ABC-ului receptiei prin satelit!

[gessle]

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In curand ,voi incepe acest topic!

[gessle]

Pt un inceput:lexicon


A/B Switch:
A switch that selects one of two inputs (A or B) for routing to a common output while providing adequate isolating between the two signals.

Access Control System - ACS:
Access Control System/s, comprising all conditional access components such as S/1, IDAC, ISAC, minicons, etc...

ACS number:
This is the version number of the cards software.
There are several different software versions: 1.2, 1.4, 1.6 en 3.82, 3.83.
Versions 1.4 and 1.6 are almost identical.

Adaptation Header:
A block of data that forms an extension to a transport packet header. It may be of fixed format and/or of general data

Adjacent Channel:
An adjacent channel is immediately next to another channel in frequency. For example, PAL channels 5 and 6 as well as 8 and 9 are adjacent.

Alignment:
The process of fine tuning a dish or an electronic circuit to maximize its sensitivity and signal receiving capability.

Alphacrypt:
The Irdeto successor, decodes both Irdeto and Betacrypt.

AM:
An abbreviation for amplitude modulation.

Analog:
A system in which signals vary continuously in contrast to a digital system in which signals vary in discrete steps.

Analogue-to-Digital Converter:
A circuit that converts analogue signals to an equivalent digital form. The varying analogue signal is sampled at a series of points in time. The voltage at each of these points is then represented by a series of numbers, the digital value of the sample. The higher this sampling frequency, the finer are the gradations and the more accurately is the signal represented

Antenna:
A device that collects and focuses electromagnetic energy, i.e., contributes an energy gain. Satellite dishes, broadband antenna and cut-to-channel antennas are some types of antennas encountered. In the case of satellite dishes, gain is proportional to the surface area of the microwave reflector.

Antenna Efficiency:
The percentage of incoming satellite signal actually captured by an antenna system.

Aperture:
The collection area of a parabolic dish.

Aperture Blocking:
An obstruction such as the feed assembly which causes a blocking of the incoming signal.

Asciiserial:
The number that identifies the card. It is also printed on the card in bar-code.
Although it is accessible by software, to my knowledge it is never really used.
It only serves identification purposes.

Aspect Ratio:
The ratio of television screen width to height. The standard aspect ratio is 4 to 3.

Aston Seca:
Although the real name for the coding system is Mediaguard, it is often referred to as Seca or Aston Seca. Mediaguard is developed by Seca, so the also used name Seca Mediaguard is more suitable. Aston is a company that builds the CAM's (among others) that are used to decode the Mediaguard system.
The Seca Mediaguard coding is used by the Canal + organization which is no wonder. Canal + is shareholder in the Seca organization and it also takes part in the development of the Mediaguard coding system. Because of the influence of Canal +, the Seca Mediaguard system is very popular in France.

Attenuation:
The decrease in signal power that occurs in a device or when a signal travels to reach a destination point (path loss).

Attenuator:
A passive device which reduces the power of a signal. Attenuators are rated according to the amount of signal attenuation.

ATR:
Answer To Reset, or ATR for short, is the string a smart card sends to the receiver upon every reset. The ATR of each smart card conforms to the ISO7816-3 specifications. The ATR contains information about the card, for instance information on how the receiver should communicate with the card: Voltage, Amp, Baudrate, Synchronous or Asynchronous communication etc.

Audio Subcarrier:
The carrier wave that transmits audio information within a video broadcast signal. Satellite transmissions can relay more than a single audio subcarrier in the frequency range between 5 and 8.5 MHz.

Auto Update:
The auto update (AU) technique makes sure the card is kept up to date in order to provide the correct keys to the CAM when requested. Providers will regularly change their operational keys and unless you have a valid set of management keys, you will soon be left with a black screen. For different coding systems, the actual keys that are used for decoding, have different names. For instance, in Irdeto they are called Plainkeys and for Seca they are called Operational Keys.

Automatic Brightness Control:
A television circuit used to automatically adjust picture tube brightness in response to changes in background or ambient light.

Automatic Fine Tuning:
A circuit that automatically maintains the correct tuner oscillator frequency and compensates for drift and for moderate amounts of inaccurate tuning. Similar to AFC.

Automatic Frequency Control - AFC:
A circuit that locks an electronic component to a chosen frequency, so that the the tuning will not drift from that chosen frequency.

Automatic Gain Control - AGC:
A circuit that uses feedback to maintain the output of an electronic component at a constant level. This is achieved by locking the gain onto a fixed value and thus compensating for varying input signal levels keeping the output constant.

Azimuth-Elevation (Az-El) Mount:
A dish mount that tracks satellites by moving in two directions: the azimuth in the horizontal plane and elevation up from the horizon.

Azimuth:
A compass bearing expressed in degrees of rotation clockwise from true north. It is one of the two coordinates, azimuth and elevation, used to align a satellite dish.

Band:
A range of frequencies.

Band Separator:
A device that splits a group of specified frequencies into two or more bands. Common types include UHF/VHF, Hi/Lo-band and FM separators. This device is essentially a set of filters.

Bandpass Filter:
A circuit or device that allows only a specified range of frequencies to pass from input to output.

Bandwidth:
The frequency range allocated to any communication circuit.

Baseband:
The raw audio and video signals prior to modulation and broadcasting. Most satellite headend equipment utilizes baseband inputs. More exactly, the composite unclamped, non-de-emphasized and unfiltered receiver output. This signal contains the complete set of FM modulated audio and data subcarriers

Beamwidth:
A measure used to describe the width of vision of a dish. Beamwidth is measured as degrees between the 3 dB half power points

Betacrypt:
A coding system very similar to Irdeto and used by the German provider Premiere World.

Bit Error Rate - BER:
The number of errors in a data stream usually expressed a ratio to the total number of bits in which an error occurs. For example, 1 in 10 7 or 10 -7

Bits per Second - BPS:
The number of bits transmitted each second

Blanking Pulse Level:
The reference level for video signals. The blanking pulses must be aligned at the input to the picture tube.

Blanking Signal:
Pulses used to extinguish the scan illumination during horizontal and vertical retrace periods.

Block Downconversion:
The process of lowering the entire band of frequencies in one step to some intermediate range to be processed inside a satellite receiver. Multiple block downconversion receivers are capable of independently selecting channels because each can process the entire block of signals.

Blocker:
Every now and then, some providers will send signals that will effect pirate cards only. The intention of these signals is to disable pirate cards. In order to make sure these unwanted signals don't reach and disable your original card, you can use a blocker. There are 2 ways to block signals: software- and hardware blockers.

Bootloader:
A bootloader is the first program, executed whenever you turn your receiver on. The bootloader will ensure that the receivers operating system is started. The operating system of a satellite receiver is usually called the firmware.

Bouquet:
A group of services offered. The operator may also market a bouquet as a product such as `The Basic Bouquet.'

Broadband:
A device that processes a signal(s) spanning a relatively broad range of input frequencies

C-Band:
The 3.625 to 4.2 GHz band of frequencies at which some broadcast satellites operate.

Card doubler:
A device that enables you to use 2 cards in 1 CAM simultaneously.

Card group:
A card group is just another name for provider group.

Carrier:
A pure-frequency signal that is modulated to carry information. In the process of modulation it is spread out over a wider band. The carrier frequency is the center frequency on any television channel.

Carrier-to-Noise Ratio - C/N:
The ratio of the received carrier power to the noise power in a given bandwidth, expressed in decibels. The C/N is an indicator of how well an receive system will perform in a particular location, and is calculated from satellite power levels, dish gain and the system noise temperature.

Cassegrain Feed System:
A dish feed design that includes a primary reflector, the dish, and a secondary reflector which redirects microwaves via a waveguide to a low noise amplifier.

CB20 selection:
A smart card can be addressed and modified in 3 ways:
1. By using the hex serial, individual cards can be addressed
2. Through the card group number, all 256 cards in that group can be addressed simultaneously
3. Within a card group a selection of individual cards can be addressed by means of a CB20 selection (max. 256 cards)

CCD:
Charge coupled device. In this device charge is stored on a capacitor which are etched onto a chip. A number of samples can be simultaneously stored. Used in MAC transmissions for temporarily storing video signals.

Channel:
A segment of bandwidth used for one complete communication link.

Channel ID:
Is used to select a channel.
The correct combination of key and channel ID will activate the key.

Characteristic Impedance:
The impedance in ohms of a device in the path of a communication signal such as a cable, a connector or the input of an amplifier.

Chrominance:
The hue and saturation of a color. The chrominance signal is modulated onto a 4.43 MHz carrier in the PAL television system and a 3.58 MHz carrier in the NTSC television system.

Chrominance Signal:
The color component of the composite baseband video signal assembled from the I and Q portions. Phase angle of the signal represents hue and amplitude represents color saturation.

Circular Polarity:
Electromagnetic waves whose electric field uniformly rotates along the signal path. Broadcasts used by Intelsat and other international satellites use circular, not horizontally or vertically polarized waves as are common in North American and European transmissions

Clamp Circuit:
A circuit that removes the dispersion waveform from the downlink signal.

Clamped Outputs:
Satellite receiver outputs that have the energy dispersal waveform removed. Unclamped outputs are often required as input to a decoder.

Clarke Belt:
The circular orbital belt at 35 786 kilometers above the equator, named after the writer Arthur C. Clarke, in which satellites travel at the same speed as the earth's rotation. Also called the geostationary orbit.

Coaxial Cable:
A cable for transmitting high frequency electrical signals with low loss. It is composed of an internal conducting wire surrounded by an insulating dielectric which is further protected by a metal shield. The impedance of coax is a product of the radius of the central conductor, the radius of the shield and the dielectric constant of the insulation. In most satellite and SMATV systems, coax impedance is 75 ohms.

Color Sync Burst:
A burst of 8 to 11 cycles in the 4.43361875 MHz (PAL) or 3.579545 MHz ( NTSC) color subcarrier frequency. This waveform is located on the back porch of each horizontal blanking pulse during color transmissions. It serves to synchronize the color subcarrier's oscillator with that of the transmitter in order to recreate the raw color signals.

