Functional Block Diagram - Blonder Tongue Laboratories Inc.

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Broadband Specification Guide CATV Terms & Definitions 8VSB 8VSB is the 8-level vestigial sideband modulation method adopted for terrestrial broadcast by the ATSC digital television standard in the United States, Canada, and other countries. The 6 MHz channel used for ATSC broadcasts carries 19.39 Mbit/s of usable data. Absorption In an optical fiber, loss of optical power resulting from conversion of that power into heat. Absorption Losses Losses caused by impurities, principally transition metals and neighboring elements (Cr, Mn, Fe, Co, Ni), and also by water as well as intrinsic material absorption. AC Hum Modulation (See Hum Modulation) Acceptance Angle Half the vertex angle of that cone within which optical power may be coupled into bound modes of an optical waveguide. Acceptance Cone A cone whose included angle is equal to twice the acceptance angle. Active Containing, or connected to and using, a source of energy. Aerial Cable Cable suspended in the air on poles or other overhead structures. Usually implies the use of a "messenger strand" to which the cable is lashed for support. Alternating Current (AC) An electric current which continually varies in amount, and reverses its direction periodically. The plot of current vs. time is usually a sine wave. AML (Amplitude Modulated Link) A registered trademark for microwave equipment that is manufactured by Hughes Communications Products Co. Ampere Unit of electric current, or rate of flow of electricity. One coulomb per second. One volt impressed across a resistance of one ohm causes a current of one ampere to flow. Amplification The act of increasing the amplitude or strength of a signal. Amplifier A device that accepts a signal at it’s input and presents that same signal, without appreciable distortion, but at higher level amplitude, at its output. CATV amplifiers pass and amplify a relatively wide spectrum. Amplifier Spacing The spacing in transmission loss, expressed in decibels, between cascaded, or serially connected, amplifiers. Also sometimes used to denote the linear cable distance between amplifiers in a system. Amplitude Modulation A process whereby the amplitude of a single frequency carrier is varied in accordance with the instantaneous values of a modulating wave. Analog Signal A signal which is continually variable and not expressed by discrete states of amplitude, frequency, or phase. Angle of <strong>Inc</strong>idence The angle between an incident ray and the normal to a reflecting or refracting surface. Angstrom (A) 10-11 meters. Its use as a unit of optical wavelength has largely been supplanted in recent years by the nanometer (10-9 meter). Anti-reflection Coating A single or multiple layer of thin dielectric coating that reduces the reflectivity of an optical surface. Antenna Gain The ratio, expressed in decibels, of the signal level received or transmitted by an antenna, to the signal level received or transmitted by an isotropic antenna at that same location which is subject to the same power level. APD (See Avalanche Photodiode) Armored Cable A cable having one or two layers of steel tapes or steel wires spirally applied to the sheath to provide mechanical protection. Asynchronous Not synchronous. Attenuation The decrease in signal strength along a conductor, cable, or optical fiber. In an optical fiber acting as a waveguide, it is caused by absorption and scattering. This parameter is usually measured in decibels per kilometer. Attenuation-limited Operation The condition prevailing when the received signal amplitude rather than distortion limits performance. Attenuator A device or network for reducing the amplitude of a signal without introducing distortion. May be fixed or variable, with the loss introduced expressed in decibels. Often called a pad. 80
Broadband Specification Guide CATV Terms & Definitions AGC Abbreviation for Automatic Gain Control. Units with this feature maintain a constant output level when the input signal level varies within a specified AGC range. Agile (Frequency Agile) The capability to change channels quickly and easily, usually by setting switches, i.e. agile modulator, agile processor. Amplifier Device used to increase strength of TV signals. Attenuation Reduction of signal strength. Attenuator Device used to receive radiated electro-magnetic signals such as radio or TV. Atmosphere The gaseous envelope surrounding the Earth, composed of 78% nitrogen, 21% oxygen, 0.9% argon, plus some carbon dioxide and water vapor. The atmosphere is divided into several layers, as follows: Troposphere: 0-10 miles Stratosphere: 10-50 miles Ionosphere: 50-370 miles Exosphere: 370 + miles Automatic Gain Control (AGC) A feature of some amplifiers and radio receivers which provides a substantially constant output even though the signal input varies over wide limits. Automatic Level Control (ALC) See Automatic gain control. Automatic Slope Control (ASC) A circuit that controls the slope of an amplifier automatically. See Slope. Avalanche Effect The cumulative multiplication of carriers in a semiconductor caused by an electric field across the barrier region strong enough so that electrons collide with valence electrons, releasing new electrons which have more collisions, which release more electrons, etc. Avalanche Photodiode (APD) A photodiode designed to take advantage of avalanche multiplication of photo-current. As the reverse-bias voltage approaches the breakdown voltage, hole-electron pairs created by absorbed photons acquire sufficient energy to create additional hole-electron pairs when they collide with substrate atoms; thus a multiplication effect is achieved. Amplification is almost noiseless, and this makes APD's 10 to 15 dB more sensitive than PIN photodiodes. The problems with APD's are: temperature sensitivity, high reverse bias voltages (200 to 400 V to achieve current multiplication of 100), and prices higher than PIN photodiodes. Axial Mode See longitudinal mode. Axial Ray A ray passing through the axis of the optical waveguide without any internal reflection. Azimuth Degrees clockwise from true north. For a compass heading a correction for local magnetic deviation is required. Azimuth-Elevation Mount Two pivot system consisting of separate azimuth and elevation adjustments for aiming a satellite antenna. Backscattering The scattering of light in a direction generally reverse to the original one. Balun Acronym for Balanced- Unbalanced. Refers to a 75 ohm to 300 OHM impedance matching transformer. Bandwidth 1. A range of frequencies (a portion of spectrum) defined by upper and lower frequency limits. 2. The capacity of an optical fiber to transmit information expressed in bits of information transmitted in a specific time period for a specific length of optical waveguide. Usually expressed like 10 megabits/sec/ km. Bandwidth is limited by pulse spreading or broadening due to dispersion, so that adjacent pulses overlap and cannot be distinguished. 3. The range of frequencies within which a fiber optic waveguide or terminal device performs at a given specification. Bandwidth-limited Operation The condition prevailing when the system bandwidth, rather than the amplitude (or power) of the signal, limits performance. The condition is reached when the system distorts the shape of the wave form beyond specified limits. For linear systems, bandwidth- limited operation is equivalent to distortion -limited operation. Beam Splitter A device that divides an incident beam into two or more separate beams. Prisms, thin films, sheets of glass, and partially silvered mirrors can be used to split a beam. Beat 1. To combine two carriers, so as to produce new sum and difference frequency carriers. 2. A carrier generated by two or more carriers which have been passed through a non-linear circuit. 81
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Functional Block Diagram - Blonder Tongue Laboratories Inc.

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