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Satellite Television Glossary

Editors Note: Reprinted with permission of Reed Publications. This glossary is part of the 86┬╗page Satellite Television Handbook available for $7.95 {add $2.00 for 1st class) from Global TVt PO Bom 219-H, Mattland FL 32751. Part II of the glossary will appear in the next issue of 73


Active Device. An electronics component made using transistors to amplify or control a signal See Passive Device (next issue).

Adjacent Channel Interference. Signal distortion because other signals in nearby frequencies are not properly filtered. A bandpass fiiter allows only the selected frequency band to pass through it removing adjacent channels,

AFC (Automatic Frequency Control). A satellite TV receiver feedback circuit which prevents the tuning oscillators from drifting away from the center frequency of the selected channel due to temperature change or other instabilities.. A phase-locked loop demodulator usually provides an AFC output back to the LO.

ACC (Automatic Cain Control). A satellite TV receiver feedback circuit which controls the gain (amplification) of the i-f amplifiers so that the signal input to the demodulator will be constant, despite incoming signals of varying strength from different satellite transponders ACC can be overridden by a manual gain control to make signal strength measurements in most receivers.

Alignment. The process of tuning (or tweaking) a circuit to compensate for the approximate tolerances of the components during assembly, using test equipment.

AM (Amplitude Modulation). An easy method of transmitting program signals on a carrier frequency where the relative strength (amplitude) of the carrier is made proportionally equal to the amplitude of the program signal AM is simpler but more susceptible to noise than FM, Satellite TV uses FM for both audio and video modulation, but the user's TV set takes the satellite TV receiver's output and detects the video as AM, the audio as FM,

ANIK 1. A Canadian TV satellite operated by TELSAT. It has 12 transponders in the vertical format only and is located at 104 degrees west longitude on the geostationary orbit belt

ANIK B. A Canadian TV satellite in the ANIK series located at 109 degrees west longitude. It has 12 vertical transponders.

Aperture Efficiency. The ratio of captured signal to the theoretical maximum for a given dish antenna/feed combination. The design goal is 100% aperture efficiency, but most TVRO dishes perform at only 50-60% to attain low noise characteristics and ease of construction. Some VHF/UHF antennas, on the other hand, can approach the 100% goal with an array of reflective elements.

ARO (Audio Receive Only). Small dish antennas used by radio networks for music and news programming distribution from TV satellites (mostly WESTARS), Dishes 2 meters and smaller have been considered by radio broadcast stations.

Artwork. A printed circuit design term which describes the printed circuit pattern of etched and conductor surfaces on a PC board.

Attenuator. A passive device which causes a known insertion loss in the signal transmission tine, it is commonly used to prevent a very strong signal from overloading a receiver. They are also used as test equipment and in VHF/UHF broadcast reception to eliminate weak ghost signals.

Audio Subcarriers. The sound in a TV satellite composite signal is encoded in a narrow portion ot the video carrier, usually a high-tidefity FM signal at 6.2 or 6.8 MHz as measured after the main signal has been demodulated. Other satellite subcarriers can carry digital and text information as well. Azimuth. Compass direction from due north measured in degrees clockwise, True north can be found by sighting the star Polaris at night, or by applying a iocal correction for magnetic deviation to a compass reading,

Azimuth-Elevation Mount. An inexpensive movable dish antenna mount and aiming system It works like an oarlock where one pivot allows rotation in the horizontal plane about the azimuth angle from due north. The other pivot is the elevation above the horizon. This mount can be more difficult to aim than a polar mount. See Polar Mount (next issue). Balun. An impedance-matching passive device located between a 75~Ohm coaxial cable and a 300-0hm device, such as a TV set or VHF/UHF antenna. Bandpass Filter. A type of electronic frequency filter which severely limits signal frequencies above and below the selected frequencies, preventing adjacent channel interference, Satelfite TV receivers use these also to remove noise from around the edges of the selected channel, usually 30 MHz wide

Baseband. This is the output signal of a video camera, videotape recorder, or satellite TV receiver before remodulation (so that it can be viewed on an ordinary TV set). A signal in a satellite TV receiver goes from 4 CHz through the downconverter to become i-f and then through an FM demodulator to become baseband. American NTSC TV bandwidth is 4.2 MHz at baseband.