Common Interface:
Common Interface (CI) is a PCMCIA slot in the satellite receiver in which CAM'scan be put. All multicryptreceivers use Common Interfaces.

Common Scrambling Algorithm :
This is the coding algorithm as specified by DVB. The CSA was designed to make transmitted signals safe from hackers. For the provider the real advantage is that CSA is universal to several types of CAM's. This means that a provider who for instance broadcasts in both Seca and Viaccess, can send EMM'sand ECM's with the transmission, but each CAM will only react to the commands which are meant for that CAM. All other commands are ignored.

Composite Baseband Signal:
The complete audio and video signal without a carrier wave. Satellite signals have audio baseband information ranging in frequency from zero to 3400 Hertz. NTSC video baseband is from zero to 4.2 MHz.
PALvideo basebandranges from 0 to 5.5 MHz.

Composite Video Signal:
The complete video signal consisting of the chrominance and luminance information as well as all sync and blanking pulses.

Companding:
A form of noise reduction using compression at the transmitting end and expansion at the receiver. A compressor is an amplifier that increases its gain for lower power signals. The effect is to boost these components into a form having a smaller dynamic range. A compressed signal has a higher average level, and therefore, less apparent loudness than an uncompressed signal, even though the peaks are no higher in level. An expander reverses the effect of the compressor to restore the original signal.

Compressor:
A unit that accepts uncompressed video, audio and data and then digitizes and compresses these signals

Compression System:
A collection of compressors, multiplexers and modulators that generate one multiplex signal

Conax:
A coding system which is used a lot in the Scandinavian countries.

Conditional Access:
Conditional Access (CA) is a technology, used for coding and authorizing in DVBsystems. The control mechanism is used to limit access by decoders to only the subscribed or free services on a multiplex.
A Conditional Access System (CAS) contains a few basic elements: SMSand SAS.

Conditional Access Module (CAM):
A Conditional Access Module (CAM) is the module into which the CA system is built in. CAM's can be found as separatemodules to put into the CIof your receiver, but they are also sometimes built fix into the receiver. In that case they are called embedded CAM.
The CAM contains all software, needed to decode a certain scrambling system and also the necessary software to enable it to communicate with your smart card.

Conditional Access Table (CAT):
Conditional Access Table. A table that relates entitlement management message ( EMM) data streams to the conditional access ( CA) vendor(s) managing the decoder base.

Control Word:
A Control Word (CW) is a data package containing the coded key for the coding algorithm of your smart card.

Countrycode (COCO):
A 3 digit code, used to inform the CAM/receiver which group of channels should be validated.

Crd's:
You can regard Crd files as a kind of macro files. They contain command strings, used to update your smart card.

Cross Modulation:
A form of interference caused by the modulation of one carrier affecting that of another signal. It can be caused by overloading an amplifier as well as by signal imbalances at the headend.

Cross Polarization:
Term to describe signals of the opposite polarity to another being transmitted and received. Cross-polarization discrimination refers to the ability of a feed to detect one polarity and reject the signals having the opposite sense of polarity

Crosstalk:
Interference between adjacent channels often caused by cross modulation. Leakage can occur between two wires, PCB tracks or parallel cables.

Cryptedkey (Key) & Plainkey:
These are respectively a coded and a uncoded form of the same key.
To make things even more complicated than they already are, the cryptedkey is often simply referred to as key.
The cryptedkey contains a combination of the date, that key was sent, the plainkey and the Plainmasterkey, all coded into 1 key. The cryptedkey is sent to the card on a regular basis. It validates the subscription of the user, therewith enabling the user to view certain channels. The cryptedkey ensures correct decoding of a validated channel. The plainkey is the uncoded version of the cryptedkey.

Crypto Works:
A relative newcomer among the coding systems is Crypto Works. This system is developed by the Dutch based Philips.

Customer Word Pointer:
The 4th byte in the PPUAstring is called the CWP (or Customer Word Pointer). It is used to address individual cards. The CWP is used only in MOSC cards.

Date:
The date on a card is used by the provider to activate or deactivate channels.

De-emphasis:
A reduction of the higher frequency portions of an FM signal used to neutralize the effects of pre-emphasis. When combined with the correct level of pre-emphasis, it reduces overall noise levels and therefore increases the output S/N ratio

Declination Offset Angle:
The adjustment angle of a polar mount between the polar axis and the plane of a satellite antenna used to aim at the geosynchronous arc. Declination increases from zero with latitude away from the equator.

Decoder:
A circuit that restores a signal to its original form after it has been scrambled.

Decoder Management:
A sub-system on the BS, managing all decoder/smartcard related information such as function testing, keysafing information, etc...

Decoding Time Stamp - TS:
A 90 kHz referenced time stamp indicating when the contents of a packetized elementary stream (PES) packet should be decoded

Demodulator:
A device which extracts the baseband signal from the transmitted carrier wave.

Digital:
Describes a system or device in which information is transferred by electrical [on-off], [high-low], or [1/0] pulses instead of continuously varying signals or states as in an analog message.

Direct Broadcast Satellite (DBS):
A term commonly used to describe Ku-band broadcasts via satellite directly to individual end-users. The DBS band ranges from 11.7 to 12.75 GHz.

Direct programming lines:
If the eeprom on a card is directly connected to the cards contacts, then the eeprom can be programmed independently from the processor. When this is the case, those direct connections are called the direct programming lines. You will find DPL on SMD or HMD cards only. Goldwafers don't utilize DPL and will therefor always need a loader file in the processor chip in order to program the eeprom on the card.

Downconverter:
A circuit that lowers the high frequency signal to a lower, intermediate range. There are three distinct types of downconversion used in satellite receivers: single downconversion; dual downconversion; and block downconversion.

Downlink Antenna:
The antenna on-board a satellite which relays signals back to earth.

DPSC:
DPSC is short for Digital Pirate SatelliteCard. These cards are sold with working keys. Prices can be up to several hundreds of Euros for multi provider cards. Usually these cards contain a sort of timing routine which ensures that the cards are disabled after a certain period of use. But these cards will also be closed by provider attacks through the use of ECM's.

Drifting:
An instability in a preset voltage, frequency or other electronic circuit parameter.

DTH:
Direct-To-Home satellite broadcasts.

Dual-Band Feed:
A feed which can simultaneously receive two different bands, typically the C and Ku-bands.

DVB:
DVB is short for Digital Video Broadcasting, or digital satellite TV.

DVB Bouquet:
The DVB SI tables includes a Bouquet Association Table (the BAT). The DVB definition for a "bouquet" is "a group of services logically grouped together". The intention of the DVB Bouquet is usually to group services that are managed by one entity together. "DVB" is added before the name to distinguish it from the "SMS" bouquet.

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Earth Station:
A complete satellite receiving or transmitting station including the dish, electronics and all associated equipment necessary to receive or transmit satellite signals. Also known as a ground station.

ECM:
ECM is short for Entitlement Control Message. These are commands which are used to control the working of your card. ECM's are always sent as packets. Such a packet is called a Control Word(CW) and it contains coded keys, ID's etc. needed to decode the signal. In other words, the ECM identifies the service and the conditions that have to be met in order to use that service. Providers will also use fake ECM's to disable pirate cards. That is why a lot of people translate ECM as Electronic Counter Measure.

Effective Isotropic Radiated Power (EIRP):
A measure of the signal strength that a satellite transmits towards the earth below. The EIRP is highest at the center of the beam and decreases at angles away from the boresight.

Electronic Program Guide (EPG):
The Electronic Program Guide is broadcasted along with all other data.

Elementary Stream (ES):
A stream carrying a single stream of, typically of presentation data, such as a single audio or video data stream

Elementary Stream Clock Reference (ESCR):
Elementary Stream Clock ReferenceA 42-bit counter clocked at 27 MHz which is used for synchronizing data

Elevation Angle:
The vertical angle measured from the horizon up to a target satellite.

EMM:
EMM is short for Entitlement Management Messages. EMM's are composed of the information, contained in the SASand will always be sent together with the ECM. EMM's contain information about the subscriber and the status of the subscription. They are used to transfer information about authorization, but they will also carry new keys, or modify or delete existing keys.

Encoder:
An entity that compressed a single data stream

Energy Dispersal:
The modulation of an uplink carrier with a triangular waveform. This technique disperses the carrier energy over a wider bandwidth than otherwise would be the case in order to limit the maximum energy compared to that transmitted by an unclamped carrier. This triangular waveform is removed by a clamp circuit in a satellite receiver.

EPG:
EPG is short for Electronic Program Guide.

Equalizing Pulses:
A series of six pulses occurring before and after the serrated vertical sync pulse to ensure proper interlacing. The equalizing pulses are inserted at twice the horizontal scanning frequency.

Event:
An event is one particular transmission of a program. An event is known by its name, the service on which it is transmitted, the date and time of its broadcast and possibly additional information such as a part number. Events may be re-broadcast if the events are different

F-connector:
A standard RF connector used to link coax cables with electronic devices.

f/D Ratio:
The ratio of a dish's focal length to diameter. It describes dish depth.

Feed:
A device that collects microwave signals reflected from the surface of a dish. It is mounted at the focus of all prime focus parabolic dishes.

Field:
One half of a complete TV picture or frame, composed of 325 scanning lines. In the PAL broadcast system there are 50 fields per second.

File set:
A file set is a complete package of software and keys, needed to program a smart card. How the file set is composed, is dependent on the type of card it is made for. For PIC cards, a file set contains 2 files (the PIC file and the eeprom file). For AVR type cards like the Fun- and Jupiter cards, the file set contains 2 or 3 files (a flash file for the processor, an external eeprom file and sometimes an internal eeprom file).

Filter:
A device used to reject all but a specified range of frequencies. A bandpass filter allows only those signals within a given band to be communicated. A rejection filter, the mirror image of a bandpass filter, eliminates those signals within a specified band but passes all other frequencies.

Firmware:
The firmware is the operating system software for the receiver

FM:
An abbreviation for frequency modulation Focal Length - The distance from the reflective surface of a parabola to the point at which incoming satellite signals are focused, the focal point. Footprint - The geographic area towards which a satellite downlink antenna directs its signal. The measure of strength of this footprint is the EIRP.

