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F connector - A standard 75-ohm connector used on coaxial cable.

F-number - The f-number indicates the brightness of the image formed by the lens, controlled by the iris. A smaller f-number means a brighter image.

F-stop - A term used to indicate the speed of a lens. The smaller the f-number, the greater is the amount of light passing through the lens.

F/UTP - Foil applied over unshielded twisted pairs.

Facility – (1) In general, a feature or capability offered by a system, item of hardware or software. (2) In Telco environments, line and equipment used to furnish ac completed circuit. See NETWORK FACILITIES.

Facility equipment room - A room or wiring closet used to store extended networking components that link one building with another building. These products include remote bridges and remote repeaters as well as X.25 gateways and Decent wide-area network routers.

Facsimile - The remote reproduction of graphic material: an exact copy.

Farad - A unit of capacitance when a difference of potential of one volt produces a displacement of one coulomb in a capacitor. The farad is a very large unit and a much smaller unit, the microfarad (μf), is more commonly used.

FAT (file allocation table) - A record, generated by DOS, that keeps track of where each file is on a disk, which sectors of the disk are in use and which sectors are available for new data to be written to them.

Fatigue resistance - Resistance to metal crystallization, which leads to conductors or wires breaking during flexing.

Fault - An unintentional, low-resistance connection between two or more conductors, or an open or broken conductor.

Fault ground - A fault to ground.

FCC (Federal Communications Commission) - Has the authority to regulate all interstate communications originating in the United States. It is run by seven board members appointed by the President. It sets prices for interstate phone, data and video service; determines who can or cannot get into the business of providing telecommunications service or equipment in the U.S.; and determines the electrical and physical standards for telecommunications equipment.

FDDI (fiber distributed data interface) - An ANSI defined token-passing ring using optical fiber media to attain a 100 Mbps transmission rate.

FDM (frequency division multiplexing) - Method by which the available transmission frequency range is divided into narrower bands, each used for a separate channel. As used by broadband technology, the frequency spectrum is divided up among discrete channels to allow one user or a set of users access to single channels.

FDMA - Frequency division multiple access.

FEXT (far-end crosstalk) - Unwanted signal coupling from a transmitter at the near end into a neighboring pair measured at the far end.

FDX (full-duplex) - Transmission in two directions simultaneously or, more technically, bi directional, simultaneous two-way communications.

Feeder cable - An intermediate cable distribution line in a broadband coaxial network that branches off a main trunk cable.

Femto - A prefix meaning 0.000000000000001 (10-15).

FEP - (Teflon) DuPont trademark for Fluorinated Ethylene Propylene. Front-end processor.

FEPB - A UL cable type. Fluorinated ethylene propylene insulated wire with glass braid. 14 AWG to 2 AWG, 90°C dry/damp or 200°C dry maximum operating temperature.

FDDI - Fiber distributed data interface.

FDM - Frequency division multiplexing.

FDX - Full duplex.

FEXT - Far-end crosstalk.

FFH-2 - A UL type of heat-resistant rubber-covered fixture wire with flexible stranding. 600 V rating, 18 AWG–16 AWG, 75°C maximum operating temperature.

Fiber dispersion - Pulse spreading in an optical fiber caused by differing transit times of various modes (a mode is one ray of light).

Fiber backbone - See BACKBONE.

Fiber optic cable - See OPTICAL FIBER.

Fiber optics - Transmission of energy by light through glass fibers. A technology that uses light as an information carrier. Optical fiber cables (light guides) are a direct replacement for conventional coaxial cable and wire pairs. The glass-based transmission cable occupies far less physical volume for an equivalent transmission capacity; the fibers are immune to electrical interference.

Fiber tubing - A loose, crush-resistant cylinder applied over individual fibers to provide mechanical protection. Also called a buffer tube.

Field - One half of a frame, consisting of either the odd or the even numbered lines, 60 fields are transmitted every second.

Field coil - A suitable insulated winding mounted on a field pole to magnetize it.

Field molded splice - A joint in which the solid dielectric joint insulation is fused and cured thermally at the job site.

Field tests - Tests that may be made on a cable system after installation as an acceptance or proof test. Various standards with test recommendations exist, like IEEE 400.

Figure 8 cable - An aerial cable configuration in which the conductors and the steel strands that supports the cable are integrally jacketed. A cross section of the finished cable approximates the figure “eight.”

File - A collection of related data records.

File server - A station dedicated to providing file and mass data storage to the other stations on the local network.

Filled cable - A cable construction in which the cable core is filled with a material that will prevent moisture from entering or passing through the cable.

Filler - Fillers are used in multi-conductor cables that occupy the interstices formed by the assembled conductors. This is done so that the finished cable will be round.

Filling compound - A dielectric material poured or otherwise injected into a splice housing to prevent the entry of water. Filling compounds may require heating or mixing prior to filling. Some filling compounds may also serve as the insulation.

Filter - An arrangement of electronic components designed to pass signals in one or several frequency bands and to attenuate signals in other frequency bands.

Fine stranded wire - Stranded wire with component strands of 36 AWG or smaller.

Flame resistance - The ability of a material to not propagate flame once the heat source is removed.

Flammability - The measure of a material’s ability to support combustion.

Flange black - The distance from the flange of the lens (beginning of the lens mount) to the focal plane. C mount lenses have a flange back distance of 17.526 mmv s. 12.5 mm for CS mount.