Beamwidth. The beamwidth of a dish antenna is the angle of sky which can be illuminated (picked up or sent out) by the dish. Within that arc satellites can be seen from the TVRG dish. Large dishes have narrow beamwidths which reduce noise from its sides. Small dishes have wider beamwidths and are noisier, but easier to aim.

Bias. That part of an amplifier circuit which provides power for a transistor and supplies the energy for its output signal On an LNA, the bias circuits are on a separate PC board.

Bipolar. A type of silicon transistor used in LNAs and other high-frequency, low-noise devices. They are superior in noise quality to ordinary transistors but are inferior to FETs, especially GaAsFETs. Black Bo*. An engineering abstraction in which a de\ ice is considered only for its effect, not for its construction. Naive users can treat satellite TV components as black boxes until they are ready to learn more about them They need to know only what they require and how to hook it together. Blanking Pulses. That part of a video TV signal which for an instant blanks out the screen, enabling the electron beam to fly back to the start of a horizontal line or vertical frame This is wasted time as far as information transmission is concerned and some methods (or multiplexing data channels into a TV picture use the vertical blanking interval. BNC Connector. Easy to lock coaxial cable fittings which interface signals in the i-f portions of a satellite TV receiver They work well in the 70-MHz range. Breadboard Circuit. A prototype of an electronic cir cuit in which changes are easily made, facilitating construction and debugging of the design. Broadcast Satellite. A form of international frequency allocation where only the uplink stations are identified (licensed). See Fixed 5ate///ie for comparison. C Band. A loose military designation for 3,7-4 2-GHz microwave frequency band used for the downlinks of satellite TV signals. Wavelengths are between 8.10 and 7.14 centimeters (319 and 2,81 inches). C/N (Carrier to Noise) Ratio. The ratio of the carrier strength and noise strength measured in dB. The higher the C/N, the higher the S/N and quality of the resulting TV picture. Above 11 dB is superior, above 7 dB is good, and below that the picture quickly becomes extremely noisy. See also S/N (next issue) and FM Improvement (below).

Cable TV. See CATV below.

Carrier. A strong signal occupying a communications channel which is modulated (AM, FM, etc.) to transmit program information. In an abstract sense, the carrier transports the program material from the transmitter to the receiver,

Cassegram Antenna, A folded beam antenna which enjoys the advantages of a long focal length (high aperture efficiency and gain) without the disadvantages of lengthy and awkward feed supports. The subreflector is hyperbolic in cross section and is precisely adjusted to concentrate the incoming microwave fronts to a feedhorn located at the center of the dish If the subreflector is elliptical in cross section, the antenna is also called Gregorian,

CATV (Community Antenna Television). Commonly known as cable TV, it has a central antenna tower (VHF/UHF/FM) together with a satellite TV dish antenna and captures high-quality broadcasts for subsequent sale through a signal distribution system, typically using coaxial cables to each home,

CCIR (International Radio Consultative Committee).

A division of the ITU (International Telecommunications Union) which formulates international standards for radio communications, including the pre-emphasis and de-emphasis of satellite TV signals in a receiver.

CITT (International Telegraph and Telephone Consultative Committee), A division of the ITU (International Telecommunications Union) which formulates international standards for telegraph and telephone communications including uplinks and downlinks of satellite TV, See also CCIR.

Channel. A frequency band allocation which defines the limits of the contamed broadcast carrier signal. In the USA, channels are allocated by the FCC. Chip. An integrated circuit or section of a silicon wafer.

Chip Capacitor. A leadless capacitor small enough to be soldered directly on microstrip or stripline microwave PC boards. They must be used instead of ordinary capacitors because the leads would alter the inductive characteristics of the circuit. They are used to build LNAs,

Chroma. That part of the video signal which contains the color information.

Circular Polarization. Right- or lefthand screw sense of microwave signal polarization used by INTELSAT, A hybrid mode feed should be used to avoid the 3-dB

loss with standard linear {vertical and horizontal polarization) feeds

Circulator. See Isolator

Close-Captioned TV. A text service for the hard-of-hearing TV audience which decodes a text subcarrier and displays it at the bottom of the TV frame on the accompanying video picture It does not interfere with the standard audio FM subcarrier CNR (Carrier to Noise Ratio). See C/N, Coaxial Cable. A signal transmission line that is made using a center conductor separated from a shielding cylindrical outer conductor by a dielectric, usually polyethylene, sometimes air, in a low-loss application ,

Commercial TVRO. A strong dish capable of withstanding hurricane force wjnds, an LNA with a lengthy MTBF (Mean Time Between Failures) and good noise figure, a drift-free, low-distortion receiver, and a high-quality modulator, all operating at a 3-dB margin above the receiver's FM threshold I his system supplies programming for sale through MATV or CATV distribution.