Forward Error Correction (FEC):
FEC is a technique for improving the accuracy of data transmission. Excess bits are included in the out-going data stream so that error correction algorithms can be applied upon reception. On satellite links this is in the form of Reed-Solomon and convoluted Viterbi coding implemented at modulator/demodulator level.

Frame:
One complete TV picture, composed of two fields and a total of 525 and 625 scanning lines in NTSCand PAL systems, respectively.

Frequency:
The number of vibrations per second of an electrical or electromagnetic signal expressed in cycles per second or Hertz. Front-end Processor - FEP

Gain:
The amount of amplification of input to output power often expressed as a multiplicative factor or in decibels.

Gain-to-Noise Temperature Ratio (G/T):
The figure of merit of a dish and LNA. The higher the G/T, the better the reception capabilities of an earth station.

Ghosting:
A term used to describe the appearance of multiple TV images that is usually caused by reception of a signal via two different paths.

GigaHertz (GHz):
1000 MHz or one billion cycles per second.

Global Beam:
A footprint pattern used by communication satellites targeting nearly 40% of the earth's surface below. Many Intelsat satellites use global beams.

Ground Noise:
Unwanted microwave signals generated from the warm ground and detected by a dish.

Hall Effect Sensor:
A semiconductor device in which an output voltage is generated in response to the intensity of a magnetic field applied to a wire. In an actuator, the varying magnetic field is produced by the rotation of a permanent magnet past a thin wire. The pulses generated serve to count the number of rotations of the motor

Hardline:
A low-loss coaxial cable that has a continuous hard metal shield instead of a conductive braid around the outer perimeter. This type of cable was used in the pioneer days of satellite television.

Headend:
The portion of an SMATVor MMDS system where all desired signals are received and processed for subsequent distribution.

Heliax:
A thick low-loss cable used at high frequencies; also known as hard-line.

Hertz:
An abbreviation for the frequency measurement of one cycle per second. Named after Heinrich Hertz, the German scientist who first described the properties of radio waves.

Hexserial:
A 3 byte hexadecimal number which is used by the provider to address the smart card.

Hexmasterkey:
A 10 byte long hexadecimal number which is coded with the hexserial. The hexmasterkey is just a code which is used by the smart card to calculate the plainmasterkeyfrom the masterkey. Without the hexmasterkey it is not possible to correctly update the plainmasterkey.

High Definition Television (HDTV):
An innovative television format having approximately twice the number of scan lines in order to improve picture resolution and viewing quality.

High Power Amplifier (HPA):
An amplifier used to amplify the uplink signal. Horizontal Blanking Pulse - The pulse that occurs between each horizontal scan line in an analogue television signal and extinguishes the beam illumination during the retrace period.

Horizontal Sync Pulse (HSP):
A 4.7 microsecond (in the PAL system) rectangular pulse riding on top of each horizontal blanking pulse. It synchronizes the horizontal scanning at the television set with that of the television camera.

HPA Room:
The space where radio frequency systems reside. These include modulators, group delay equalizers, upconverters, high power amplifiers and combiner systems

Hum Bars:
A form of interference seen as horizontal bars or black regions passing across the field of a television screen.

I Signal:
One of the two color video signals which modulate the color subcarrier. It represents those colors ranging from reddish orange to cyan.

Impedance:
The resistance to alternating current flow in an electrical circuit.

Impulse Pay Per View:
Impulse pay per view or interactive pay per view (ippv) is an extension of ordinary ppv. You no longer will be charged for a total event, but instead you are charged for the time you spent using the service.

Instructions:
Seca uses so called instruction bytes (INS) in order to communicate between CAMand smart card. These instructions are used for instance to request card- and provider data, authorization, ECM'sand EMM's etc.

Integrated Decoder Access Control:
IDAC Integrated Receiver Decoder - IRD - A satellite receiver and decoder contained in one case Interference - An undesired signal intercepted by a TVRO that causes video and/or audio distortion.

Integrated Receiver Decoder (IRD):
An integrated satellite receiver/decoder.

Insertion Loss:
The amount of signal energy lost when a device is inserted into a communication line. Also known as <169>feed through<170> loss.

Interlaced Scanning:
A scanning technique to minimize picture flicker while conserving channel bandwidth. Even and odd numbered lines are scanned in separate fields both of which when combined paint one frame or complete picture.

Intermediate Frequency (IF):
A middle range frequency generated after downconversion in any electronic circuitry including a satellite receiver. The majority of all signal amplification, processing and filtering in a receiver occur in the IF range.

Irdeto:
A organization, founded by Ir. den Toonder (hence the name). This organization develops systems for secure data distribution like ppv (pay per view) and ippv(impulse pay per view).
The most well known providers that use Irdeto for their transmissions, are Premiere World, Canal +, Stream and Nova.

Isolator:
A device that allows signals to pass unobstructed in one direction but which attenuates their strength in the reverse direction.

Isolation Loss:
The amount of signal energy lost between two ports of a device. An example is the loss between the feed through port and the tap/drop of a top-off device.

Key compatible card groups:
These are card groupsor provider groups, sharing the same keys.

Kilohertz (kHz):
One thousand cycles per second.

Ku-Band:
The microwave frequency band between approximately 11 and 13 GHz used in satellite broadcasting.

Line Amplifier:
An amplifier in a transmission line that boosts the strength of a signal.

Line Splitter:
An active or passive device that divides a signal into two or more signals containing all the original information. A passive splitter feeds an attenuated version of the input signal to the output ports. An active splitter amplifies the input signal to overcome the splitter loss.

Local Oscillator:
A device used to supply a stable single frequency to an upconverter or a downconverter. The local oscillator signal is mixed with the carrier wave to change its frequency.

Logging:
The process of recording the information contained in the data stream between CAMand smart card. The data stream contains, among others, the keys that are used by the provider to manipulate the card.

Low Noise Amplifier (LNA):
A device that receives and amplifies the weak satellite signal reflected by a dish via a feed. C-band LNAs typically have their noise characteristics quoted as noise temperatures rated in degrees Kelvin. Ku-band LNA noise characteristics are usually expressed as a noise figure in decibels.

Low Noise Block (LNB/LNBF):
LNB is short for L ow N oise B lock. Or to be even more accurate, Low Noise Block Downconverter. A LNB converts the frequency of the captured satellite signal to another frequency. A frequency that can be transported via Coax cable, to be precise. In home satellite systems, the Ku-band is converted to a much lower frequency. Indeed, through the use of a LNB.
LNBF is short for L ow N oise B lock F eedhorn. This is a LNB in which the feedhorn is already fully integrated. A feedhorn will bundle the energy, captured by your satellite dish. The bundled energy can then be processed by the LNB, much better.

Low Noise Converter (LNC):
An LNA and a conventional downconverter housed in one weatherproof box. This device converts one channel at a time. Channel selection is controlled by the satellite receiver. The typical IF for LNCs is 70 MHz.

Masterkey & Plainmasterkey:
The coded, respectively uncoded 8 byte key, used to trigger certain card functions like "opening" the card.
The Masterkey can be calculated from the sum of the hexserial and the provider group.
So the mathematical formula is simply: hexserial + provider group = masterkey.
The Masterkey is also sometimes referred to as Key00. Whenever the Masterkey is written to the card, that is done uncoded (the plainmasterkey). The plainmasterkey is necessary for further processing of the key- and channel information.

MegaHertz (MHz):
One millions cycles per second.

MMDS: Microwave Multipoint Distribution Services (see MUD)

Modulator:
A device that modulates a signal, for example an analog signal or an MPEG-2 transport stream onto a radio frequency carrier

Modulation:
A process in which a message is added or encoded onto a carrier wave. Among other methods, this can be accomplished by frequency or amplitude modulation, known as AM or FM, respectively.

MOSC:
Modified Original Smart Card. These are the original provider supplied smart cards.

MPEG:
MPEG is short for Moving Pictures Expert Group.
This is the organization that developed the MPEG standard.
MPEG comes in several versions:
- MPEG-1, mainly used for Video CD and MP3
- MPEG-2, the standard in digital TV, DVD and set top boxes
- MPEG-4, the multi media standard for the web

Multicrypt:
Multicrypt receivers are universal receivers that utilize common interfacesto serve as a carrier for separate CAM's. Multicrypt receivers have been developed under pressure of the market. Their flexibility lies in the possibility to host several CAM's, thus enabling them to accommodate multiple coding systems.

Multiple Analog Component (MAC) Transmissions:
A video/audio/data transmission method that separates the data, chrominance and luminance components and compresses them for sequential relay over one television scan line. There are a number of systems in use and under development including A-MAC, B- MAC, C-MAC, D-MAC, D2-MAC, E-MAC and F-MAC.

Multiple Unit Dwelling (MUD):
MUD Microwave Multipoint Distribution Services - MMDS - A system for distributing television programs via terrestrial microwaves to very small receive dishes

Multiplexing:
The simultaneous transmission of two or more signals over a single communication channel. The interleaving of the luminance and chrominance signals is one form of multiplexing, known as frequency multiplexing. MultiChoice transmissions use time division multiplexing (TDM) whereby data streams are divided in time into interspersed data packets.

Multiplexer:
MUX - A device that takes the outputs from a number of encoders and multiplexes them together to form one data stream

MUX Controller:
A computer that controls the functions of a specific multiplexer pair in a compression system

N-Connector:
A low-loss coaxial cable connector used at the elevated microwave frequencies.

NagraVision:
A coding system which is especially popular among Spanish and Turkish providers.

Nano Codes:
Nanos are commands, sent to the card in order to update the card.

NTSC:
The National Television Standards Committee which created the standard for North American TV broadcasts.

NTSC Color Bar Pattern:
The standard test pattern of six adjacent color bars including the three primary colors plus their three complementary shades.

Negative Picture Phase:
Positioning the composite video signal so that the maximum level of the sync pulses is at 100% amplitude. The brightest picture signals are in the opposite negative direction.

Negative Picture Transmission:
Transmission system used in North America and other countries in which a decrease in illumination of the original scene causes an increase in percentage of modulation of the picture carrier. When demodulated, signals with a higher modulation percentage have more positive voltages.

