GLOSSARY

Physical Units & Definitions | Satellite Terminology | Devices / Hardware | Signal Processing

A	B	C	D	F	H	I	L
M	O	P	Q	R	S	T	U

A / B Switch	A switch in a satellite receive earth station, which has two inputs and a single output. Each switch input is connected to the output of an LNB. The single switch output is usually connected to a satellite receiver (set-top box). The switch permits selection of one of the two LNB inputs (A or B) for routing it to the common output (to a receiver for example), whilst providing adequate isolation between the signals produced by each LNB.
Aerial	See Antenna.
Amplifier	An electronic device used to increase the strength (power) of a signal fed into it.
Antenna	A device for transmitting or receiving radio waves. Also known as aerial. In satellite communication systems the antenna usually consists of a parabolic reflector and a feedhorn. In a receiving system the reflector focuses radio waves onto the feedhorn for detection and conversion into electrical signals. In a transmitting systems the reflector concentrates the radio waves emitted by the feedhorn into a narrow beam aimed towards the satellite.
Antenna Efficiency	The ratio of the signal strength transmitted towards or received from a particular direction in space by a real antenna to the signal strength that would be obtained with a theoretically perfect antenna of the same physical size. This ratio is usually expressed as a percentage.
Antenna Illumination	The radiation of electromagnetic energy from the feedhorn to the surface of the parabolic reflector of a transmit antenna, or the focusing of electromagnetic energy captured by the reflector of a receiving antenna towards the feedhorn. With perfect illumination no signal energy is lost to the surrounding terrain. In practice there is always some loss.
Antenna Aperture	The total reflective area of a parabolic antenna (dish) over which radio waves are captured or radiated. The effective aperture is smaller than the physical aperture and is related to it by the Antenna Efficiency.
Aspect Ratio (Television)	The ratio of the width of a television picture or television screen to its height . The ratio for conventional television systems is 4:3. In advanced television systems (e.g. widescreen) the ratio is usually 14:9 or 16:9, which better approximate the aspect ratio used in cinema.
Attenuator	A passive device that weakens a signal that passes through it. The amount by which the signal power is reduced is usually expressed in decibels.
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Bandpass Filter	A circuit or device that allows only a specified range of frequencies to pass from input to output, rejecting all signals at lower or higher frequencies.
BNC Connector	A twist-lock coaxial connector that is commonly used on commercial video equipment and on some brands of satellite receiver.
BUC	Block Up-Converter: Earth station transmitter combining signal up-conversion and power amplification in a single unit, normally located directly at the antenna input, or close to it.
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Coaxial (Screened) Cable	A cable consisting of an inner insulated core of stranded or solid wire surrounded by an outer insulated flexible wire braid. Used principally as a transmission line for radio frequency signals with low loss. Commonly shortened to Coax. Sometimes referred to as screened cable because the outer braid screens the inner conductor from electrical interference.
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Decoder	A circuit or device that restores a coded signal to its original form based on knowledge of the process used to code the signal.
Demodulator	A device that recovers the original signal from a modulated carrier signal, such that the characteristics of the original are faithfully reproduced. Implements the process of Demodulation.
Descrambler	A device that recovers the original signal from one that has been rendered unintelligible by Scrambling.
DiSEqC™	Digital Satellite Equipment Control. A standardised method for two-way communication between devices in satellite reception systems. Information is exchanged between devices interconnected by standard coaxial cable by means of a modulated 22 kHz tone. DiSEqC™ is a trademark of Eutelsat.
Digital-to-Analogue Converter	A device that converts a digital signal (a series of numbers or other characters) into its equivalent analogue form (a continuously-varying signal voltage).
Diplexer	A device that splits a collection of signals into two groups according to the frequency range in which they are located, or combines two groups of signals, each occupying a separate frequency range, into a single collection of signals.
Dish	Parabolic microwave antenna used for transmitting and/or receiving satellite signals. The term is derived from the shape of the reflector surface, but is taken to mean the whole of the antenna subsystem, including the feedhorn and the antenna structure.
Downconverter	A device for converting the frequency of a signal to a lower frequency. See also Downconversion and Frequency Conversion.
Dual-Band Feed(horn)	A feedhorn that can simultaneously receive signals in two different frequency bands, for instance the C-band (4 GHz) and the Ku-band (11/12 GHz).
Dual Feed	An antenna system consisting of a reflector, a support structure and two LNBs, each equipped with a separate feedhorn or sharing an integrated feed assembly. The focal point of each feed is set so that the antenna system can receive from two different satellite orbital positions simultaneously. The angular separation between satellite positions is usually around 6 degrees, although other angles are possible.
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F-Connector	A standard, low-cost RF connector used to terminate the coaxial cables that interconnect satellite reception equipment (e.g. for connecting the LNB output to the satellite receiver's input).
F / D Ratio	The ratio of an antenna's focal length to its diameter. It describes the basic geometric architecture of the antenna, which affects its physical size, its design and its electrical performance.
Feedhorn (Feed)	A device resembling a horn that emits radio waves in a concentrated beam or collects and focuses radio waves that are incident on its aperture. In a receiving system it collects microwave signals reflected from the surface of the antenna. In a transmitting system it directs microwave signals onto the reflector surface for focussing into a narrow beam aimed at the satellite. The feed is mounted at the focus of the parabolic reflector. It is usually designed to match a particular antenna geometry (F/D ratio).
Filter	A device that blocks signals or radiation of certain frequencies while allowing others to pass unaltered.
Focal Length	The distance from the reflective surface of an antenna to its focal point, usually measured in the horizontal plane. Incoming satellite signals are directed to the Feedhorn which is normally located at the focal point. See also f/D ratio.
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HPA	High Power Amplifier
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Isotropic Antenna	A theoretical device that radiates energy or receives energy equally from all directions.
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Line Amplifier	An amplifier in a (long) transmission line that boosts the strength of a signal to an exploitable level.
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.
LNA	Low Noise Amplifier. A device that receives and amplifies weak satellite signals at the output of a feedhorn, whilst introducing as little electrical noise as possible in the process. The frequency of the incoming signal is unchanged at the output of the device. The feedhorn is typically a physically separate device.
LNB	Low Noise Block Downconverter. A device that processes weak satellite signals directed by an antenna reflector into a feedhorn, whilst introducing as little electrical noise as possible in the process. An LNB consists of a microwave detector followed by a high gain, low noise microwave amplifier and a frequency converter, which downconverts a block of frequencies (group of satellite signals) to a lower intermediate frequency range (typically 950 to 2150 MHz). The feedhorn is often integrated with LNB in a single mechanical unit.
Local Oscillator (LO)	A single-frequency reference signal of high purity which is used by a mixer to convert a communications signal to a higher or lower frequency band.
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Mixer	A device in which two or more input signals are combined to give a single output signal. In satellite communication systems, it is a non-linear device used to generate a replica of an input signal at a higher or lower frequency by multiplying the input signal by a pure tone of a different frequency (the "local oscillator" signal). Usually part of a frequency conversion process. For example, an LNB local oscillator signal at 10.6 GHz mixed with incoming signal at 12 GHz would convert the input signal to an IF frequency of 12 -10.6 = 1.4 GHz.
Modulator	A device which superimposes the amplitude, frequency or phase of a wave or signal onto another wave or signal (a carrier), which is then used to convey the original signal via a transmission medium (e.g. satellite link).
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Offset (Fed) Antenna	An antenna having a feedhorn that is offset from the centre of the reflector. It generally offers better performance than a symmetrically-fed antenna because the feed system does not block the main reflector aperture.
Offset Feed	A LNB that is slightly displaced with respect to the focal point of the reflector so that it receives signals originating from a different direction to that obtained with an LNB placed at the focal point. A technique used in dual-feed reception systems, which receive signals from satellites located at two different orbital locations.
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Preamplifier	A device that amplifies a weak signal for subsequent processing, which may include further signal amplification. In an SMATV system, it is the amplifier mounted adjacent to an antenna to increase the strength of the signal prior to its processing at the headend.
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Quad / Quattro LNB

