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| E-commerce | Business done over the Internet.
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| E layer | The layer of the ionosphere next to the D layer. This layer is weakly ionized and exists only in daylight.
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| EDGE (enhanced data for GSM evolution) | A faster 2.5G technology that used 8-PSKS modulation to achieve data rates up to 384 kbps.
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| Effective radiated power (ERP) | The power radiated by an antenna with directivity and therefore gain.
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| Electric field | An invisible force field produced by the presence of a potential difference between two conductors.
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| Electromagnetic field | A radio wave.
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| Electromagnetic interference (EMI) | Any interference to a communication device by any other electrical or electronic device.
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| Electromagnetic spectrum | The range of electromagnetic signals encompassing all frequencies.
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| Electromagnetic wave | A signal such as a radio signal made up of both electric and magnetic fields.
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| Electronic communication system | A group of devices including a transmitter, a channel or medium, and a receiver.
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| Electronic mail (E-mail) | The sending and receiving of electronic messages. Users create messages on their computers and send them to other users over a network.
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| Electrostatic discharge | The dissipation of a large electric field; lightning is an example.
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| Elevation | See Angle of elevation.
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| Encoding | A process in which binary data is transformed into a unique variation of the binary code, such as the Manchester code, prior to transmission.
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| Encryption | The process of encoding data in such a way as to obscure its meaning and content so that it can be transmitted securely.
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| End effect | A phenomenon caused by any support insulators used at the ends of a wire antenna. It causes a capacitance to be added to the end of each wire.
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| End-fire array | An antenna that uses two half-wave dipoles spaced one-half wavelength apart and has a bidirectional radiation pattern.
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| End of transmission block character (ETB) | A character transmitted to signal the end of a data block.
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| End of transmission character (EOT) | A character transmitted to signal the end of the data transmission.
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| Engineer | In the field of electronics, a person who holds a bachelor’s or an advanced degree and specializes in design.
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| Enhanced 911 (E911) capability | A feature included with 2.5G and 3G phones that is mandated by the U.S. government. This feature makes it possible to locate any cell phone position automatically.
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| Enhanced data for GSM evolution | See EDGE.
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| Envelope | An imaginary line connecting the positive peaks and negative peaks of the carrier wave form. The envelope gives the exact shape of the modulating information signal. Also, the outline of the peaks of individual signals like harmonics in the frequency spectrum.
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| Envelope delay | The time needed for a point on a waveform to pass through a filter.
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| Envelope detector | Another name for diode detector.
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| Equatorial orbit | A satellite orbit with an inclination of 0°.
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| Erbium-doped fiber amplifier (EDFA) | A type of optical amplifier.
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| Error | One or more incorrect bits in the transmission of information that is often caused by a very high noise level. It can be detected by special circuitry.
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| Error signal | The output of a phase detector circuit.
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| Ethernet LAN | Developed by Xerox Corporation, one of the oldest and one of the most widely used LAN types. It uses bus topology and baseband data-transmission methods.
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| Extended Binary Coded Decimal Interchange Code (EBCDIC) | An 8-bit code used mainly in IBM and IBM-compatible computing systems and equipment. It allows a maximum of 256 characters to be represented.
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| External noise | Random AC voltage that comes from sources over which we have little or no control—industrial, atmospheric, or space.
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| Extraterrestrial noise | An electrical disturbance that is solar or cosmic (from space).
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| Extremely high frequency (EHF) | The frequency range from 30 to 300 GHz.
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| Extremely low frequency (ELF) | The frequency range from 30 to 300 Hz.
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| Eye diagram | A diagram or pattern that is a display of overlapping individual bits of binary data displayed on a common oscilloscope.
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| F layer | The layer of the ionosphere closest to the sun. It is highly ionized, has the greatest effect on radio signals, and exists day and night.
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| F-type connector | An inexpensive coaxial connector used in TVs, VCRs, and cable TV.
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| Facsimile | An electronic system for transmitting graphical information by wire or radio.
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| Facsimile standards | Standards established by the International Telecommunications Union to ensure compatibility of fax machines made by different manufacturers.
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| Fading | A problem that occurs when radio waves pass through objects on their way from transmitter to receiver. The radio waves are negatively affected by these objects.