Noise:
An unwanted signal which interferes with reception of the desired information. Noise is often expressed in degrees Kelvin or in decibels.

Noise Figure:
The ratio of the actual noise power generated at the input of an amplifier to that which would be generated in an ideal resistor. The lower the noise figure, the better the performance.

Noise Temperature:
A measure of the amount of thermal noise present in a system or a device. The lower the noise temperature, the better the performance.

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Odd Field:
The half frame of a television scan which is composed of the odd numbered lines.

Offset Feed:
A feed which is offset from the center of a reflector for use in satellite receiving systems. This configuration does not block the dish aperture.

Packet Identity (PID):
A 13-bit number that identifies transport stream packets containing data from a single data stream

Packetizer:
An entity that breaks a stream up into discrete units of data and, usually, encapsulates each packet with extra information used to allow the packets to be reliably re-assembled into the continuous data stream

Packetized Elementary Stream (PES):
An elementary stream that is divided into typically large packets of defined structure before being further packetized for the MPEG transport process

Phase Alternate Line (PAL):
The European/African color TV format which evolved from the American NTSC standard. PAL-I version used in South Africa.

Patching:
Patching means altering the software or firmware to create new possibilities. When we talk about patching receivers (like the famous Allcam patch) it means that the original receiver firmware is modified in such a way that it is able to do more than the manufacturer intended it to do.

The Allcam patch for instance is a modification that allows you to decode multiple coding systems on just 1 CAM. Such Allcam patches are offered for several receivers, on the web.
But also creating a new language version of the receivers operating system, requires a firmware modification and would thus be called a patch.

Pay Per View:
Pay Per View (ppv) as the name implies, is a technique, used to charge a viewer only for the program he/she watches. So with ppv, whenever you want to watch a movie or sport match, you will pay for that program only.

Phase:
A measure of the relative position of a signal relative to a reference expressed in degrees.

Phase Distortion:
A distortion of the phase component of a signal. This occurs when the phase shift of an amplifier is not proportional to frequency over the design bandwidth.

Picture Detail:
The number of picture elements resolved on a television picture screen. More crisp pictures result as the number of picture elements is increased.

Polar Mount:
A dish mount that permits all satellites in the geosynchronous arc to be scanned with movement of only one axis.

Polarisation:
A characteristic of the electromagnetic wave. Four senses of polarisation, determined by the direction of the electric field, are used in satellite transmissions: horizontal; vertical; right-hand circular; and left-hand circular.

Positive Picture Phase:
Positioning of the composite video signal so that the maximum point of the sync pulses is at zero voltage. The brightest illumination is caused by the most positive voltages.

PPUA:
The PPUA or Program Provider User Address is a 4 byte long code, composed of 2 separate codes. The first 3 bytes of the PPUA are called the Shared Address, the last byte of the PPUA is the Customer Word Pointer. The PPUA is used to identify and address cards.

Preamplifier:
The first amplification stage. In a terrestrial receive system, it is the amplifier mounted adjacent to an antenna to increase a weak signal prior to its processing at the headend

Pre-emphasis:
Increases in the higher frequency components of an FM signal before transmission. Used in conjunction with the proper amount of de- emphasis at the receiver, it results in combating the higher noise detected in FM transmissions.

Pre-Enabling:
Making subscription products available on the decoding device before release into marketplace

Presentation Time Stamp (PTS):
A 33-bit field indicating when the packetised elementary stream (PES) packet should be presented to the user (90 kHz base reference)

Prime Focus Dish:
A parabolic dish having the feed/LNA assembly at the focal point directly in the front of the dish.

Provider Group & Provider ID:
A 3 byte hexadecimal number to identify a card. The first 2 bytes identify the Provider Group, the 3rd byte is the Provider ID and is either 00 or 10. So only 2 different ID's are used. Most providers are addressed using Provider ID 00. One exception is German Provider Premiere World who uses Provider ID 10.

Program Clock Reference (PCR):
A counter based on a 27 MHz time-base used to synchronize the presentation of data arriving in different data streams on the multiplex (asynchronouly). The PCR is split into two sections when supplied - 33 bits giving 1/90 kHz resolution and a 9-bit extension to fine-tune to 27 MHz

Program Map Table (PMT):
A table that identifies the data streams that comprise a service and provides other data used for decoding these services

Program Specific Information (PSI):
Information provided in a format defined by MPEG to convey the essential data a decoder must have to receive one or more services make up of elementary streams. It consists primarily of the program association table (PAT), program map table (PMT) and conditional access table (CAT), although it also introduces the network informat

Programme Stream (PS):
An MPEG 2 multiplex with variable length packets that are typically large - intended for low error rate transport media with only a single programme, for example CD-ROM ion table (NIT)

Quadrature Phase Shift Keying (QPSK):
A modulation technique used on satellite transmissions that uses phase shifts of a carrier wave to relay 4 symbols per cycle

Q Signal:
One of two color video signal components used to modulate the color subcarrier. It represents the color range from yellowish to green to magenta.

Radio Frequency (RF):
The approximately 10 kHz to 100 GHz electromagnetic band of frequencies used for man-made communication.

Raster:
The random pattern of illumination seen on a television screen when no video signal is present.

Reed Switch:
A mechanical switch which uses two thin slivers of metal in a glass tube to make and break electrical contact and thus to count pulses which are sent to the dish actuator controller. The position of the slivers of metal is governed by a magnetic field applied by a bar or other type of magnet.

Reference Signal:
A highly stable signal used as a standard against which other variable signals may be compared and adjusted.

Return Loss:
A ratio of the amount of reflected signal to the total available signal entering a device expressed in decibels.

Retrace:
The blanked-out line traced by the scanning beam of a picture tube as it travels from the end of any horizontal line to the beginning of either the next horizontal line or field.

SAS:
SAS means subscriber authorization system. The SAS translates the subscriber information into EMM's. Also the SAS ensures that the necessary authorization is available to view a certain channel or program.

Satellite Receiver:
The indoors electronic component of an earth station which downconverts, processes and prepares satellite signals for viewing or listening.

SAW Filter:
A solid state filter that yields a sharp transition between regions of transmitted and attenuated frequencies.

Scanning:
The organized process of moving the electron beam in a television picture tube so an entire scene is drawn as a sequential series of horizontal lines connected by horizontal and vertical retraces.

Scrambling:
A method of altering the identity of a video or audio signal so it cannot be received intelligibly in order to prevent its reception by persons not having authorized decoders.

Screening:
A metal, concrete or natural material that screens out unwanted TI from entering a dish or a metal shield that prevents the ingress of unwanted RF signals in an electronic circuit.

SECA:
Société Européenne de Contrôle d'Accès (SECA), see Aston Seca.

Section:
A portion of a table that conforms to the MPEG defined syntex

Serrated Vertical Pulse:
The television vertical sync pulse which is subdivided into six serrations. These sub-pulses occur at twice the horizontal scanning frequency.

Service:
Also called a channel (for instance Eurosport), to which a TV or decoder is tuned. A Service Provider offers one or more services and negotiates with the SMS Operator to market his services as one or more products

Service Provider:
The company or institution that provides one or more services like for instance broadcasting satellite television.

Servo Hunting:
An oscillatory searching of the feedhorn probe when use of inadequate gauge control cables results in insufficient voltage at the feedhorn.

Shared Address:
The Shared Address (SA) are the first 3 bytes of the PPUA and is used to address cards groupwise. A card group can contain a maximum of 256 individual cards.

Side Lobe:
A parameter used to describe the ability of a dish to detect off-axis signals. The larger the side lobes, the more noise and interference a dish can detect.

Single Channel Per Carrier (SCPC):
A satellite transmission system that employs a separate carrier for each channel, as opposed to frequency division multiplexing that combines many channels on a single carrier.

Signal Dropout:
The loss of signal that occurs when the signal becomes too weak to be usable

Signal-to-Noise Ratio:
S/N - The ratio of signal power to noise power in a specified bandwidth, usually expressed in decibels

Signature:
The signature (the authentication code) is a 5 byte hexadecimal code and is used to secure the data stream. The signature is a kind of checksum control for the data stream.

Skew:
A term used to describe the adjustment necessary to fine tune the feed polarity detector when scanning between satellites.

Smart card:
A Chipcardcontaining a processor and some memory. The memory on the card can be altered either by software on a PC and using a programmer as an interface to the card, or it can be altered by the CAM/receiver by means of instructions which are contained in the data stream of the satellite signal.

Subsciber Management System (SMS):
SMS or subscriber management system. The SMS is a subsystem of the CA.It manages the information about a subscriber (such as number, names, addresses, telephone numbers, etc... ) and requests EMM'sfrom the SAS.

SMS-Operator/Provider:
The SMS Operator manages customers who subscribe to one or more services. The Service Provider requests that the SMS Operator manages and gather subscription fees from his subscribers and also perform other tasks

Snow:
Video noise or sparklies caused by an insufficient signal- to-noise input ratio to a television set or monitor. r subscriber-related tasks

Solar Outage:
The loss of reception that occurs when the sun is positioned directly behind a target satellite. When this occurs, solar noise drowns out the satellite signal and reception is lost.

Sparklies:
Small black and/or white dashes in a television picture indicating an insufficient signal-to-noise ratio. Also known as snow.

Spherical Dish:
A dish system using a section of a spherical reflector to focus one or more satellite signals to one or a series of focal areas.

Splitter:
A device that takes a signal and splits it into two or more identical but lower power signals.

Subcarrier:
A signal that is transmitted within the bandwidth of a stronger signal. In satellite transmissions a 6.8 MHz audio subcarrier is often used to modulate the C-band carrier.

Surface Acoustic Wave (SAW):
A sound or acoustic wave traveling on the surface of the optically polished surface of a piezoelectric material. This wave travels at the speed of sound but can pass frequencies as high as several gigahertz.

SMATV:

Synchronizing Pulses:
Pulses imposed on the composite baseband video signal used to keep the television picture scanning in perfect step with the scanning at the television camera. See SAW Filter.

