focal point or focus. All satellite dishes are designed according to a family of mathematical formulae known as parabolas (dish design formula). All incoming signals to a parabolic reflector are 'bounced' to the same point - this point is known as the focus (or focal) point of the dish. Ideally, all incoming signals from the orbiting satellite are reflected to the focal point. If the dish is properly installed and has no major surface irregularities, the reflected incoming energy will be tightly concentrated at the focus, therefore maximizing dish gain. Note that an offset dish is simply a section of the total parabola.
The downlinked signal from the satellites, upon reaching the earth, is very weak not only because of the great distance the signal has traveled but also because of the 'spreading' effect of the signal from a point source at the satellite to a regional image at its footprint. To begin the process to receive this signal, in effect, a satellite dish is a passive amplifier in that it 'collects' the weak signals from space, thus the bigger the dish the greater the signal amplication which is why a larger dish is required to receive satellite signals that are weak into your receiving location. A satellite dish collects these weak signals and focuses (reflects) the energy to a central spot known as the focal point or focus. All satellite dishes are designed according to a family of mathematical formulae known as parabolas (dish design formula). All incoming signals to a parabolic reflector are 'bounced' to the same point - this point is known as the focus (or focal) point of the dish. Ideally, all incoming signals from the orbiting satellite are reflected to the focal point. If the dish is properly installed and has no major surface irregularities, the reflected incoming energy will be tightly concentrated at the focus, therefore maximizing dish gain. Note that an offset dish is simply a section of the total parabola.