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| Far field | The radio wave beyond about one wavelength from the antenna.
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| Fast Ethernet | A newer version of Ethernet, currently the most widespread version of Ethernet. It has a speed of 100 Mbps. Also called 100Base-TX.
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| Fast Fourier transform (FFT) | A special version of the DFT algorithm developed to speed up the calculation of signal spectrum analysis.
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| Fast Fourier transform (FFT) spectrum analyzer | A test instrument that gives a frequency domain display similar to other types of spectrum analyzers.
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| Ferrite disk | A ceramic, sometimes made of yttrium-iron-garnet (YIG), used in circulators.
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| FET mixer | A mixer that uses the square law response of a field-effect transistor for frequency conversion.
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| FET phase modulator | A modulator with a phase shifter made up of a capacitor and the variable resistance of a field-effect transistor.
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| Fiber digital data interface (FDDI) | A high-speed fiber-optic cable network offering a data transmission rate of 100 Mbps.
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| Fiber-optic cable | A nonconducting cable consisting of a glass or plastic center cable surrounded by a plastic cladding encased in a plastic outer sheath and used in optical communication systems. It acts as a light “pipe.”
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| Fiber-optic communication system | A communication system that uses electronic digital and optical multi-plexing techniques for high speed data communication.
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| Fiber-optic connector | A connector designed to provide a fast and easy way to attach or remove fiber-optic cables.
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| Fiber-optic interrepeater link (FOIRL) | A fiber-optic communication channel with repeaters at each end that are designed to interconnect two Ethernet networks.
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| Fibre Channel (FC) | An optical fiber transmission standard with speeds to 2 Gbps used primarily in storage area networks (SANs).
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| Fibre Distributed Data Interface (FDDI) | A LAN standard designed to connect up to 500 nodes (PCs, etc.) in a ring configuration over a distance of up to 60 miles.
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| Field | In the generation of a video signal, one complete scanning of a scene, which contains 2621⁄2 lines.
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| Field strength meter (FSM) | A portable device used for detecting the presence of RF signals near an antenna.
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| File transfer | The transfer of files, records, or whole databases from one place to another.
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| Filter | A frequency-selective circuit designed to pass some frequencies and reject others.
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| Filtering | The use of circuits to separate frequencies.
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| Final power amplifier | The high-power amplifier that drives to an antenna or other load in an RF system.
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| Finite impulse response (FIR) filter (nonrecursive filter) | A popular DSP filter whose output is a function of the sum of products of the current input samples.
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| Firewall | A piece of software that monitors all incoming data to a network for the purpose of establishing whether the data meets the standards or guidelines set by an organization or individual for admission to the network and computers.
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| Flash converter | A fast analog-to-digital converter that uses a large resistive voltage divider and multiple analog comparators.
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| Flicker noise | An electrical disturbance that occurs in resistors and conductors and is the result of minute random variations of resistance in the semiconductor material.
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| FM/FM system | A system that uses the FM of the VCO subcarriers as well as the FM of the final carrier in a telemetry system.
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| Folded dipole | A variation of the half-wave dipole consisting of two parallel conductors connected at the ends with one side open at the center.
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| Forward AGC | A method of reducing gain by increasing the collector current.
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| Forward error correction (FEC) | The process of detecting and correcting errors at the receiver so that retransmission is not necessary.
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| Forward (incident) power | The power sent down a transmission line toward the load.
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| Foster-Seeley discriminator | One of the earliest FM demodulators, no longer widely used.
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| Fourier theory | The process for accurately analyzing and expressing complex nonsinusoidal signals in terms of harmonics using calculus.
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| Frame | The portion of a packet that contains the data to be communicated plus addressing and error detection codes.
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| Frame rate | The number of frames transmitted in 1 second.
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| Frame relay | A packet switching system used by the major telecommunications companies for data transfer.
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| Free-running frequency | The normal operating frequency of a VCO, as determined by internal frequency-determining components.
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| Frequency | In electronics, the number of cycles of a repetitive wave that occur in a given period of time.
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| Frequency conversion | The process of translating a signal to a higher or lower frequency while retaining the originally transmitted information.