Table:
An MPEG structure that can be updated in sections and which can contain any of a variety of data

Thermal Noise:
Random, undesired electrical signals caused by molecular motion, known more familiarly as noise.

Time-Shifted Event:
The same program broadcast on two or more channels, each broadcast starting a fixed period of time after the previous one. This is mainly intended for PPV. For example, the same movie can be started on nine different channels, each delay 10 minutes from the previous one. A subscriber then has to wait a maximum of 10 minutes for the start of this movie. The fact that the same movie is transmitted more tha

Trace:
The movement of the electron beam from left to right on a television screen. n once is usually transparent to the subscriber.

Threshold:
A minimal signal to noise input required to allow a satellite receiver to deliver an acceptable picture.

Transponder:
One circuit on a satellite that receives, modulates, amplifiers and re-transmits an uplinked signal

Transport Stream:
An MPEG-2 multiplex with short, fixed-length packets carrying many programs intended for general broadcast over potentially error-prone media, such as a satellite broadcast.

Trap:
An electronic device that attenuates a selected band of frequencies in a signal. Also known as a notch filter.

UART:
Short for Universal Asynchronous Receiver-Transmitter. The UART is a computer component that handles asynchronous serial communication. Every computer contains a UART to manage the serial ports.

UHF:
Ultrahigh frequencies ranging from 300 to 3,000 MHz. North American TV channels 14 through 83. African and European TV channels 21 to 69.

Upconverter:
A device that increases the frequency of a transmitted signal.

Uplink:
The earth station electronics and antenna which transmit information to a communication satellite.

Vertical Blanking Pulse:
A pulse used during the vertical retrace period at the end of each scanning field to extinguish illumination from the electron beam.

Vertical Sync Pulse:
A series of pulses which occur during the vertical blanking interval to synchronize the scanning process at the television with that created at the studio. See also Serrated Vertical Pulse

VHF:
Very high frequencies. The lower frequency range for terrestrial television broadcasts.

Viaccess:
A coding system which is gaining increased popularity among providers lately. Viaccess is widely used in France and by several providers in the north east of Europe. It is a relative newcomer.

Videoguard:
A coding system that is used by English based Sky Television mainly.

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What is MPEG?
MPEG stands for Moving Picture Experts Group. It is a standard method of transmitting digital video and sound in a compressed format using less bandwidth than the traditional analog method.
The first MPEG standard introduced was MPEG-1 which is used to compress film onto regular compact discs (VideoCDs). MPEG-1 uses a low bit rate resulting in a picture similar to VHS video tape. The MPEG-1 data stream supports only one video signal and is therefore not used for satellite transmissions. MPEG-1 uses either 25 or 30 frames per second and is therefore not very well suited to storage of interlaced video.
Broadcasters wanted the enconomy of digital transmission, but because MPEG-1 was not suitable for satellite and MPEG-2 was still being developed, a "bastardized" flavor of MPEG which I call MPEG-1.5 was created. This format is not a official standard, but is still used for satellite (CNN Airport network uses MPEG-1.5). MPEG-1.5 uses a wide bandwidth MPEG-1 flavor of video encoding along with multiplexing of data streams which allows multiple programs to be transmitted across one satellite channel at a time.
MPEG-2 is becoming the de-facto standard in the digital TV world. MPEG-2 fixes many of the problem inherent in MPEG-1, such as resolution, scalability and handling of interlaced video. It allows for a much better picture (studio quality and up to HDTV levels) and allows multiple channels at various bitrates to be multiplexed into a single data stream. It was officially adopted by ISO and has the catalog number ISO 13818-1.
Program producers (like NBC, HBO et al) prefer to use MPEG-2 to distribute their programming because they can transmit multiple programs in the same space as a single analog transmission. Satellite and cable companies also like the idea of digital compression and it allows them to offer much more programming versus analog with the same amount of bandwidth. All licensed US DBS providers (DirecTV, USSB, Echostar etc.) are required by their licenses to transmit in digital format.
What is DVB?
DVB stands for Digital Video Broadcast and is a standard based upon MPEG-2 video and audio. DVB covers how MPEG-2 signals are transmitted via satellite, cable and terrestrial broadcast channels along with how such items as system information and the program guide are transmitted along with the scrambling system used to protect the signal.
With the exception of the United States of America, Mexico, Canada, South Korea and Taiwan, DVB has been adopted by just about every country in the world for digital TV & radio. This document concentrates on DVB-S, the satellite format of DVB - DVB-C is the specification for DVB/MPEG-2 over cable and DVB-T is DVB/MPEG-2 over terrestrial transmitters.
What is Digicipher?
Please see our new section on DCII
What is ATSC?
ATSC is Advanced Television Systems Committee which is destined to replace NTSC as the method of terrestrial television transmissions in the United States, Canada, Mexico, South Korea and Taiwan. Like DCII, ACTS uses the MPEG-2 video specification, but bastardizes everything else, making North American (and South Korea/Taiwan) an island in a world of standards.
ATSC is almost exactly the same as Digcipher 2 and of course it's no surprise that General Instrument was on the comitee that recommended ATSC to the FCC. In theory, ATSC and Digicipher 2 have a couple of advantages over MPEG-2/DVB, especially in the area of signal aquisition time, however, this is not enough to justifying a totally different standard than the rest of the world.
An interesting tidbit about why ATSC uses AC3 for audio and not Musicam recently surfaced. In the field trials during the development of the ATSC specification, both AC3 and Musicam were tested. Technically both have the same merits, including the ability to do 5.1 audio in the same bandwidth. However, AC3 was chosen because in one area, it was tested to have better performance than Musicam. It was later discovered that the testing procedure was flawed and that subsequent re-testing after the standard was published showed that AC3 and Musicam performed equally as well.
Like DVB/MPEG-2, ATSC supports HDTV.
Will there ever be a receiver than can do ATSC, DCII and MPEG-2/DVB?
Yes - Motorola's DSR-4800 receiver is able to process both DVB and DCII formats, however, it's worth pointing out that this is a commercial receiver with a $4,000 price tag.
Obviously, because of the differences in audio encoding, the receiver handles both AC3 and MPEG-1, as the second generation of MPEG-2/DVB silicon is now coming onto the market has the capability to do both audio standards.
Additionally, because DCII and ATSC are so similar, the DCII specification is now 95% public information, whereas in the past it was considered proprietary to General Instrument. In a complete turn about, GI now licenses the DCII specification and has recently signed a cross license agreement with Scientific Atlanta, one of the early adoptors of the MPEG-2/DVB standard.
Symbol Rates, FEC and that kinda stuff
What's a symbol?
Like just about any form of digital transmission, the receiver has to know the rate at which the transmitter is sending information. In the computer world, we call this the bit rate. For example, PCs can transmit from their serial ports at up to 115,200 bits per second. Bit rate and baud rate are not the same, despite the fact that some people will turn blue trying to tell you that they are. The bit rate specifies how many bits per second are carried across the channel (phone line, serial cable or satellite transponder), however, the baud rate describes the rate that data is sent within the channel.
For example, suppose you invented a simple modem that transmitted at 50 bps by using two tones. One tone could signal a 1 needed to be sent and the other would signal 0. Now imagine that you wanted to double the transfer rate across the channel. By using four tones instead of two, you could signal two sets of bits at the same time by switching various combinations of the four tones. The baud rate is still 50 baud (i.e. the tone pairs change 50 times per second), however, the bit rate is now 100 bps. The combination of the sets of tones is called a "symbol" because too many people are confused by the term baud.
What's QPSK modulation?
When satellite transponders are used to transmit MPEG-2 signals, Quadrature Phase Shift Keying is used to modulate the digital information onto an RF carrier.
Rather than using the amplitude or frequency of the carrier to convey the information, QPSK modulates the phase of the carrier signal. Depending on the data being modulated, the carrier is forced into one of four different phase states, known as a symbol. The great advantage of this method is that each symbol contains two data bits, thus doubling the potential amount of data that is transmitted over conventional amplitude or frequency modulation (AM or FM) techniques.
The diagrams below illustrate a typical implementation of QPSK:

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Figure 1 shows each possible pair of data bits is represented by a different phase angle and figure 2 shows and example of a QPSK waveform.
Because of QPSK, data rates are quoted in Symbol Rate rather than bit rate. In the case of QPSK modulation, the bit rate is twice high as the symbol rate. For example an SR of 20MS/s (20 mega-symbols) means 40Mb/s (40 mega-bits bits per second).
What's FEC?
Satellite transponders are rather noisy communications channels are are therefore subject to a large number of errors when a signal is sent through them. Because satellite transmissions are broadcast, the receiver cannot send a message to the transmitter to say "I didn't get that last piece of information, please re-transmit it". As a result, Forward Error Correction is used, where the transmitter sends error correction information along with the actual signal so that should errors occur, the receiver can re-generate the bit stream.
FEC when used with QPSK modulation uses two forms of error correction. The first, called convolutional coding with the Viterbi algorithm code is quoted as a fraction, for example, 2/3. The fraction defines the amount of the symbol rate that's used for real data, with the remainder used error correction purposes.
After the convolutional error correction code has been removed and used as needed, a second error form of error correction is used called the Reed-Solomon code. This correction results in 188 bytes out for every 204 bytes coming in with the remainder used as parity bits to help correct any remaining errors. Additionally, the FEC scheme also uses interleaving of the data stream to prevent noise bursts from interrupting the flow of data in much the same way that CDs use it to prevent scratches from causing drop-outs.
Consider the following message:
This is a sample message If interleaved, it might look like:
eTs haais mgi smeaesp l Should an error occur and say wipe out the 'mgi' part of the message, the de-interleaved message will now read
This *s a sa*ple messsa*e As a result, only single characters are missing from the message (shown here as asterix), rather than an entire word missing in the case of non-interleaved data.
As a final step, the QPSK symbols are scrambled to ensure that long runs of the same symbol value don't cause a lack of change in phase of the carrier. Since the QPSK demodulator obtains its signal clock from directly from the signal, there must be a large number of phase changes in order to re-generate the clock and of course scrambling results in this. Note: this form of scrambling is not the same as scrambling of the decoded signal.
Why use different SR/FEC values?
When people purchase time on a satellite, in effect they are primarily paying for the bandwidth. Therefore if a programmer wanted to transmit three video channels via a transponder, he would use less bandwidth than a service that transmitted six. However, the bandwidth of a transponder is finite and therefore an upper limit is placed on the SR (typically between 28 and 29 MS/s). By reducing the amount of FEC information sent along with the actual data, the number of channels can be increased. However, this then means that errors are harder to correct and that the down link stations must be able to receive a certain signal strength (i.e. use a certain size dish) in order to receive quality programming via the transponder.
What's QAM and Vestigal Sideband?
Quadrature Amplitude Modulation is the cable version of QPSK. Using many different symbol phases (the initial standard for the US is 64 different phases), a given 6MHz of cable bandwidth will be able to carry the same amount of data as a single 30MHz transponder. Given a 125 channel cable system, this means that they will be able to carry 625 video and audio programs assuming compression levels where five video services are sent on a single RF channel.
Vestigal Sideband modulation (otherwise known as VSB-8) is the technique that will be used in the US for terrestrial ATSC transmission. VSB-8 uses AM transmission with phase information within the sideband. The other sideband is almost totally surpressed and a pilot carrier is inserted to help receivers initially acquire the signal. VSB-8 uses eight phases with 3 bits encoded per phase which are then reduced to two bits in the receiver. I could try to explain how it works, but Harris Semiconductor has written a much better explanation which is linked at the bottom of this page.
How do I make sense of the SR/FEC/PID listings on the Lyngsat Chart?
If you've seen something like:
12,177 V SR 23000 FEC 2/3
V 0FF0 A 0100 ATN
V 0FF1 A 0101 RTN
V 0FF3 A 0103 HealthSouth
V 0FF4 A 0104 RE/MAX TV
This means that the transmission is centered at 12.177 GHz, uses Vertical polarity for the down link, uses a symbol rate of 23.000 MS/s and FEC of 2/3. This is a multi-channel package that contains four video services with the Video and Audio PIDs for the individual packages listed. The PIDs are shown in hexadecimal format.