An LNB providing four outputs simultaneously. It is used to deliver signals received on both linear polarisations (horizontal and vertical) and in both frequency bands (high and low). Each output delivers the signals received on one polarisation and in one frequency band. It is used in collective reception systems to ensure that all services are available to all subscribers, regardless of the service (TV programme) selected by any individual.

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Receiver	The equipment that receives incoming electrical signals or modulated radio waves and converts them into the original audio, video or data signals.
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Satellite Receiver	A receiver designed for satellite reception system, which receives modulated signals from an LNA or LNB and converts them into their original form suitable for direct presentation to the user. See also IRD.
SCART	Also known as Euroconnector or Peritel. Twenty-one-pin connector commonly used in Europe to interconnect satellite receivers, television sets and other audiovisual equipment (e.g. videocassette recorders).
Scrambler	A device that renders a signal unintelligible and/or randomises its content. See also Scrambling.
Splitter	A device that takes an input signal and splits it into two or more identical output signals, each a replica of the input signal but with a different amplitude (typically).
SSPA	Solid State Power Amplifier. A high power amplifier using solid state technology (i.e. transistors). Used for low and medium power applications.
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TWTA	Travelling Wave Tube Amplifier. A high power amplifier based on tube technology. Normally employed when high output power levels are required.
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Universal LNB	An LNB that is capable of receiving a signal transmitted on any linear polarisation and at any frequency within the range 10.7 - 12.75 GHz, usually by means of band and polarisation switching.
Unwanted Emissions	Any undesired emission resulting from the radiocommunication process, which could potentially interfere with other systems. Formal definition: the combination of spurious emissions and out-of-band emissions.
Upconverter	A device for converting the frequency of a signal into a higher frequency. See also Upconversion and Frequency Conversion.
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