Common Carrier. An operator or lessor of satellite IV transponders which in turn leases them to other parties or transmits programming for others without controlling or owning the content, 4-GHz satellite TV is not legally a broadcast service and the FCC does not make the satellite TV common carriers (RCA Americom, Western Union ) abtde by the constraints of broadcasting law.

Comparator, in an FM demodulator using a phaselot ked loop (PLL), this is the electronic component which compares the phase relationship of the input signal with the signal from the tracking local osolla^ tor (LO). The output signal from the comparator is proportional to the phase error between the two input signals and is used to control the LOt Composite TV Signal. This is a combination of video picture, color, audio, and synchronization information.

COMSTAR I, An American satellite which can carry video but is operated by the telephone company, AT&T. Since it is underutilized, eventually it will carry more video. It has 24 transponders, 12 which are vertical linear polarized and 12 which are horizontal linear polarized. It is located at 128 degrees west longitude.

COMSTAR II. An American satellite, second in the COMSTAR series, which has leased 11 transponders to RCA for cable video programming It also has 24 transponders and is located at 95 degrees west longitude.

COMSTAR 111. An American satellite, third in the COMSTAR series, which like its sisters can be expected to carry more video programming in the future. It also has 24 transponders and is located at 87 degrees west longitude.

dB (decibel). A ratio expressed logarithmically which allows easy calculation of losses and gains. Two signals, SI and 52, can be compared using dB according to the following equation: d8 = 10 tog (S1/S2). Often S2 is a known reference level If a signal is 3 dB over the reference, then it is twice as strong; if it is - 3 dB under the reference, then it is half as strong, dBL Decibel gain of an antenna over a reference antenna, dBm, Decibel power of a signal over a 1-milliwatt reference dBW. Decibel power of a signal over a l-Watt reference

De-emphasis. A selective restoration of the high-frequency end of a satellite TV channel within the satellite TV receiver. This is performed after the FM carrier is demodulated to baseband. See also Pre-emphasis (next issueJL

Detector. A demodulator circuit in a receiver which extracts the program signal from the carrier

Dielectric. An electrical insulator which can carry an electric field when near a conductor. It is used to make transmission lines, microwave PC boards, and capacitors.

Diplexer, A section of waveguide which joins two microwave signals in an uplink Earth station. Dipole, An active antenna element located in the feed which collects the concentrated satellite I V signal and conducts it to the LNAr It is called a probe in this case.

Directional Coupler. In an MATV or CATV signal distribution system, this passive device drops a signal line for a subscriber's TV set from the main trunk line. !t is a superior performance signal splitter from the high level (strength) trunk line.

Discrete Components. Unlike an integrated circuit (IC), in this assembly technique each part is built separately and then assembled. Discriminator. An FM demodulator circuit in a satellite TV receiver.

Dithering, See Energy Dispersal Waveform* DOMSAT (Domestic Satellite), Distinguishes US and Canadian satellites from INTELSATs. Double Conversion, This downconversion technique converts from 4 GHz to the final i-f (typically 70 MHz) in two stages instead of just one, so that potential image noise from the first mixer stage is eliminated See also Single Conversion (next issueI

Downconversion. The process of converting the 3.7-4.2-CHz microwave signal down into a frequency range in which signal processing components are less expensive Typically, this is a VHF frequency of 70 MHz.

Downconverter. A microwave part (consisting of local oscillators (LO). mixers, and bandpass filters) which accomplishes downconversion This is the front end of a satellite TV receiver Downlink. The communication path from a TV satellite to its ground (Earth) stations. Duroid. I he brand name of a microwave printed circuit board specified in many LNA and downconvert-er plans, Mostly D-5880 226-127 from Rogers Corp. has been used.

Dynamic Range. The weakest through strongest signals that a receiver will accept as input. Signals which are too weak cause excess noise and signals which are too strong cause overloading and possibly modulation distortion

East Coast Feed, Satellite TV programming scheduled for the convenience of US east coast viewers (Eastern Time Zone)

EIRP (Effective Isotropic Radiated Power). A measure of the relative strength of the satellite TV signal ex-

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