SCPC, MCPC, PIDs and Formats What's MCPC?
MCPC stands for Multiple Channel Per Carrier. Given an average satellite transponder with a bandwidth of 27MHz, typically, the highest symbol rate that can be used is SR 26MS/s. Obviously, with this large bandwidth, multiple video or audio channels can be transmitted via the transponder at the same time.
MCPC uses a technique called Time Division Multiplex to transmit the multiple programs at the same time. As one can expect from the name, TDM sends data for one channel at a certain time and then data for another channel at another time.
Many encoder manufacturers are currently experimenting with statistical multiplexing of MPEG-2 data. Using this technique, channels that need high data rate bursts in order to prevent pixelization of the picture (such as live sports events), will obtain the bandwidth as they need it by reducing the data rate for other services that don't.
Statistical multiplexing should improve perceived picture quality, epecially on video that changes rapidly and has the advtange of requiring no changes in the receiver equipment.
What's SCPC?
SCPC stands for Single Channel Per Carrier. In the case of this type of transmission, only a part of the available transponder is used for the signal. The satellite operator can sell the remaining space on the transponder to other up linkers. SCPC is typically used for feeds rather than for direct programming. SCPC has the advantage over MCPC that the signals up linked to the same transponder can be transmitted up to the satellite from different locations (SNG trucks for example), but has the disadvantage of not being quite as efficient as MCPC because of "guard bands" which keep the SCPC signals on the same transponder separated from each other.
NBC uses SCPC MPEG-2 for its back haul feeds and is able to use up to four SCPC transmissions on a single satellite transponder (GE-1 Ku-Band). Microspace uses the same type of transponder on the same satellite, but in MCPC format and is able to transmit six video channels and a few audio channels in the same space.

[gessle]

Sistemul solar, Planetele si satelitii lor, Planete telurice, Planetele indepartate


Universul
Universul reprezinta totalitatea de energie si materie, inclusiv Pamantul, galaxiile si continutul intergalactic.
Soarele 28834vgf78gni6y
Datorita faptului ca se afla atat de aproape, Soarele 28834vgf78gni6y este steaua cea mai bine cunoscuta.

Astronomii disting chiar detaliile de la suprafata sa ( cele mai mici au o intindere de 150 km ). In comparatie cu Pamantul Soarele 28834vgf78gni6y este gigantic, volumul sau ar putea cuprinde 1 300 000 de planete ca a noastra, iar de alungul diametrului sau s-ar putea alinia la 109. Soarele 28834vgf78gni6y
este o imensa sfera de gaz foarte cald a carui masa o depaseste de gn834v8278gnni
300 000 de ori pe cea a Pamantului. La suprafata forta gravitationala
este de aproximativ 28 de ori mai puternica de cat cea de pe Pamant,
totusi Soarele 28834vgf78gni6y nu e decat o stea foarte obisnuita. Pentru astronomi, este
o adevarata sansa sa poata studia o stea atat de banala, tot ceea ce afla prin studierea Soarelui ii ajuta sa inteleaga mai bine si celelalte stele.

Fotosfera

Lumina orbitoare a Soarelui provine de la un invelis de grosime mai mica de 300 km, fotosfera. Aceasta este cea care da impresia ca Soarele 28834vgf78gni6y are o margine bine delimitata, temperatura sa este de aproximativ 6000 grade C. Vazuta prin telescop ea se prezinta ca o retea de celule mici stralucitoare, sau granule, eflate intr-o permanenta miscare. Ficare granula este o bula de gaz de marimea unei tari ca Franta, ea apare se transforma si dispare in aproximativ 10 minute.


Planetele si satelitii lor
Cele 9 planete principale ale sistemului solar se invartesc in jurul Soarelui in sensul acelor de ceasornic , la distante cuprinse intre minimum 45.9 milioane de km in cazul planetei Mercur si maximum 7.4 miliarde de km in cazul planetei Pluto . Planetele telurice sunt cele mai apropiate de Soare . Planetele gigant se afla mai departe iar si mai departe , planetele indepartate .
Mercur , Venus , Pamant si Marte , cele patru planete situate cel mai aproape de Soare sunt planetele telurice : ele sunt alcatuite din roci destul de dense . Suprafata lor - numita crusta sau scoarta – este solida . Ele sunt de talie mijlocie : diametrul lor este pana la 5000 km in cazul celei mai mici (Mercur) si sub 13000 in cazul celei mai mari (Pamantul) . Aceste planete au evoluat mult de cand s-au format . Ele au pierdut invelisul initial de gaz usor , iar atmosfera lor actuala provine de la gazul din interiorul acestor planete . Relieful lor s-a modificat pe parcursul timpului .
Planetele gigant , situate dincolo de Marte , Jupiter si Saturn sunt mai voluminoase decat planetele telurice . Ele reprezinta adevarte planete gigant . Diametrul lui Jupiter este de aproape 11 ori mai mare decat cel al Pamantului ; cel al lui Saturn de 9 ori mai mare . Dar densitatea lor este mult mai mica : aceste planete sunt in esenta sfere de gaz . Aceste planete nu au o suprafata solida ci doar un nucleu de roci si gheata . Ele au evoluat putin de cand s-au format si si-au pastrat invelisul initial : o atmosfera densa pe baza de hidrogen si heliu ( doua gaze usoare ) . Au o miscare rapida de rotatie ( in 10 pana la 16 h ) si sunt inconjurate de inele de materie .
Dupa Jupiter si Saturn urmeaza cele trei planete care sunt cel mai departe de Soare : Uranus , Neptun , si Pluto . Uranus si Neptun nu sunt atat de mari ca Jupiter . Ele sunt formate in principal din gaze usoare si sunt inconjurate de inele . Se crede ca interiroul lor contine o cantitate insemnata de gheata . Pluto , cea mai indepartata este un caz aparte : ea se aseamana planetelor telurice prin dimensiunea ei mica (un diametru de 2300 km ) si planetelor mari prin densitate scazuta . Cu exceptia lui Mercur si a lui Venus , principalele planete ale sistemului solar au unul sau mai multi sateliti . Astazi se cunosc in total 61 . Dintre acestia 27 au fost descoperiti datorita fotografiilor realizate de sondele spatiale . In functie de dimensiune satelitii pot fi clasificati in trei categorii . Cei mai mari sunt Luna , cei patru sateliti ai lui Jupiter ( Io , Europa , Ganimede si Calisto ) , satelitul cel mai mare al lui Saturn (Titan) si principalul satelit al lui Neptun (Triton) . Ei au un diametru de peste 3000 de km . Unii ca Luna si Calisto sunt formati din roci ; altii dintr-un amestec de gheata si roci . Satelitii de dimensiuni mijlocii au un diametru intre 200 si 1600 km . Ei se afla in jurul planetelor Saturn , Uranus , Neptun si Pluto . Majoritatea sunt formati dintr-un amestec de gheata si roci . In sfarsit minisatelitii , cu forma neregulata si o marime mai mica de 200 km ( cei mai mici chiar de cativa km ) , constituie a treia categorie . Cei mai cunoscuti sunt cei doi sateliti ai planetei Marte : Phobos si Deimos

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Planete telurice
Chiar daca la prima vedere cele 4 planete telurice ( Mercur , Venus , Pamantul si Marte ) sunt diferite , ele se aseamana prin dimensiuni si structura . Inca de la inceputul anilor ’60 , sondele spatiale au fost trimise spre Venus si Marte pentru a le studia .
Terra
Pamantul se afla la aproximativ 150 de milioane de km de Soare . El efectueaza miscarea de revolutie in aproape 365.25 zile , iar cea de rotatie in jurul propriei sale axe in 23h 56min 4sec . Aceasta este cea mai voluminoasa dintre cele patru planete telurice : ea are un diametru putin mai mare de 12700 km . In jurul Pamantului se afla aer , un amestec de gaz continand 78% azot si 21% oxigen . Specificul Pamantului consta in faptul ca este singura planeta pe care apa poate ramane lichida , favorizand astfel aparitia si dezvoltarea vietii . Aceasta apa , care erodeaza treptat rocile contribuie si la modificarea reliefului pe suprafata terestra. Temperatura cea mai ridicata pe Pamant este de +58 grade in Libia , iar cea mai scazuta de –89.9 grade in Antarctica . Pamantul are un singur satelit: Luna.
Luna

• Diametrul este de 3476 km
• Masa de 81,3 ori mai mica decat a Pamantului
• Volumul de 50 ori mai mic decat al Pamantului
• Departarea fata de Pamant este de 356400 km la pigeu si 406700 km la apogeu
• Densitatea: 3,34 g/cm3
• Atmosfera este practic absenta
• Temperatura circa 150 grade C pe partea insorita si 1380 pe partea umbrita
• Perioada de revolutie (in jurul Pamantului) este egala cu perioa-da de rotatie (in jurul axei sale) ca urmare are indepartata me-reu aceasi emisfera catre Pamant.
• Aselenizarea primilor pamanteni a avut loc la 21 iulie 1969
• Regiunile plate mai intense poarta numele de “mari” si “oceane” (Marea Linistei, Oceanul Furtunilor) si sunt delimitate de lanturi muntoase cu denumiri similare celor de pe Pamant (Alpi, Caucaz, Carpati).