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| Frequency-correcting network, predistorter, or 1/f filter | A low-pass filter that causes the higher modulating frequencies to be attenuated.
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| Frequency counter | A test instrument that measures signal frequency.
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| Frequency deviation (fd) | The amount of change in carrier frequency produced by the modulating signal.
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| Frequency demodulator | A circuit used to recover the original modulating signal from an FM transmission.
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| Frequency divider | A circuit with an output frequency that is some integer submultiple of the input frequency.
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| Frequency division multiplexing (FDM) or frequency division multiple access (FDMA) | A type of multiplexing in which multiple signals share the bandwidth of a common communication channel.
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| Frequency-domain display | A plot of signal amplitude versus frequency.
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| Frequency-hopping (FH) SS | A type of spread spectrum in which the frequency of the carrier of the transmitter is changed according to a predetermined sequence at a rate less than the serial binary data modulating the carrier.
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| Frequency modulation | Modulation in which the instantaneous frequency of the modulated waves differs from the carrier frequency by an amount proportional to the instantaneous value of the modulating wave.
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| Frequency modulator | A circuit that varies carrier frequency in accordance with the modulating signal.
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| Frequency multiplier | A circuit with an output frequency that is some integer multiple of the input frequency.
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| Frequency-multiplier diode | A diode designed primarily for frequency-multiplier service. Varactor diodes and step-recovery diodes are frequency-multiplier diodes.
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| Frequency reuse | A technique used for effectively increasing the bandwidth and informa-tion-carrying capacity of a satellite. A means by which cells within a cellular telephone system can share the same frequency channel. Seealso Spatial multiplexing.
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| Frequency-shift keying (FSK) | A type of modulation widely used in the transmission of binary data. Used primarily in low-speed modems, FSK uses two sine-wave frequencies that represent binary 0s and 1s.
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| Frequency spectrum | The electromagnetic spectrum.
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| Frequency synthesizer | A signal-generating circuit whose output can be changed in discrete increments by digital means.
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| Friis’s formula | The formula used to calculate the overall noise performance of a receiver or of multiple stages of RF amplification.
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| Front-to-back (F/B) ratio | The ratio of the power radiated in the forward direction to the power radiated in the backward direction.
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| Function generator | A signal generator that generates sine waves, square waves, and triangular waves over a frequency range of about 0.001 Hz to about 2 MHz.
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| GaAsFET | A junction field-effect transistor made with gallium arsenide. See also Gallium arsenide.
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| Gain | Amplification. The ratio of output to input of an amplifier, circuit or antenna.
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| Gallium arsenide (GaAs) semiconductor | A compound semiconductor used in microwave transistors and LEDs made specifically for fiber-optic applications. It emits light at 1.3 mm.
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| GASFET | Another name for MESFET.
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| Gateway | An internetwork device that acts as an interface between two LANs or between a LAN and a larger computer system. This two-way translator allows different types of systems to communicate.
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| Gaussian filtered MSK (GMSK) | A method of prefiltering MSK in which harmonic content and overall signal bandwidth are reduced.
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| General packet radio service | See GPRS.
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| Geocenter | The center of the earth.
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| Gigabit Ethernet | The most recent version of Ethernet, capable of achieving 1000 Mbps or 1 Gbps over Category 5 UTP or fiber-optic cable. Also called 1000Base-T Ethernet.
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| Gilbert transconductance cell | The balanced mixer made with transisters and used in most IC mixers.
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| Global Positioning System (GPS) | Satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth.
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| Global System for Mobile Communications | See GSM.
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| GPRS (general packet radio service) | The most popular 2.5G technology, designed to work with GSM phones. It transmits data as well as digitized voice.
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| GPS receiver | A complex superheterodyne microwave receiver designed to pick up GPS signals, decode them, and compute the location of the receiver.
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| Graded index cable | A cable whose index of refraction for the core varies smoothly and continuously over the diameter of the core.
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| Grid | A control element added between the plate and the cathode of a vacuum tube to control the current flow.
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| Ground | The common reference point for most voltages in a circuit.
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| Ground control equipment (GCE) subsystem | Equipment at a satellite earth station, which is used for demodulating and demultiplexing the received signals.
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| Ground loop | An unintentional circuit that occurs when multiple circuits or pieces of equipment are connected to a common ground at different points.
