Decibel -- An exponential unit to express differences of power level. Example: The decibel is 10 times the common logarithm of the power ratio. It is used to express power gain in amplifiers or power lass in passive circuits or cables.

Delay Line -- A transmission line or equivalent device designed to delay a wave or signal for a specific length of time.

Denier -- A term describing the weight of yarn (not cotton or spun rayon) which in turn determines its physical size.

Derating Factor -- A factor used to reduce a current carrying capacity of a wire when used in other environments from that for which the value was established.

Dielectric -- A non-conducting material or a material having the property that the energy required to establish an electric field is recoverable, in whole or part, as electric energy; or any insulating medium which intervenes between two conductors and permits electrostatic attraction and repulsion to take place across it.

Dielectric Absorption -- The property of an imperfect dielectric whereby there is an accumulation of electric charges within the body of the material when it is placed in an electric field.

Dielectric Breakdown -- Any change in the properties of a dielectric that causes it to become conductive; normally a catastrophic failure of an insulation because of excessive voltage.

Dielectric Constant -- The property of an insulation which determines the electrostatic energy stored per unit volume for unit potential gradient. It is expressed as a ratio. "K" for air is 1.0, while that for polyethylene is 2.2 times that of air. It is also referred to as a Specific Inductive Capacity or Permitivity.

Dielectric Heating -- The heating of an insulating material when placed in a radio frequency field, caused by internal losses during the rapid polarization reversal of molecules in the material.

Dielectric Loss -- The time rate at which electric energy is transformed into heat in a dielectric when it is subjected to a changing electric field.

Dielectric Power Factor -- An expression of energy loss in an electric current due to the effect of the dielectric.

Dielectric Strength -- The maximum voltage insulation can withstand without rupture or breakdown occurring. It is usually expressed as a voltage gradient in volts per unit thickness.

Dielectric Tests -- Tests which consist of the application of voltage higher than the rated voltage for a specific time for the purpose of determining the adequacy against breakdown of insulating materials and spacings under normal conditions.

Digital -- Representation of data by discrete characters.

Dip Coating -- An insulating coating applied to the conductor by passing the conductor through an applicator containing liquid insulating medium. This method can be used for magnet wire.

Direct Current -- Electricity that flows in one direction only.

Direction of Lay -- The lateral direction in which the strands of a cable run over the top of the cable as they receded from an observer looking along the axis of the cable. This is the same designation used for thread direction of screws. ASTM symbols are used to indicate direction with "S" for left hand and "A" for right hand.

Dispersion -- The cause of bandwidth limitations in an optical fiber. Dispersion causes a broadening of input pulses along the length of the fiber. Two major types are (a) mode dispersion caused by differential optical path lengths in a multimode fiber, and (b) material dispersion caused by a differential delay of various wavelengths of light in a wave guide material.

Displacement Current -- A current which exists in addition to ordinary conduction current in AC circuits. It is proportional to the rate of change of the electric field.

Disruptive Discharge -- The sudden and large increase in current through an insulation medium due to the complete failure of the medium under the electrostatic stress.

Dissipation Factor -- The tangent of the loss angle of the insulating material. (Also referred to as loss tangent and approximate power factor.)

Distortion -- An undesired change in wave form as the signal passes through a device.

Distribution Cable -- In a CATV system, the transmission cable from the distribution amplifier to the drop cable.

Disturbed Conductor -- A conductor that receives energy generated by the field of another conductor or an external source such as a transformer.

Disturbing Conductor -- A conductor carrying energy that creates spurious signals in another conductor.

Drain Wire -- An uninsulated stranded or solid conductor which is located directly under a shield. Since it comes in contact with the shield throughout the entire length of the cable, it may be used to terminate the shield and eliminate a considerable amount of dispersion.

Drawing -- The process of pulling metal through a die or a series of dies to achieve a desired diameter.

Drop Cable -- The transmission cable in a CATV system from the distribution cable to a dwelling.

Dual Coaxial Cable -- Two individually insulated conductors laid parallel or twisted and placed within an overall shield and sheath.

Duct -- An overhead or underground tube used for carrying electrical conductors.

Duobond II -- Laminated shielding tape consisting of heat sensitive adhesive, aluminum foil and polyester.

Duofoil -- Belden trademark for a shield in which metallic foil is applied to both sides of a supporting plastic film.

Duplex Cable -- A cable composed of two insulated conductors twisted together with no sheath or outer covering. The assembled cables may or may not have a common covering or sheath.

Durometer -- A measurement used to denote the hardness of a substance (usually of thermosetting and thermoplastic materials).