Mercur
Mercur se afla la 58 milioane de km de Soare si face inconjurul acestuia in 88 de zile . Cum aceasta planeta este situata aproape de Soare si se invarteste lent in jurul propriei sale axe ziua este foarte cald (pana la 400 de grade) , iar noaptea foarte frig . Aceasta este cea mai mica dintre planetele telurice ( 4880 km in diametru ) . Mercur este practic lipsit de atmosfera pentru ca la fel ca Luna nu este suficient de greu pentru a retine un invelis de gaz . Absenta atmosferei a facut ca , pe parcursul a miliarde de ani , sa fie lovit de mici corpuri care circulau in spatiu . Mercur nu are nici un satelit cunoscut .
Venus

Situata la 108 milioane km de Soare , Venus isi parcurge orbita in 225 de zile . Rotatia in jurul propriei sale axe este foarte lenta , dureaza 243 de zile si are loc de la est la vest , in sens invers fata de rotatia celorlalte planete . Cu un diametru de 12100 km Venus este cu foarte putin mai mica decat Pamantul , dar atmosfera sa este foarte diferita : in principal aceasta este compusa din 96% gaz carbonic si 3.5% azot . Este inconjurata de un val gros de nori repartizati in 3 straturi situate la o altitudine intre 50 si 70 km . Unii dintre acestia provoaca ploi de acid sulfuric , o substanta chimica foarte periculoasa . Pe Venus temperatura este foarte ridicata . De fapt , gazul carbonic acumulat in atmosfera actioneaza sub efectul razelor Soarelui ca geamurile unei sere : temperatura la sol ajunge pana la 460 grade . Suprafata lui Venus este plina de platouri vulcanice . Se pare ca multi vulcani sunt inca activi . La fel ca Mercur , Venus nu are sateliti .

Marte
Planeta Marte este situata la aproximativ 228 milioane km de Soare . Ea inconjoara Soarele 28834vgf78gni6y in 687 de zile si se invarteste in jurul propriei sale axe in 24 h 37 min . Diametrul sau (6800 km) reprezinta putin mai mult decat jumatate din diametrul Pamantului . Din cauza slabei ponderabilitati ( o treime din cea a Pamantului ) ea nu a mai putut retine decat un invelis atmosferic neinsemnat . Acesta contine 95.6% gaz carbonic , 2.7% azot , 1.6% argon si urme de oxigen . Fiind mai departe de Soare decat Pamantul , Marte este o planeta mai rece : temperatura la sol scade in mod curent la –50 grade si nu depaseste niciodata 20 de grade . La fel ca Venus Marte pastreaza urmele unei intense activitati vulcanice : aici pot fi observati cei mai mari vulcani ai sistemului solar , cu o inaltime de peste 20 km . Suprafata desertica si stancoasa prezinta o frumoasa culoare rosiatica . De fapt rocile contin un oxid de fier care le da o culoare oarecum asemanatoare cu cea a ruginei . Uneori au loc furtuni violente care ridica nori de praf . In jurul lui Marte se invartesc doi sateliti de dimensiuni mici : Phobos si Deimos .

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Planetele gigant
Dincolo de Marte se afla doua planete gigant : Jupiter si Saturn . Usor vizibile si cu ochiul liber , ele au fost urmarite inca din antichitate . Cele mai concrete informatii in privinta lor au fost furnizate de sondele americane Voyager care le-au survolat intre 1979-1981 . Spre deosebire de Pamant , Jupiter si Saturn nu au o suprafata solida : aceste doua planete sunt doua imense sfere de gaz .
Jupiter
Jupiter este cea mai mare dinte toate planetele sistemului solar : are un diametru de 11 ori mai mare decat cel al Pamantului , o masa de 318 ori mai mare si un volum de 1300 de ori mai mare . Jupiter se afla la 778 milioane km de Soare . Acest gigant este inconjurat de o atmosfera densa pe baza de hidrogen si heliu , in care circula nori formati tot din gaze solidificate sau lichefiate : in special metan si amoniac . Cum el se invarteste foarte repede in jurul propriei sale axe ( mai putin de 10 h ) acesti nori se intind la ecuator si il acopera ca niste brauri . Norii aflati la exteior au aspect stralucitor , ceilalti , in schimb , sunt intunecati . Aceste formatiuni noroase sunt foarte turbulente : s-au observat turbioane enorme , care se modifica mai mult sau mai putin rapid . Unele dintre ele formeaza o imensa pata rosie , care i-a intrigat mult timp pe astronomi : este un uragan permanent , de patru ori mai mare decat Pamantul . Nivelul superior al norilor este foarte rece ( -148 grade ) , dar cu cat se coboara spre interiorul planetei , temperatura si presiunea cresc . In centrul lui Jupiter , temperatura atinge 30000 grade iar presiunea de 100 de milioane de ori mai mare decat la suprafata Pamantului . Jupiter are 16 sateliti cunoscuti . Patru dintre acestia sunt sateliti mari , cu o talie comparabila cu cea a lunii : Io , Europa , Ganimede si Callisto . Ceilalti sunt sateliti , cu un diametru de cateva zeci de kilometri . Sondele americane Voyager au produs o adevarata surpriza dezvaluind faptul ca pe Io , unul din cei patru sateliti principali ai lui Jupiter , exista numerosi vulcani activi , chiar daca suprafata sa este inghetata . Atrasa , pe de-o parte de planeta gigant Jupiter si , pe de alta de trei sateliti mari ai acestei planete materia situata in interiorul satelitului Io este in permanenta deformata si incalzita . Ea tasneste periodic la suprafata prin niste vulcani mari , cum este vulcanul Pele . Uneori lava de sulf este aruncata cu peste 3000 km/h la o inaltime mai mare de 200 km.

Inelele lui Jupiter
Sunt mai putin spectaculoase decat cele ale lui Saturn . Inelul principal are marginea exterioara la aproximativ 57000 kmde cei mai inalti nori ai atmosferei . Cu o inaltime de aproximativ 6000 km , el se prelungeste spre planeta intr-un halo difuz si , in partea opusa printr-un inel exterior mare
Saturn
Alt gigant , Saturn , are un diametru de 9,5 ori mai mare decat cel al Pamantului , de 95 de ori masa acestuia si de 750 de ori volumul lui . Saturn este situat la 1,4 miliarde de kilometri de Soare . La fel ca Jupiter , acesta este o sfera gazoasa care se invirteste foarte repede in jurul propriei sale axe ( in putin mai mult de 10 ore ) . Dar Saturn este mai putin des deoarece contine mai mult hidrogen : Saturn ar putea sa pluteasca pe apa ! Norii care il inconjoara sunt animati de miscari foarte violente : adevarate cicloane . La fel ca Jupiter , Saturn are o sursa de caldura interna : el emite aproape de trei ori mai multa enrgie decat cea primita de la Soare . In jurul lui Saturn s-au descoperit 18 sateliti , printre care unul gigantic numit Titan , mai mare decat planeta Mercur .
Inelele lui Saturn
Marea particularitate a lui Saturn consta in sistemul de inele care il inconjoara ; acesta este atat de amplu incat poate fi perceput chiar si cu o luneta de amatori . Galileo Galilei il intrezareste inca din 1612 , dar abia olandezul Huygens va fi cel care va intelege pentru prima oara fenomenul , in 1659 . De pe Pamant nu s-u descoperit decat sase inele , dar fotografiile realizate de sonda Voyajer au demonstrat ca ele sunt de ordinul miilor . Ele formeaza in jurul lui Saturn , in planul ecuatorului sau , un fel de disc imens , cu diametrul de 300000 km , dar cu o grosime de numai un kilometru . Dupa pozitia lui Saturn in functie de pamint si de soare , noi vedem aceste inele mai mult sau mai putin inclinate . Atunci cand ele apar pe muchie sunt atat de subtiri incit nu le mai vedem . Aceste inele sunt alcatuite din blocuri de gheata si pulberi care seinvirt in jurul planetei ca niste sateliti mici .