Flashover - A disruptive discharge around or over the surface of a solid or liquid insulator.

Flat braid - A woven braid of tinned copper strands rolled flat at the time of manufacture to a specified width.

Flat cable - A cable with two essentially flat surfaces.

Flat conductor - A wire having a rectangular cross section as opposed to a round or square conductor.

Flat loss - Equal signal loss across the system’s entire bandwidth.

Flex-life - The measurement of the ability of a conductor or cable to withstand repeated bending usually specified as expected total number of cycles before failure.

Flexibility - The ease with which a cable may be bent. In general, finer stranding gives greater flexibility. Various types of cables are available depending on the type of flexing required.

Flexible - That quality of a cable or cable component that allows for bending under the influence of an outside force, as opposed to limpness that is bending due to the cable’s own weight.

Floating - Refers to a circuit that has no electrical connection to ground.

Flooded cable - A special coaxial cable that contains a corrosion resistant gel between the outer aluminum sheath and the outer jacket. The gel flows into imperfections in the jacket to prevent corrosion in high-moisture areas.

Flow control - The capability of network nodes to manage buffering schemes in order to allow devices of differing data transmission speeds to communicate with each other.

Fluoropolymer - A class of polymers used as insulating and jacketing materials. Common ones include Teflon, Tefzel, Kynar and Halar.

Flux - (1) The lines of force which make up an electrostatic field. (2) The rate of flow of energy across or through a surface. (3) A substance used to promote or facilitate fusion, commonly used in soldering.

FM (frequency modulation) - A modulation technique in which the carrier frequency is shifted by an amount proportional to the value of the modulating signal. The amplitude of the carrier signals remains constant. The deviation of the carrier frequencies determines the signal content of the message.

Foamed insulation - Insulations having a cellular structure.

Focal length - The distance from the center of the lens to a plane at which point a sharp image of an object viewed at an infinite distance from the camera is produced. The focal length determines the size of the image and the angle of the field of view seen by the camera through the lens. That is the distance from the center of the lens to the pickup device.

Focis - Fiber Optic Connector Intermateability Standard.

Foil - A thin, continuous sheet of metal. Often used as a shield material in cables.

FOIRL (Fiber Optic Inter-Repeater Link) - An optical fiber signaling methodology based in the proposed IEEE 802.3 standard governing optical fiber and the FDDI standard.

Foot-candle – It is the light intensity (illumination) of a surface one foot distant from a source of one candela. It is equal to one lumen per square foot. (1FC = 1 lmf t.2). The foot-candle is the unit used to measure incident light.

Forward direction - The direction on the cable from the head end to the modems.

Four-wire circuit, four-wire line - A circuit using two pairs of conductors, one pair for the transmit channel and the other pair for the receive channel. All long distance circuits are four-wire. Almost all local phone lines are two wires. All analog phones are two wires. Four-wire circuits offer much higher quality.

Frame - 1. The total area of the picture that is scanned while the picture signal is not blanked. 2. Same as transmission block. 3. The sequence of bits and bytes in a transmission block. 4. The overhead bits and bytes that surround the information bits in a transmission block. 5. The unit of transmission in some local area networks, including the IBM token-ring network. It includes delimiters, control characters, information and checking characters. A frame is created from a token when the token has data appended to it.

Framing - Process of inserting control bits to identify channels; used in TDM signals.

Frequency - The number of cycles per second, at which an analog signal occurs, expressed in hertz (Hz). One hertz is one cycle per second.

Frequency analyzer - An instrument to measure the intensity of various component frequencies from a transmitting source.

Frequency counter - An electronic measuring instrument that precisely counts the number of cycles of a periodic electrical signal during a given time interval.

Frequency deviation - A swing away from the nominal frequency.

Frequency division multiplexing - The splitting of a communications line into separate frequency bands, each capable of carrying information signals. This allows several messages to be sent at the same time over the same transmission medium.

Frequency Modulation (FM) - Method of encoding a carrier wave by varying the frequency of the transmitted signal.

Frequency plan - Specification of how the various frequencies available in a communications system are allocated for use. In the U.S. the FCC defines uses for various frequency bands.

Frequency range - The frequency spectrum allocated for use by any frequency selective device or component.

Frequency response - The variation of gain or attenuation with frequency.

Front porch - The portion of the composite video signal that lies between the leading edge of the horizontal blanking pulse and the leading edge of the corresponding synchronizing pulse.

FSMA (fiber subminiature assembly) - It is a threaded connector for multimode optical fiber cables.

FSO (free space optics) - Refers to the transmission of modulated visible or infrared (RI) beams through the atmosphere to obtain optical communications. Like fiber, free space optics (FSO) uses lasers to transmit data, but instead of enclosing the data stream in a glass fiber, it is transmitted through the air.

FTTD® - Anixter registered trademark meaning fiber to the desk.

FTTH - Fiber to the home.

FTTP - Fiber to the premises.

Full duplex - Two-way communications in which each modem simultaneously sends and receives data at the same rate.

Fuse wire - Wire made from an alloy that melts at a relatively low temperature to open a circuit when over-current conditions occur.

Fused coating - A metallic coating that has been melted and solidified, forming a metallurgical bond to the base material.

Fused conductors - Individual strands of heavily tinned copper wire stranded together and then bonded together by induction heating.

Fused spiral tape - A PTFE insulation often used on hook-up wire. The spiral wrapped tape is passed through a sintering oven where the overlaps are fused together.