Terms
- Analog:
- Used to transmit audio, such as voice, radio, stereo, and control
tones.
- Antenna:
- The device used to radiate or receive signals through the air, sometimes
called a “dish”.
- Availability:
- The amount of time (generally expressed as a percentage) that a satellite
signal is above threshold at a given downlink locations, on average.
Also expressed as 99.9% (“three nine” availability) or as
99.99% (“four nine” availability). Downtime is due to rain
outage per site per year on average over 5 years. (99.9% = 8 hours and
53 minutes outage per year.)
- Backhaul:
- Means by which audio or data is transmitted to an uplink facility,
i.e. SCPC, dedicated leased line (phone line) or video carrier.
- Band:
- A unit for designating a specific frequency or range of frequencies
in the electromagnetic spectrum. Satellite communications most commonly
use the C-Band (6/4 GHz) or Ku-Band (14/11 and 14/12 GHz) frequencies.
Future satellite systems will make use of bands above 20 GHz to gain
additional capacity and to avoid congestion and interference with systems
operating at lower frequencies.
- Bandwidth:
- A means of capacity that indicates the amount of frequency spectrum
required by a telecommunications service or system. (The range of frequencies
available for signaling.) Services requiring bandwidth greater than
200 KHz are known as “broadband.” Those requiring less capacity
are “narrowband”. Also, the numerical difference in Hertz
(Hz) between the highest and lowest in use.
- Baud:
- Unit of signaling speed. The speed in baud is the number of discrete
conditions or events per second.
- Broadband:
- A term used to describe high bandwidth, or bit rate transmission of
data signals.
- C-Band:
- The 3.7 to 4.2 GHz downlink and 5.925 to 6.425 GHz uplink band of
frequencies at which some broadcast satellites operate.
- Caching:
- The use of memory in a file server to store information so the next
time the information is requested it can be served from memory instead
of from the source.
- Channel:
- A one-way communications link.
- Circuit:
- A two-way communications link.
- CIT:
- SpaceCom’s Network Operations Center (NOC). The Chicago International
Teleport®, a $15 million redundant uplink facility owned and operated
by SpaceCom, located in Monee, IL.
- Communications Satellite:
- A space vehicle launched into orbit to relay audio, data or video
signals as part of a telecommunications network. Signals are transmitted
to the satellite from earth station antennas, amplified and sent back
to earth for reception by other earth station antennas. Satellites are
capable of linking two points, one point with many others, or multiple
locations with other multiple locations. Commonly called a “bird”.
- Decibel (dB):
- A measurement of transmission loss or gain in the form of a ratio
between two voltages, currents, or powers. 3dB=double the power, 10dB=10
times the power. Decibels relative to one watt or milliwatt are abbreviated
as dBw and dBm, respectively. FM Cubed® is 44.3 to 48.3 dBw EIRP.
Ku-Band FM Squared® is 41.3 to 45.3 dBw EIRP while SCPC systems
are typically 14 to 21 dBw and are normally restricted by the FCC to
be 6 dB per 4 KHz.
- Digital:
- A means for encoding information in a communications signal through
the use of bits (binary digits). Digital transmission is increasingly
replacing analog transmission because it provides more efficiency and
flexibility for networking.
- Downlink Antenna:
- The part of the satellite communication system by which information
is received from the satellite. Also the earth station receive antenna.
- DVB (digital video broadcasting):
- An MPEG-2 compliant technology for digital audio and video or high
bandwidth applications. SpaceCom has launched a C-Band DVB satellite
technology called FM Quad®. SpaceCom’s DVB has half rate forward
error correction (FEC) and QPSK (quadrature phase shift key) modulation.
- Encryption:
- The technique of modifying a known bit stream on a transmission line
such that it appears to be a random sequence of bits to an unauthorized
observer.
- Ethernet:
- A proprietary contention bus network developed by Xerox, Digital Equipment
Corporation and Intel. It formed the basis for the IEEE 802.3 standard.
- Extranet:
- A virtual network tying a company to outside organizations, often
through the Internet, but also through frame-relay and other such network
services.
- Fiber Optics:
- Transmission lines made of thin glass fibers optimized to carry light
waves. It is possible to carry information on light waves in the same
way it is possible to carry information on radio waves.
- Focal Length:
- The distance from the center of the reflector to the feed opening.
- Footprint:
- The portion of the earth’s surface covered by the signal from
a communications satellite; the area within which a satellite's signal
can be received.
- FM
Cubed®:
- A Ku-Band time division multiplexing satellite technology using frequency
modulation invented by SpaceCom for digital applications. FM Cubed®
has one of the strongest signal strengths and extremely high availability
for commercial satellite applications.
- FM
Squared®:
- A Ku-Band or C-Band frequency division multiplexing satellite technology
using frequency modulation invented by SpaceCom for analog, audio and
digital applications.
- FM
Quad®:
- A SpaceCom provided C-Band packet division multiplexing satellite
technology using QPSK (quadrature phase shift key) modulation. It is
DVB MPEG-2 compliant (see also DVB).
- Footprint Map:
- A satellite coverage map that expresses the area of a satellite beam
via a series of contours which delineate decreasing value of antenna
sizes, power flux-density (PFD) levels, EIRP, or G/T.
- Frequency:
- The number of cycles per second of an electromagnetic signal expressed
in Hertz (Hz).
- Frequency Division Multiplexing (FDM):
- The division of a given bandwidth into various subdivisions, with
each having enough bandwidth to carry one voice or data connection,
such as FM Squared®.
