Fatigue Resistance -- Resistance to metal crystallization which leads to conductors or wires breaking from flexing.

Feedback -- The returning of a fraction of the output of an electric oscillation to the input.

Feeder Cable -- In a CATV system, the transmission cable from the head end (signal pickup) to the trunk amplifier; also called a trunk cable.

Ferrous -- Material composed of and/or containing iron. A ferrous metal exhibits magnetic characteristics as opposed to a non-ferrous metal, such as aluminum, which does not.

Fiber -- A single, separate optical transmission element characterized by core and cladding.

Fiber Dispersion (Fiber Optic) -- Pulse spreading in a fiber caused by differing transit times of various modes.

Fiber Optics -- Light transmission through optical fibers for communication and signaling.

Fiber Tubing (Fiber Optic) -- A loose crush-resistant cylinder applied over individual fibers to provide mechanical protection.

Fiberglass -- A trademark name for glass which is formed into thin fibers. When twisted and plied into yarns, it is used to form a braid covering for wire and cable. Normally saturated with silicone-base varnish to prevent passage of moisture and fraying of fibers.

Field -- The area through which pass electric and/or magnetic lines of force.

Field Strength -- The strength of an electromagnetic field. The measurement may be either the electric of the magnetic component of the field and may be expressed as V/m, A/m; any one of these may be converted to the others.

Figure 8 Cable -- An aerial cable configuration in which the conductors and steel strand which supports the cable are integrally jacketed. A cross-section of the finished cable approximates the figure "eight".

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

Filler -- Various material cabled with insulated conductors to achieve roundness, strength or flexibility. Fillers are used in multi-conductor cables to occupy the interstices formed by the assembled conductors. Filler is also a substance, often inert, added to a plastic to improve properties and/or decrease cost.

Flame Resistance -- The ability of a material to extinguish flame once the source of heat is removed.

Flammability -- The measure of the material's ability to support combustion.

Flat Braid -- A woven braid, composed of tinned copper strands, which is rolled flat at time of manufacture to a specific width depending upon construction. It is generally used as a high current conductor at low voltages.

Flat Conductor -- A wire manufactured in a flattened form as opposed to round, or square, conductors.

Flex Life -- The time of heat aging that an insulating material when bent around a specific radius can withstand before failure. Flex life is used to evaluate thermal endurance.

Flexural Strength -- The strength of a material in bending.

Floating -- Referring to a circuit which has no connection to ground.

Flow -- The movement of a conductor within an insulating or dielectric material.

Fluorinated Ethylene Propylene (FEP) -- A homopolymer of ethylene and propylene. This high temperature resin is well suited for wire insulations and jackets for plenum applications. It can withstand an unusual amount of physical abuse during and after installation, has very good electrical characteristics, good thermal and low temperature properties and chemical inertness.

Fluorocarbons -- Resins which include fluorine in their molecular structure; the greater the fluorine content, the better are the polymer's electrical, mechanical, thermal and chemical properties. Polyvinylidene fluoride (PVDF), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP) and ethylene chlorotrifluoroethylene (ECTFE) are common wire insulations and jackets from the fluorocarbon family used for plenum wiring applications. PVDF is used primarily for jacketing purposes only. Also see Fluoropolymer.

Fluoropolymer -- Family of polymers of general paraffinic structure which have some or all of the hydrogen replaced by fluorine. Polymer has characteristics that will pass stringent flammability tests making them desirable for jacket and conductor insulations for inside cables placed in commercial building plenum areas.

Flux -- (1) A material that helps produce fusion, as solder flux. (2) A continuous flowing or passing, as in the field created by a magnet.

Foam Filled Cable -- A jelly filled (polyethylene modified petrolatum) outside plant cable utilizing foamed polyolefin as the conductor insulation (dielectric). ESSEX GROUP, INC. foam conductor insulation is made from polyolefin expanded approximately 33%. Introduced in the U.S. by Essex in 1973, it has been replaced by foam/skin conductor insulations.

Foam Skin Cable -- A jelly filled (polyethylene modified petrolatum) outside plant cable utilizing a foamed polyolefin inner layer covered by air outer layer of solid polyolefin as the conductor insulation (dielectric). ESSEX GROUP, INC. foam/skin insulation is made from polyolefin expanded approximately 50% and covered with a 2 mil skin of solid polyolefin.

Foam-Polyethylene -- A polyethylene compound which has been whipped in the presence of an inert gas. The resulting compound has a lower dielectric constant than does basic polyethylene.

Fraying -- In cabling, a term used to describe the unraveling of a fibrous braid.

Frequency -- The number of times an alternating current reverses itself in one second.

Frequency Power -- Normally the 50 or 60 cycle power available in residential areas.

Frequency Response -- The characteristic of a device denoting the range of frequencies over which it may be used effectively.