parajumper männer Satellite Terminology
from the satellite for a ground based receiving antenna). The beamwidth is measured in a plane containing the direction of maximum signal strength. It is usually expressed as the angular separation between the two directions in which the signal strength is reduced to one half of the maximum value (the 3 db half power points).
(XPI). The ratio of the signal power received (or transmitted) by an earth station on one polarisation (the desired signal) to the signal power received (transmitted) on the same polarisation but originating from a cross polar signal. This ratio is usually expressed in decibels. It is a measure of interference from cross polar signals into the desired signal, which occurs in all practical systems that exploit both orthogonal polarisation. Strictly speaking, the terms „cross polar isolation“ and „cross polar discrimination“ have different meanings but are often used interchangeably.
Digital Video Broadcasting. A coherent set of European standards for transmission and reception of digital television signals via satellite, cable or terrestrial means, developed under the auspices of the Digital Video Broadcasting project and formalised by the European Telecommunication Standards Institute (ETSI). Although European, the standards have been adopted in many countries worldwide. There are many standards within the DVB family, including specifications for satellite (DVB S), cable (DVB C) and terrestrial (DVB T) transmission and reception.
A technique for utilising a specified range of frequencies more than once within the same satellite system so that the total capacity of the system is increased without increasing its allocated bandwidth. Frequency reuse schemes require sufficient isolation between the signals that use the same frequencies so that mutual interference between them is controlled to an acceptable level. Frequency reuse is achieved by using orthogonal polarisation states (horizontal/vertical for linear, or LHC/RHC for circular) for transmission and/or by using satellite antenna (spot) beams that serve separate, non overlapping geographic regions.
An orbit that approximates the geostationary orbit but whose plane is tilted slightly with respect to the Equatorial plane, with the consequence that the satellite appears to move about its nominal position in a daily „figure of eight“ motion when viewed from the ground. Satellites are often allowed to drift into an inclined orbit near the end of their nominal lifetime in order to conserve fuel on board the satellite,
which would otherwise be used to correct this natural drift caused by the gravitational pull of the Sun and the Moon.
Multiple Channel Per Carrier. Refers to the multiplexing of a number of digital channels (video programmes, audio programmes and data services) into a common digital bit stream, which is then used to modulate a single carrier that conveys all of the services to the end user. The single carrier supports multiple communication channels, hence the phase „multiple channel per carrier“. The term MCPC is frequency used in the context of DVB systems, where the composite digital signal is referred to as a Transport Stream.
The phenomenon in which radio waves are restricted to certain directions of electrical and magnetic field variations, where these directions are perpendicular to the direction of wave travel. By convention, the polarisation of a radio wave is defined by the direction of the electric field vector. Four senses of polarisation are used in satellite transmissions: horizontal (X) linear polarisation, vertical (Y) linear polarisation, right hand circular polarisation and left hand circular polarisation.
Satellite Master Antenna TV. Collective television reception and distribution system serving a local population of users collocated in a block of flats, a hotel or other group housing complex. SMATV systems use one or more high quality, centrally located antenna to receive the satellite signals, plus UHF and/or VHF antennas to receive local terrestrial broadcast services. The satellite and terrestrial signals are distributed to the end users via a dedicated cable distribution network. Several different cable distribution architectures are possible.