- Frequency Modulation (FM):
- The process of changing a “carrier” wave so that the frequency
of the “carrier” wave varies relative to the information to
be transmitted.
- Gateway:
- A network device that selects routes to a source or destination of
information, such as a computer, printer, server, router or other addressable
unit, based on an address which is unique to each device.
- GigaHertz (GHz):
- A unit of frequency equal to one billion cycles per second.
- Hertz (Hz):
- A unit of frequency equal to one cycle per second. Named after the
19th century German physicist Heinrich Hertz.
- International Telecommunications Satellite Organization:
- An organization formed by 91 countries for managing global communications
satellite systems (commonly known as Intelsat).
- Intranet:
- A network linking a company’s offices and making information
accessible, usually with a web browser.
- IP:
- Internet Protocol. A connectionless protocol used for delivering data
packets from host to host across an internetwork i.e. the Internet.
- Kbps:
- Kilo (one thousand) bits per second (speed)
- KiloHertz (KHz):
- One thousand cycles per second.
- Ku-Band:
- The microwave frequency band between 11.7 and 12.2 GHz receive, 14.0
to 14.5 GHz transmit. It is more susceptible to rainfade (compared to
C-Band); however, it allows substantially smaller antennas and it is
much more immune to terrestrial interference and noise.
- Low Noise Block Down Converter (LNB):
- Also called low noise amplifier (LNA). Down converts the whole 500
MHz satellite bandwidth to one intermediate, usually L-Band, frequency
range.
- L-Band:
- The frequency band between 950 to 1450 KHz.
- Mbps:
- Mega (one million) bits per second (speed)
- MegaHertz (MHz):
- A unit of frequency equal to one million cycles per second.
- Microwave:
- The frequency range from approximately 500 MegaHertz (MHz) to 30 GigaHertz
(GHz).
- Modulation:
- The method by which data or audio is imprinted onto a carrier. FM
Squared® and FM Cubed® use Frequency Shift Key (FSK) modulation.
Other methods of modulation are Quadrature Phase Shift Key (QPSK), Binary
Phase Shift Key (BPSK) and Minimum Shift Key (MSK).
- MPEG-2:
- A public standard for video compression intended for broadcast video.
It compresses a high-definition television signal (25 MHz) into the
channel allocated to broadcast television (6-MHz). (MPEG= Motion Pictures
Experts Group which developed the standard)
- Multiplexing:
- Combining two or more message channels for simultaneous transmission
over a common path; analog systems use frequency-division multiplexing,
while digital systems employ time-division multiplexing.
- Noise:
- An unwanted signal which interferes with reception of the desired
information. Noise is often expressed in degrees Kelvin or decibels.
- Parity Bit:
- A bit that is set at “0” or “1” in a character
to ensure that the total number of 1 bits in the data field is even
or odd. Used for error detection.
- Polarization:
- A characteristic of the electromagnetic wave. Four senses of polarization
are used in satellite transmissions: horizontal; vertical, right-hand
circular; and left-hand circular. LNB’s have a polarization setting
to match the transponder orientation.
- Real Time:
- A telecommunications or data processing system that responds immediately,
in the same time frame as the user provides input.
- Redundancy:
- Capacity to ensure continuity of service through backup equipment
when there is a malfunction in primary service Satellite Antenna or
earth station: The communication system (dish, receivers, transmitters
and other equipment) used to send or receive electronic signals from
or to a satellite. VSAT: Very small aperture dish-shaped antenna device
– usually only 3 to 6 feet in diameter.
- Satellite Receiver:
- The indoors electronic component of an earth station which down converts,
processes (by demultiplexing and demodulating) and prepares satellite
signals for viewing or listening.
- Single Channel Per Carrier (SCPC):
- A satellite system that employs a separate carrier for each channel,
as opposed to frequency division multiplexing (FM Squared®, sometimes
called FM/FM) that combines many channels on a single carrier.
- Space Segment:
- Term which usually identifies the bandwidth and power for a satellite
communications channel.
- Streaming video/audio:
- The result of a video/audio signal which has been digitized and compressed
for Internet viewing. The higher the compression rates, the lower the
video/audio quality. Typical streaming connections vary from a low of
20 kbps for audio only to 300+ kbps for audio and video.
- Subcarriers:
- An auxiliary carrier linked to the main carrier in a communications
systems, which can carry audio or data information. Subcarriers are
frequently broadcast on the unused portion of video (TV) transponders.
Like SCPC, they may be used for backhaul or primary distribution.
- TCP/IP or Transmission Control Protocol:
- A connection oriented protocol designed for operation on the Internet.
Considered to be a common language between otherwise incompatible computers.
- Teleport:
- The name commonly given to the satellite communications uplink facility.
- Time Division Multiplexing (TDM):
- The division of a digital transmission channel into multiple slower
speed channels by allocating a particular time slot to the slower speed
channels. FM Cubed® is a TDM system and is similar to a T-1 phone
line. (e.g. customer #1 gets bit 1, 65, and 129, etc. and customer #2
gets bit 2, 66, and 130, etc.)
- Transponder:
- The portion of a communications satellite that receives audio, data
and video signals from earth, alters their frequency, amplifies the
signals and retransmits them to earth. Satellites carry numerous transponders
on board.
- Two-way:
- Bi-directional, upstream and downstream transmission capability.
- Uplink:
- The earth station electronics and antenna that transmits information
to the communication satellite.
- VSAT:
- Very Small Aperture Terminal. Frequently used as another name for
two-way satellite technology.
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