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| Ground plane | A conducting surface or array of conductors over 1⁄4 llong used as one element in a vertical antenna. The earth becomes known as the ground plane once a good electrical connection to earth has been made.
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| Ground-plane antenna. | See Marconi vertical antenna.
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| Ground station | Also known as an earth station, the terrestrial base of the satellite communication system.
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| Ground wave | A wave that follows the curve of the earth and can therefore travel to distances beyond the horizon.
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| Groupware | A set of programs that allow two or more individuals working on a single project to share databases, exchange messages, manage work flow, and maintain a calendar.
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| GSM (Global System for Mobile Communications or Group Special Mobile) | The most widely used 2G digital phone system.
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| Gunn diode | A thin piece of N-type gallium arsenide (GaAs) or indium phosphide (InP) semiconductor which forms a resistor when voltage is applied to it. Also called transferred-electron device (TED). Uses its negative resistance characteristics to generate a microwave signal.
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| Gyrotron | The only device available for power amplification and signal generation in the millimeter-wave range.
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| Hamming code | A popular method of forward error correction (FEC), a code that uses extra bits added to a transmitted word and processed to identify and correct bit errors.
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| Handoff | A switching at the mobile telephone switching office (MTSO) from a weaker cell to a stronger cell, to provide optimum transmission and reception.
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| Handset | The portion of a telephone that contains the speaker and microphone, which serve as transmitter and receiver.
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| Handshaking | The exchange of status information between transmitter and receiver in a digital system.
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| Harmonic | A sine wave whose frequency is some integer multiple of a fundamental sine wave.
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| Hartley’s law | A law that states that the greater the bandwidth of a channel, the greater the amount of information that can be transmitted in a given time.
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| Harvard architecture | A type of microprocessor in which there are two memories: a program or instruction memory and a data memory. There are two data paths between the memories.
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| Hash function or algorithm | A simple method of encryption that converts a plaintext message into a compressed binary number representing that data.
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| Helical antenna | A wire helix in which the diameter of the helix is typically one-third wavelength. Spacing between turns is about one-quarter wavelength.
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| Hertz antenna | See Dipole antenna.
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| Heterodyne processing | A method of translating the incoming TV signal to a different frequency.
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| Heterodyne processor | A module used by cable companies to translate receiver signals to the desired channel.
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| Heterodyning | The function performed by a mixer circuit in frequency conversion.
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| Heterojunction bipolar transistor (HBT) | A transistor that makes high-frequency amplification possible in both discrete form and integrated circuits. It is formed with two different types of semiconductor materials.
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| High-definition TV (HDTV) or digital TV (DTV) | System that transmits fine picture detail and enhanced sound.
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| High electron mobility transistor (HEMT) | A variant of the MESFET that extends the frequency range beyond 20 GHz by adding an extra layer of semiconductor material.
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| High frequency (HF) | The frequency range from 30 to 300 MHz.
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| High-level AM | A variation of voltage and power in the final RF amplifier stage of a transmitter.
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| High-level data link control (HDLC) protocol | A popular modulation technique used in modems for increasing the number of bits per baud.
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| High-pass filter | A filter that passes frequencies above the cutoff but rejects frequencies below it.
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| High-power amplifier (HPA) | An amplifier used to increase signal level.
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| High-Speed Token Ring (HSTR) | A new version of Token Ring that runs at 100 Mbps.
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| Horn antenna | An antenna created by flaring the end of the waveguide. The more gradual the flair, the better the impedance match and the lower the loss.
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| Hot carrier diode | Also known as a Schottky diode, this diode is made with N-type silicon on which is a thin metal layer.
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| Hub | A LAN accessory that functions like a central connecting box. It is designed to receive the cable inputs from various PC nodes and connect them to the server.
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| Huygens’ principle | The principle based on the assumption that all electromagnetic waves radiate as spherical wavefronts from a source. When the waves encounter an obstacle, they pass around it, above it, and on either side of it.
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| Hybrid circuit | A popular form of MMIC that combines all amplifier ICs connected to microstrip circuits and discrete components of various types. Also, a special transformer used to convert signals from the four wires of a transmitter and receiver into a signal suitable for a single two-line pair to the local loop.
