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Satellite Radio Glossary

Satellite Radio Glossary

Here are a list of terms you will run across while reading about and using Satellite Radio.


Term Description
Air Shift The hours that a DJ or PJ works on the air at a given time. The average air shift is 4 hours - 6 - 10 A.M., 10 A.M. - 2 P.M., etc.; however, air shifts can typical be up to 6 hours, especially for a deejay who does an early evening or overnight shift.
Aircheck An aircheck is a recorded copy of a broadcast, either digitally or on magnetic tape.
Analog The principal feature of an analog signal is that they are continuous in nature rather than pulsed or discrete nature
Antenna A piece of equipment that allows transmission and reception of radio signals. Satellites need antennas to communicate with earth.
Antenna Alignment / Antenna Pointing The process of optimizing the orientation of a satellite antenna's main direction of sensitivity towards the satellite to maximize the received signal level and to minimize the chance of receiving unwanted interference from other satellite systems.
Antenna Noise Temperature A receiving antenna collects noise from radiating bodies falling within its radiation pattern. For an on-ground receiving antenna, this includes contributions from the sky and from the earth. The combined affect of these noise sources is modeled by an equivalent noise temperature for the antenna, which varies with elevation angle and antenna size.
Arbitron An international media and marketing firm that provides the industry-accepted standard of audience measurement for radio. "Arbitron" can also refer to the actual survey, published four times-a-year.
Beacon A stationary transmitter that emits signals in all directions (also called a non-directional beacon). It is used by earth stations equipped with an automatic satellite tracking system. Beacons can be generated on-board the satellite or transmitted from the ground and relayed through the satellite.
Beamwidth A measure of the ability of an antenna to focus signal energy towards a particular direction in space, either towards the satellite for a ground-based transmitting antenna or to collect signal energy from a particular direction in space - from the satellite for a ground-based receiving antenna.
Boresight The alignment of a directional antenna, using either an optical procedure or a fixed target at a known location. The direction of maximum antenna gain. For a receiving antenna, the boresight is aligned with the satellite as accurately as possible for maximum received signal strength.
Circular Orbit A satellite orbit where the distance between the centers of mass of the satellite and of the earth is constant.
Clarke Belt The circular orbit at approximately 35,800 km above the equator, where the satellites travel at the same speed as the earth's rotation (Geostationary Orbit) and thus appear to be stationary to an observer on earth. Named after Arthur C. Clarke, physicist and science fiction writer in the USA who mathematically calculated the geostationary earth bit.
Clear Sky Describes the weather conditions encountered at the terrestrial end of an earth-to-space path of a satellite communication link. It describes the condition where the decrease of radio waves caused by precipitation (rain, snow, sleet, dew, etc.) is lowest (i.e. cloud-free sky and good visibility).
Cross Modulation Signal distortion or interference caused by the modulation of one carrier affecting another signal. It is usually due to nonlinear device operation, which can be caused by overloading an amplifier and is worsened by signal power level imbalances.
Data Compression
(Data Reduction)
Data compression (or data reduction) reduces the information in a digital music file by removing non-essential data, reducing the size of the file by as much as fifteen to one. This process makes it possible for satellite radio providers to store, transfer and broadcast huge quantities of musical information.
Docking Station A cradle with an adjustable stand that can be installed in your care or home. The tuner can be transported easily from one permanently mounted docking station to another one, so it's easily moveable from car to home and back.
Downlink The microwave connection between the satellite and the receiving station on the ground.
Earth Space Link Any communications link between an earth station and a satellite (uplink or downlink).
Earth Station An installation of an antenna and associated equipment which is located on the earth's surface and intended for communication with one or more satellites. The term is usually understood to refer to the ensemble of equipment that is needed to effect communications via satellite.
Earth Station The term used to describe the equipment (antenna, low-noise amplifier (LNA), down-converter, and receiver electronics) used to receive a signal transmitted by a satellite.
External Satellite Radio Tuner The outboard "black box" that receives the satellite radio signal controlled by a same-brand receiver with satellite radio controls. It also requires a specialized antenna and service subscription in order to receive the satellite radio signal.
Fixed-satellite service (FSS) A radio communication service between earth stations at given fixed positions via one or more satellites.
Footprint The ground area with which a satellite transponder in geostationary orbit can communicate. A footprint can be as large as an entire country. For example, many Canadian satellites have footprints almost the entire size of Canada. There is usually a different map for each transponder (or group of transponders) as each may be aimed to cover different areas of the ground.