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Planetele indepartate
Dincolo de planetele gigant au fost descoperite alte planete de mari dimensiuni : Uranus si Neptun . Foarte indepartate , aceste planete sunt greu de studiat de pe Pamant . Ele sunt cunoscute mai bine de cand au fost survolate de sonda americana Voyajer 2 : Uranus in 1986 , Neptun in 1989 . In privinta lui Pluto , de acesta nu s-a apropiat nici o sonda spatiala , raminind astfel destul de misterioasa.
Uranus

In 1781 , Uranus a fost observat prin telescop din intamplare de catre astronomul englez William Herschel , care a crezot la inceput ca este o cometa . El are de 4 ori masa pamintului si de 15 ori masa acestuia . Se afla la 2,8 miliarde de km de soare . Mai mic si mai dens decat Jupiter si Saturn , Uranus este inconjurat la fel ca acestia de o atmosfera densa , pe baza de hidrogen si heliu . Insa atmosfera lui contine si un gaz care ii da o frumoasa culoare albastra : metan . Uranus este un adevarat ghetar : temperatura lui coboara sub –200 grade . Se crede ca nu contine hidrogen lichid metalic ci un nucleu de roci acoperit de un invelis dens de gheata . El este inconjurat de 10 inele de pulberi intunecate , care se desfasoara la o distanta intre 42000 si 51000 km de centrul planetei . In jurul lui Uranus au fost reperati 15 sateiti : cei mai mari , in numar de 5 au fost observati de pe Pamant , ceilalti au fost descoperiti de catre sonda Voyajer 2 .
Neptun
Neptun a fost descoperit in anul 1846 , chiar in locul in care astronomul francez Urbain Le Verrier a calculat ca ar trebui sa se afle , fiindca numai prezenta sa putea explica anumite anomalii ale miscarilorlui Uranus . Neptun se afla la o distanta medie de 4,5 miliarde de km de Soare . Prin aspectul talia si masa sa , Neptun este o adevarata sosie a lui Uranus , dar atmosfera lui estemai agitata . La diferite altitudini s-au observat nori deplasati de vanturi de peste 1000 km/h . Formatiunea cea mai spectaculoasa este o pata mare , intunecata , de marimea Pamantului . Ea aminteste de marea pata rosie a lui Jupiter . Aceasta este un uragan enorm , al carui turbion are peste 600 km/h . La altitudine mai mare circula nori luminosi , foarte rapizi , formati fara indoiala din cristale de gheata di metan . Din cauza indepartarii mari fata de Soare , Neptun primeste de 900 de ori mai putina enrgie solara decat Pamantul . In acelasi timp , s-a constatat ca el emite de 2,7 ori mai multa energie decat primeste . Nu se cunoaste sursa acestei calduri interne , dar ea explica vilentele miscari ale atmosferei . Datorita lui Voyajer 2 , au fost identificate in jurul lui Neptun 3 inele cufundate intr-un disc de pulberi ; particularitatea celui din exterior este aceea ca reprezinta 3 arcuri mai conturate , de-a lungul carora exista mai multa materie . Neptun are 8 sateliti cunoscuti . Cel mai mare , Triton , este corpul cel mai rece observat vreodata in sistemul solar . Temperatura la sol este de –228 grade .
Pluto
Cand a fost descoperi , in 1930 , Pluto era cea mai indepartata planeta din sistemul solar . Dar , cum orbita sa are forma unei elipse foarte alungite , distanta de soare variaza intre 4,4 si 7,4 miliarde de km . Astfel , din 1979 , Pluto se afla mai aproape de Soare decat Neptun iar acest lucru a durat pana in martie 1999 . Cu un diametru mai mic de 2500 km , el este de proportii mai reduse decat Luna . Vazut de pe Pamant , dimensiunile sale sunt echivalente cu cele ale unei monede vazute de la o distanta de zeci de km ! Nu a fost survolat de nici o sonda si ramane prea putin cunoscut . Se crede ca este format dintr-un nucleu de roci , inconjurat de un invelis de gheata . Suprafata sa ar putea fi acoperite cu azot si metan inghetate . Planeta ar avea o atmosfera rarefiata care contine metan . Unii cred ca aceasta planeta este un fost satelit al lui Neptun . Ea ar fi devenit libera I urma coliziunii cu un alt corp . In 1978 i s-a descoperit un satelit : Charon . Diametrul sau , de ordinul a 1200 km , reprezinta aproape jumatate din cel al lui Pluto . In sistemul solar , nu exista alte exemple de satelit proportional atat de mare in raport cu planeta sa .
Viitorul sistemului solar
Sistemul solar este menit sa dispara . De fapt , de cand Soarele a inceput sa straluceasca energia sa (lumina si caldura) rezulta din reactiile nucleare care transforma hidrogenul intr-un gaz ceva mai greu , heliul . Dar in mai putin de 5 miliarde de ani tot hidrogenul aflat in centrul sau va disparea . Noi fenomene se vor declansa si Soarele va creste in dimensiuni : se va transforma intr-o stea gigantica rosie . Pamantul va deveni atunci un adevarat cuptor : temperatura de la suprafata va atinge in jur de 2000 grade Celsius si din aceasta cauza rocile se vor transforma in roca fierbinte ! Cu mult inainte de acestea oceanele vor fi secat si intreaga viata va fi disparut . Dupa ultimele tresariri , Soarele 28834vgf78gni6y va inceta sa mai creasca . Materia se va contracta pentru a da nastere unei stele mici , de dimensiune Pamantului , dar cu o densitate deosebita ; o pitica alba care se va stinge treptat lasand sistemul solar in frig si intuneric .
Spectroscopia a dat informatii despre compozitia chimica si miscarea obiectelor astronomice. De-a lungul lungul secolului 20 constrirea unor telescoape din ce in ce mai mari a permis cunoasterea structurii galaxiilor si a unor parti din galaxii. Au fost construite clase noi de echipament astronomic sensibil la variatia radiatiilor electromagnetice.

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TELEVIZIUNEA PRIN SATELIT

Televiziunea prin satelit se foloseste de sateliti situati pe orbite eliptice (cu un tur complet de circa 12 ore) sau geostationare, dotati cu antene parabolice mari (diametrul de 9-12 m), pentru un semnal mai curat. Programele TV transmise prin satelit sunt receptionate de o serie de statii de sol si distribuite prin emitatoare si translatoare pentru acoperirea unui anumit teritoriu sau sunt receptionate direct de catre telespectatori folosind antene individuale. Statiile de sol folosesc emitatoare cu putere de cca 5-10 kW, antene parabolice de cca 20-25 m si sunt dotate cu aparatura necesara de urmarire a evolutiei satelitilor.
De obicei uplink-ul si downlink-ul sunt facute in benzi de frecventa diferite (C sau Ku), pentru evitarea interferentelor.
Satelitii care au banda C folosesc au in jur de 24 de canale de receptare-emitere cu o latime de banda de 36-50 Mbit/s, air cei care au banda KU au pana la 32 de canale receptie-emitere. Pentru evitarea interferentei, satelitii geostationari trebuie sa aiba o distanta intre ei de 2 grade sau de 1 grad, pentru cei cu banda C, respectiv banda Ku. Asta inseamna ca exista un numar limita de sateliti geostationari pentru fiecare banda, obtinut prin impartirea celor 360° ale Pamantului la 2, respectiv la 1.
Satelitii destinati in special televiziunii sunt impartiti in doua categorii:

• sateliti DBS (Direct Broadcast Satellite). Acestia sunt utilizati in servicii de tip DTH (Direct To Home), adica transmisiunea se face direct catre echipamentul folosit de utilizator. Receptia canalelor TV prin satelit in locuinte folosind antena parabolica se face prin acest serviciu. Satelitii folosesc antene parabolice mici, cu diametre de 40-60 cm si polarizare circulara, iar frecventele sunt cele din partea superioara a benzii Ku. Cateva companii furnizoare de servicii DTH sunt: Sky Digital (Marea Britanie), Premiere (Germania), DirecTV (SUA).
• sateliti FSS (Fixed Service Satellite). Acestia opereaza in banda C si portiunile joase ale benzii Ku si folosesc antene parabolice mai mari, cu polarizare lineara, dar cu putere mai mica. Satelitii FSS acopera aproape toate tipurile de servicii de telecomunicatii: transmisiuni catre statii de radio sau televiziune, transmisiuni telefonice sau de date, transmisiuni video in direct, gazduiri de videoconferinte sau invatamant la distanta, transmisiuni catre furnizorii de televiziune prin cablu. Prin serviciul TVRO (Television Receive Only), satelitii FSS reusesc sa furnizeze servicii DTH mai ieftine decat cele ale satelitilor DBS.

Inca un concept des folosit este cel de canal free-to-air, adica acel canal de televiziune care nu are nici un cost de receptare. In Romania de exemplu, astfel de canale free-to-air sunt: Antena 3, Pro TV, Prima TV, TVR international, Realitatea TV, B1TV(fta/conax) etc.
Constelatii de sateliti de televiziune mai importante poarta urmatoarele nume: Intelsat, Americom, Sirius, HotBird, Astra, Arabsat, Spaceway, PanAmSat, Amos.

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CE SUNT SATELITII ?

Satelit este orice obiect care parcurge o traiectorie circulara (care poarta numele de orbita) in jurul altui obiect.
Satelitii Pamantului pot fi naturali (Luna) sau artificiali (construiti de om, apoi lansati pe orbita).
Exista mai multe tipuri de sateliti artificiali, in functie de obiectivele pe care le au de atins:

• sateliti astronomici - folositi pentru cercetare astronomica;
• sateliti de telecomunicatii - folositi pentru a facilita comunicatiile la distanta;
• sateliti de recunoastere - folositi mai mult in scopuri militare si de spionaj;
• sateliti de observare a Pamantului - folositi pentru studii geografice;
• sateliti meteorologici - folositi pentru masurari si prognoza meteorologica;
• statii spatiale - compuse din mai multe module; transportul materialelor si echipajelor catre si de la statia spatiala este efectuat de alte nave spatiale.

De asemenea, exista mai multe tipuri de orbite, dupa care se clasifica si satelitii artificiali:

• Satelitii subsincroni (aflati pe o orbita joasa, la o distanta mai mica de 35786 km de la nivelul marii). Perioada de rotatie a a acestora in jurul Pamantului este mai mica decat perioada de rotatie a Pamantului.
• Satelitii sincroni (aflati pe orbita GEO, la distanta de 35786 km de la nivelul marii).
• Satelitii geostationari (aflati pe orbita GSO) sunt sateliti sincroni a caror orbita se afla in planul ecuatorial al Pamantului si a caror miscare are acelasi sens cu sensul de rotatie a Pamantului. Satelitii geostationari au, practic, o pozitie fixa in raport cu un punct de pe suprafata pamantului (de ex. in raport cu statia de sol).
• Satelitii aflati pe orbite eliptice. Aceste orbite au aparut din cauza dezavantajelor pe care le aveau zonele Pamantului aflate la latitudini mai mari de 60° in cazul in care comunicau cu un satelit geostationar. Cea mai folosita orbita eliptica este Molniya, aflata deasupra Rusiei.