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| Hybrid fiber cable (HFC) system | A newer system of cable TV in which a fiber-optic cable and a coaxial cable rather than just a coaxial cable is used.
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| Hybrid ring | A special form of microstrip with four taps or ports on the line spaced at one-quarter wavelength intervals which can be used as inputs or outputs.
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| Hybrid T | A waveguide-like device with combined series and shunt T sections that is used to permit simultaneous use of an antenna by both a transmitter and a receiver.
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| Hypertext | On the Web, a method that allows different pages or sites to be linked.
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| Hypertext transfer protocol (http) | The first part of a URL. It specifies the communication protocol to be used.
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| I and Q | The in-phase and quadrature signals used in most digital modulation and demodulations circuits.
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| I color signal | A TV color signal with the following specifications: 60 percent red, 28 percent green, and 32 percent blue.
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| IC balanced modulator | A balanced modulator circuit using differential amplifiers.
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| IC electronic telephone | A telephone unit in which all the circuits are fully integrated on a single chip of silicon.
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| IC receiver | An integrated circuit radio receiver. A receiver on a single chip.
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| IF amplifier | An amplifier that uses tuned circuits with crystal, ceramic, or SAW filters in order to provide good selectivity. Seealso Intermediate frequency.
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| Image | An interfering RF signal that is spaced from the desired incoming signal by a frequency that is two times the intermediate frequency above or below the incoming frequency.
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| Image processing | The processing of data by algorithms that are used to improve the resolution clarity, speed, or signal-to-noise ratio of a transmitted picture.
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| Image reject mixer | A special type of mixer used in designs in which images cannot be tolerated.
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| IMPATT diode | A PN-junction diode that is made of silicon, GaAs, or InP and operates with a high reverse bias that causes it to avalanche, or break down. It is available with power ratings to about 25 W and to frequencies as high as 30 GHz.
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| Impedance | The total opposition of the components produced by combining resistance, inductance and/or capacitance in series or parallel.
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| Impedance matching | A procedure done to ensure that maximum power transfer will take place between a transmitter or receiver and an antenna with transmission line.
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| Impedance-matching network | A circuit used to transfer maximum signal power from one circuit to another.
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| Impedance-matching pad | A resistive T network that provides the correct match between the receiver and input and the generator.
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| Impedance meter | An instrument (often bridge type) that accurately measures the impedance of a circuit, a component, or an antenna at RF frequencies.
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| Impedance of space | See Wave impedance.
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| Incident power | See Forward power.
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| Incident ray | Light ray from a light source. The input wave from a generator to the end of a fiber-optic transmission line.
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| Index of refraction | A figure obtained by dividing the speed of a light wave in a vacuum by the speed of a light wave in a medium that causes the wave to be bent. The ratio of the speed of light in air to the speed of light in the substance.
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| Indirect FM | The FM produced by a phase modulator.
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| Indium phosphide (InP) semiconductor | A compound semiconductor material made with indium and phosphorus.
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| Inductor | An electronic component made by winding multiple turns of a wire on a form. Also called a coil or choke.
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| Industrial noise | Electrical disturbance created by manufactured equipment such as automotive ignition systems, electric motors, and generators.
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| Infinite impulse response (IIR) filter (recursive filter) | A recursive DSP filter that uses feedback. Each new output sample is calculated using both the current output and past samples.
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| Information | In electronic communication systems, the message or data.
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| Infrared communication | A form of optical communication that utilizes signals from 0.7 to 1000 mm.
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| Infrared LAN | The least expensive form of wireless LAN. It uses infrared transceivers.
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| Infrared (IR) wireless | The use of infrared light for short-distance data communication.
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| Infrared spectrum | The region of the optical spectrum just below visible light, from 0.7 to 1000 mm.
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| Injection laser diode (ILD) | A PN-junction diode usually made with GaAs. It produces a low-level light over a broad frequency range with a low-level forward-biased current.
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| Insertion loss | The loss a filter introduces to the signals in the passband (usually in decibels). Passive filters introduce attenuation because of resistive losses in the components and the voltage divider effect.
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| Institute of Electrical and Electronics Engineers (IEEE) | A professional society that establishes and maintains a wide range of electrical, electronic, and computing standards.