Geostationary A circular orbit above the earth, in the plane of the earth's equator, at such speed revolving around the earth that it appears to remain stationary with respect to the earth's surface. See also Clarke Belt.
Geostationary Orbit The circular orbit of a geosynchronous satellite whose orbit lies in the plane of the earth's equator. A perfectly stable geostationary orbit is an ideal that can only be approximated. In reality the satellite will drift out of this orbit because of disturbances such as the solar wind, radiation pressure, variations in the Earth's gravitational field and the gravitational effect of the moon and sun. Thrusters must be used to maintain the orbit in a process known as stationkeeping.
Geostationary Satellite A satellite that appears to be located at a fixed point in space when viewed from the earth's surface. It would appear to hover at the same point in the sky as opposed to how the sun, moon and stars traverse the heavens behind it.
Geosynchronous Orbiting the earth at the earth's rotational speed and with the same direction of rotation. The object will appear at the same position in the sky at a particular time each day, but will not appear stationary if not orbiting in the equatorial plane. If such a satellite's orbit lies over the equator, it is called a geostationary satellite.
Global Positioning Signal (GPS) Satellite technology that uses mathematics to calculate the position in three dimensions (latitude, longitude, and altitude) of something on the earth by measuring the time it takes for the satellite's radio transmissions, traveling at the speed of light, to reach the a receiver on the ground. It requires a fleet of satellites in space and is used for determining a position on the Earth, measuring the Earth's movement after an earthquake or locating drop points for airlifted relief supplies.
Ground Segment Consists of all the earth stations that are operating within a particular satellite system or network. They can be connected to the end-user's equipment directly or via a terrestrial network.
Ground Station An alternative phrase for an Earth Station.
Inclination The angle between the plane of the orbit of a satellite and the equatorial plane. An orbit of a perfectly-geostationary satellite has an inclination of zero.
Inclined Orbit An orbit that approximates the geostationary orbit but whose plane is tilted slightly with respect to the equatorial plane, with the consequence that the satellite appears to move about its nominal position in a daily "figure-of-eight" motion when viewed from the ground. Satellites are often allowed to drift into an inclined orbit near the end of their nominal lifetime in order to conserve fuel on-board the satellite, which would otherwise be used to correct this natural drift caused by the gravitational pull of the sun and the moon.
Individual Reception The direct reception of satellite signals by simple home installations, in particular those equipped with a small antenna.
Micro-coaxial Cable The ultra-thin cable used for satellite radio antennas - it is ideal for routing under rear window molding.
Multibeam Generally refers to the use of multiple antenna beams on board the satellite to cover a contiguous geographical area, instead of a single wide-area beam. Multibeam architectures are often considered for satellites operating in the Ka-band, which is characterized by narrower beamwidths with respect to the Ku-band. Single, wide-area beams predominate in the latter.
Noise Any unwanted electrical disturbance in a circuit or communication channel. When combined with a received signal, it affects the receiver's ability to correctly reproduce the original signal. Also known as Thermal Noise. It is always present to some extent.
Off-Axis Any direction in space that does not correspond to an antenna's boresight direction.
Playlist The official list of songs a station is playing during any given week. In some formats, these lists are looked on as very important since they are submitted to trade newspapers and magazines and compiled to reflect national airplay and trends. In some other formats, like oldies, a playlist does not carry as much weight since it is not a reflection of current songs being played.
Plug-and-Play Satellite Radio A plug-and-play satellite radio tuner can be transferred from car to home, simply by plugging the tuner into a docking station in either location. A plug-and-play tuner has its own controls and line output, so it can be connected to any receiver with an auxiliary input.
Polar Mount A mechanical support structure for an earth station antenna that permits the satellites in the geosynchronous arc to be scanned with steering of a single axis.
Portable Satellite Radio A portable satellite radio tuner, sometimes referred to as a handheld portable tuner. Works much like a portable CD or MP3 player - it lets you carry the tuner around (by clipping it to your belt, for example) and listen to satellite radio using headphones anywhere you can find a signal. Portable tuners feature rechargeable batteries and built-in satellite radio antennas. Most also come with the accessories that allow them to be used as plug-and-play tuners as well.
Program Associated Data The term refers to the transmission of the artist, song title, program and the name of the channel.