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| Instrumentation subsystem | An extension of a satellite telemetry system; a general term for all the electronic equipment used to deal with the information transmitted back to the earth station.
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| Integrated circuit | Seeentriesunder IC.
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| Integrated services digital network (ISDN) system | A digital communication interface designed to replace the local analog loop used in the public switched network but rarely used.
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| Intensity modulation | A type of modulation used when the information or intelligence signal controls the brightness of a laser transmitter. A form of amplitude modulation.
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| Interexchange carriers (IXCs) | Long-distance telephone service carriers.
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| Interlaced scanning | The meshing of two sequentially scanned fields on a TV CRT.
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| Intermediate frequency (IF) | The lower frequency to which superheterodyne receivers convert all incoming signals. The mixer output of a superheterodyne receiver, it is the difference between the input signal frequency component and the local oscillator frequency.
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| Intermediate-power amplifier (IPA) | An amplifier in a chain of several amplifiers used to boost the power level of a signal before transmission. The amplifiers are usually referred to as low-power, intermediate-power, and high-power amplifiers.
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| Intermodulation distortion | Distortion resulting from the generation of new signals and harmonics arising from circuit nonlinearities.
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| Intermodulation products | The unintentional mixing of signals and harmonics to produce undesired interfering signals.
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| Internal noise | Noise caused by heat in electronic components in a receiver such as resistors, diodes, and transistors.
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| International Organization for Standardization | An organization that has developed a framework, or hierarchy, known as the open systems interconnection model, that defines how data can be communicated.
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| International Telecommunications Union (ITU) | An agency of the United Nations whose duties include setting standards for various areas within the communication field. Formerly known as the CCITT, it establishes standards to ensure compatability of telecommunication equipment of different manufacturers.
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| Internet | A worldwide connection of computers by means of a complex network of many networks.
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| Internet backbone | A collection of worldwide networks of high-speed fiber-optic cable that carry all Internet traffic.
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| Internet Engineering Task Force (IETF) | An organization that develops and standardizes technologies and protocols related to Internet data transfer.
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| Internet service provider (ISP) | A company set up especially to tap into the Internet.
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| Interoperability | The ability of equipment from one manufacturer to work compatibly with that of another.
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| Intersymbol interference (ISI) | Pulses that blur into one another cause this type of interference. The longer the cable or the higher the bit rate, the greater the distortion.
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| Ionosphere | The region of the upper atmosphere where ultraviolet radiation from the sun causes the atmosphere to become electrically charged, or ionize.
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| IP address | Internet protocol address. A 32-bit binary number assigned to a specific computer to identify its presence on the Internet to a router.
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| IPv4 (Internet Protocol version 4) | The currently most widely used IP protocol. Its destination address size, 32 bits, limits the number of users. IPv4 will be replaced by IPv6 that uses a 128-bit address.
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| IrDA system | The most widely used IR data communication system.
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| Iridium system | An advanced satellite cellular telephone system that uses a constellation of 66 satellites in six polar orbits with 11 satellites per orbit 420 miles above the earth.
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| iSCSI | Internet Small Computer Systems Interface (SCSI). A version of the popular SCSI parallel data interface used to connect hard drives and tape drives to computers that uses Ethernet for connectivity.
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| IS-95 CDMA | A TIA cell phone standard, also known as CDMA One, which uses spread spectrum.
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| IS-136 TDMA | The Telecommunications Industry Association (TIA) standard that describes the TDMA cell phone system.
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| Isolator | A type of circulator with one input and one output.
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| Isotropic radiator | A theoretical point source of electromagnetic energy.
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| Jacket | The protective insulation that surrounds the core of a cable with its cladding.
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| JBOD | Just a bunch of disks Term used to describe a collection of hard disk drives used externally for a computer or server to store massive amounts of data.
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| Jitter | A type of noise that shows up as a time variation of the leading and trailing edges of a binary signal.
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| Kermit protocol | A once popular asynchronous protocol that requires that every packet that is sent be acknowledged by the receiver as read correctly.
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| Key | A secret binary number used in the encryption process that must be known or exchanged to decrypt the data.
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| Key system | A small telephone system designed to serve from 2 to 50 user telephones within an organization.
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| L network | An inductor and a capacitor connected in various L-shaped configurations used for impedance matching.
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| Laser | A single-frequency light source that produces a very narrow beam of brilliant light of a specific wavelength.
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| Laser diode | PN-junction diode usually made with a GaAs compound that produces coherent laser light. It is the most widely used light source in fiber-optic systems.
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| Laser transmitter | The circuitry associated with the laser in a fiber-optic transceiver.
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| Latitude | The angle between a line from a given point on the surface of the earth to the geocenter and the line between the geocenter and the equator.
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| Lattice modulator | See Diode ring.
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| Law of reflection | This law states that the angle of incidence is equal to the angle of reflection.
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| LC filter | A filter made with inductors and capacitors.
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| LC oscillator | A signal-generating circuit whose frequency is set by an inductor-capacitor combination. Colpitts, Hartley, and Clapp circuits are examples of this type of oscillator.
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| LED transmitter | A type of transmitter employing a light-emitting diode that is used for short-distance, low-speed, digital fiber-optic systems.
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| Left-hand circular polarization (LHCP) | The term that describes radiation which leaves an antenna with a counterclockwise rotation.
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| Light | A type of electromagnetic radiation that occupies the part of the frequency spectrum lower in frequency than x-rays but higher in frequency than microwaves and includes infrared, visible, and ultra-violet light.
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| Light detector (photocell) | A light-sensitive device that converts light pulses into an electrical signal.
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| Light-emitting diode (LED) | A PN-junction semiconductor device that emits light when forward-biased.
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| Light receiver | A type of receiver in which current through the photodiode, generated when light is sensed, produces a current that is amplified in an op amp.
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| Light transmitter | A laser or LED and its associated driving circuitry.
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| Limiter | A circuit used to remove any amplitude variations on the FM signal before the signal is applied to the demodulator.
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| Linear amplifier | An amplifier that provides an output that is an identical, enlarged replica of the input. An amplifier whose output is a straight line function of its input.
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| Line-of-sight communication | A communication signal that travels in a straight line directly from the transmitting antenna to the receiving antenna.
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| Loading coil | A series inductor used to bring a short antenna into resonance at the desired frequency.
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| Local access and transport areas (LATAs) | Designated geographical areas to which local exchange carriers (LECs) provide telephone services.
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| Local-area network (LAN) | An information network that transmits data from one place to another using some form of cable or wireless communication signal. A group of PCs in an office or company that are connected in order to share data and other resources.
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| Local exchange | See Central office.
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| Local exchange companies (or carriers; LECs) | Companies to which local exchanges that provide local telephone service are connected.
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| Local loop (subscriber loop) | A two-wire, twisted-pair connection between a telephone and the central office.
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| Local oscillator | Either a conventional LC tuned or crystal oscillator or a frequency synthesizer used to produce a continuous sine wave. Usually drives a mixer in a receiver.
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| Lock range | The range of frequencies over which a PLL can track an input signal and remain locked.
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| Log-periodic array | An antenna in which the lengths of the driven elements vary and are related logarithmically. This type of antenna also provides a very wide bandwidth as well as gain and directivity.
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| Long-distance operation | Service offered by interexchange carriers that provide the interconnection for any inter-LATA connections
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| Longitudinal redundancy check (LRC) | The process of logically adding, by exclusive ORing, all the characters in a specific block of transmitted data used for error detection.
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| Loran system | A highly accurate marine navigation satellite system using coastal stations along U.S. water borders.
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| Losses | Attenuation or weakening of a signal in a circuit, coaxial, or fiber-optic cable.
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| Low frequency (LF) | The frequency range from 30 to 300 kHz.
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| Low-level AM | Amplitude modulation at a low power level that must be amplified by a linear amplifier considerably before being transmitted.
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| Low-noise amplifier (LNA) | An RF amplifier that uses special low-noise transistors to provide initial amplification in a receiver.
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| Low-pass filter | A circuit that introduces no attenuation at frequencies below the cutoff frequency but greatly attenuates all signals with frequencies above the cutoff.
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| Luminance (Y ) signal | The signal that results when different levels of light along each scan line are transmitted as shades of gray between black and white.
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