Regenerative A term used to describe satellite systems/transponders that recover the original signals from the modulated signals received from the ground, process them in some way, then use them to modulate carriers for retransmission at the downlink frequencies, possibly with a different format. Regenerative repeaters are complex and are often featured in the designs of future, advanced satellite systems.
Repeater A device that amplifies or augments incoming electrical signals and retransmits them towards the earth station(s) at a different frequency. In the satellite context, the term "repeater" usually refers to all Payload equipment, with the exception of the satellite antennas.
RF Modulator Also called an "FM modulator," a Radio Frequency modulator converts the satellite signal to an FM frequency, so you can listen to satellite radio programming on a conventional FM radio. Many manufacturers offer packages which combine a satellite radio tuner with an RF modulator.
Satellite Something that is in orbit around something else. For example, the moon is a satellite of the earth. An artificial satellite is a satellite that was constructed and placed in orbit by humans.
Satellite Link A radio link between a transmitting earth station and a receiving earth station through a communications satellite. A satellite link comprises one uplink and one downlink.
Satellite Network One or more communications satellites and the cooperating earth stations.
Satellite Payload Storage of all equipment on-board a satellite that is dedicated to the reception, frequency conversion, processing, transmission and retransmission of radio signals, including the satellite antennas, but excluding the support equipment such as the platform (physical structure), power supplies and thermal control equipment.
Satellite Radio Antenna A specialized roof or glass mounted antenna which must be used in order to receive the satellite radio.
Satellite Radio Controls Receivers with satellite radio controls operate same-brand external satellite radio tuners. A specialized antenna and service subscription are also required (in addition to the tuner) in order to receive the satellite radio signal.
Satellite Radio Ready New car ready: Be aware, "ready" means only that your in-dash radio will work with a satellite radio, but the tuner itself and the required antenna, are not yet installed. The car dealership may quote a price of several hundred dollars or more for the equipment and installation. That's the bad news. The good news is that you don't have to go with a dealer-installed tuner and antenna. You can purchase aftermarket gear and install it yourself for great results and big some savings. However, you will be giving up one benefit of the factory option: a very clean installation, with no visible hardware which is easy to steal.
Skyplex A system which multiplexes several digital television and entertainment services on-board the satellite, instead of on the ground, and retransmits them via a single, DVB-compliant carrier. This permits services to be delivered directly from different geographical locations to end-users located within a broadcast beam and equipped with standard DVB-compliant IRDs. The Skyplex system requires advanced on-board processing equipment for signal reception, multiplexing and retransmission.
Solar Outage This occurs when the sun crosses the earth's equatorial plane during the spring and fall equinoxes. The sun aligns directly behind the satellites for a few minutes each day. This field of view is usually wider than the beamwidth. Solar outages can be exactly predicted as to the timing for each site.
Space Segment Commonly used to refer to the satellites of a particular satellite communication system.
Spot Beam An antenna radiation pattern designed to serve a relatively small or isolated geographic area, usually with high gain. The radio frequency equivalent of a spotlight.
Sun Outage Sun-Satellite Conjunction can cause a large increase in the noise received by an earth station that is pointed towards the satellite, which degrades the signal quality and can even cause the signal to be lost for a short time. While this is an unavoidable physical phenomenon, it does not affect the relatively small antennas that are used for individual and collective reception of broadcast television and entertainment services.
ThruGlass Technology A Terk innovation. Antennas with ThruGlass technology are mounted on a window. An interior coupler is hardwired to the satellite radio receiver. The antenna and coupler pass RF signals and DC power to each other through the glass, eliminating the need to run a cable from the antenna to the receiver.
Tracking The process of continuously adjusting the orientation of an antenna so that its boresight follows the movements of the satellite about its nominal position. Used in earth stations equipped with large antennas and earth stations operating to satellites in inclined orbit.
Transponder Every satellite is equipped with a certain number of transponders and every transponder can transmit at least one TV channel (ASTRA) or in some cases two channels (EUTELSAT, Intelsat). The transponder receives a signal from earth and transmits it back to earth at a different frequency.
Uplinked The process by which a station on the ground transmits information and instructions up to a satellite.
XM NavTraffic™ Service When used in conjunction with a GPS satellite navigation receiver, NavTraffic™ provides up-to-the-minute information on road conditions, accidents, lane closures, traffic flow (speed) and delays along the route you've programmed. It will alert you to scheduled traffic incidents, such as traffic diversions because of sporting events, and road construction.


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